Prof. Dr. Jochen Feldmann
Academic Research Focus
- Interaction of tailored nanosystems with light
- Dynamics of optically excited charge carriers in hybrid semiconductor nanocrystals
- Solar water splitting and CO2-reduction with hybrid nanocrystals
- Nano- and Bio-plasmonics
- Dynamics of optically excited charge carriers in hybrid semiconductor nanocrystals
- Solar water splitting and CO2-reduction with hybrid nanocrystals
- Nano- and Bio-plasmonics
Fields of Application
Microelectronics, Nanomaterials, Photo-(electro)catalysis, Photonics
Publications
29.
P Bootz, K Frank, J Eichhorn, M Döblinger, T Bagaria, B Nickel, J Feldmann, B Debnath
S-Scheme Interface Between K–C3N4 and FePS3 Fosters Photocatalytic H2 Evolution Journal Article
In: ACS Applied Materials & Interfaces, vol. 16, no. 47, pp. 65610-65619, 2024, ISSN: 1944-8244.
@article{nokey,
title = {S-Scheme Interface Between K\textendashC3N4 and FePS3 Fosters Photocatalytic H2 Evolution},
author = {P Bootz and K Frank and J Eichhorn and M D\"{o}blinger and T Bagaria and B Nickel and J Feldmann and B Debnath},
url = {https://doi.org/10.1021/acsami.4c15236},
doi = {10.1021/acsami.4c15236},
issn = {1944-8244},
year = {2024},
date = {2024-11-27},
journal = {ACS Applied Materials \& Interfaces},
volume = {16},
number = {47},
pages = {65610-65619},
abstract = {In photocatalysis, photogenerated charge separation is pivotal and can be achieved through various mechanisms. Building heterojunctions is a promising method to enhance charge separation, where effective contact and charge exchange between heterojunction components remains challenging. Mostly used synthesis processes for making heterostructures require high temperatures, difficult processes, or expensive materials. Herein, a heterojunction of potassium intercalated graphitic carbon nitride (K-CN) and nanoflakes of iron phosphor trisulfide (FPS) is designed via a simple mechanical grinding process to boost the hydrogen evolution by a factor of more than 25 compared to pure K-CN. This significant improvement is rarely reached by other combinations of two semiconductors without cocatalysts, such as platinum. It can be attributed to the band alignment and band bending of an S-scheme that is validated via optical and X-ray photoelectron spectroscopy. As a consequence, strong quenching of the photoluminescence and significant H2 evolution occur for this unique heterojunction. Furthermore, the excellent durability of the designed photocatalytic heterostructure is confirmed by monitoring the catalysts’ H2-evolution rate and crystal structure after 72 h under light illumination. This study opens up promising and simple pathways for constructing efficient S-scheme heterojunctions for photocatalytic water-splitting.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In photocatalysis, photogenerated charge separation is pivotal and can be achieved through various mechanisms. Building heterojunctions is a promising method to enhance charge separation, where effective contact and charge exchange between heterojunction components remains challenging. Mostly used synthesis processes for making heterostructures require high temperatures, difficult processes, or expensive materials. Herein, a heterojunction of potassium intercalated graphitic carbon nitride (K-CN) and nanoflakes of iron phosphor trisulfide (FPS) is designed via a simple mechanical grinding process to boost the hydrogen evolution by a factor of more than 25 compared to pure K-CN. This significant improvement is rarely reached by other combinations of two semiconductors without cocatalysts, such as platinum. It can be attributed to the band alignment and band bending of an S-scheme that is validated via optical and X-ray photoelectron spectroscopy. As a consequence, strong quenching of the photoluminescence and significant H2 evolution occur for this unique heterojunction. Furthermore, the excellent durability of the designed photocatalytic heterostructure is confirmed by monitoring the catalysts’ H2-evolution rate and crystal structure after 72 h under light illumination. This study opens up promising and simple pathways for constructing efficient S-scheme heterojunctions for photocatalytic water-splitting.
28.
M A Reus, A Krifa, Q A Akkerman, A Biewald, Z Xu, D P Kosbahn, C L Weindl, J Feldmann, A Hartschuh, P Müller-Buschbaum
Layer-By-Layer Printed Metal Hybrid (Cs:FA)PbI3 Perovskite Nanocrystal Solar Cells Journal Article
In: Advanced Optical Materials, vol. n/a, no. n/a, pp. 2301008, 2023, ISSN: 2195-1071.
@article{nokey,
title = {Layer-By-Layer Printed Metal Hybrid (Cs:FA)PbI3 Perovskite Nanocrystal Solar Cells},
author = {M A Reus and A Krifa and Q A Akkerman and A Biewald and Z Xu and D P Kosbahn and C L Weindl and J Feldmann and A Hartschuh and P M\"{u}ller-Buschbaum},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202301008},
doi = {https://doi.org/10.1002/adom.202301008},
issn = {2195-1071},
year = {2023},
date = {2023-09-01},
journal = {Advanced Optical Materials},
volume = {n/a},
number = {n/a},
pages = {2301008},
abstract = {Abstract Mixed halide perovskite nanocrystals in the form of cesium/formamidinium lead triiodide ((Cs:FA)PbI3) offer great potential for efficient and stable solar cells. To date, large-scale production with roll-to-roll compatible deposition methods remains difficult and requires detailed research on each involved processing step. Here, a proof-of-concept study about slot-die coating (printing) the active layer of (Cs:FA)PbI3-based nanocrystal solar cells is presented. Structural and morphological changes during ligand exchange of long-chain oleic acid and oleylamine by Pb(NO3)2, and top-layer FAI passivation are investigated. Ligand exchange improves the processability of the nanocrystal layer and enhances charge transport. It also changes texture from face-on toward edge-on orientation as grazing-incidence X-ray scattering studies indicate. Ligand exchange and FAI passivation redshift photoluminescence and prolong charge carrier lifetime in the printed nanocrystal films. The proof-of-concept feasibility of printing metal halide perovskite nanocrystal films for solar cells is shown by building 20 devices with a median power conversion efficiency of 6.39%.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Mixed halide perovskite nanocrystals in the form of cesium/formamidinium lead triiodide ((Cs:FA)PbI3) offer great potential for efficient and stable solar cells. To date, large-scale production with roll-to-roll compatible deposition methods remains difficult and requires detailed research on each involved processing step. Here, a proof-of-concept study about slot-die coating (printing) the active layer of (Cs:FA)PbI3-based nanocrystal solar cells is presented. Structural and morphological changes during ligand exchange of long-chain oleic acid and oleylamine by Pb(NO3)2, and top-layer FAI passivation are investigated. Ligand exchange improves the processability of the nanocrystal layer and enhances charge transport. It also changes texture from face-on toward edge-on orientation as grazing-incidence X-ray scattering studies indicate. Ligand exchange and FAI passivation redshift photoluminescence and prolong charge carrier lifetime in the printed nanocrystal films. The proof-of-concept feasibility of printing metal halide perovskite nanocrystal films for solar cells is shown by building 20 devices with a median power conversion efficiency of 6.39%.
27.
J Fang, Y Wang, M Kurashvili, S Rieger, W Kasprzyk, Q Wang, J K Stolarczyk, J Feldmann, T Debnath
Simultaneous Hydrogen Generation and Exciplex Stimulated Emission in Photobasic Carbon Dots Journal Article
In: Angewandte Chemie International Edition, vol. 62, no. 33, pp. e202305817, 2023, ISSN: 1433-7851.
@article{nokey,
title = {Simultaneous Hydrogen Generation and Exciplex Stimulated Emission in Photobasic Carbon Dots},
author = {J Fang and Y Wang and M Kurashvili and S Rieger and W Kasprzyk and Q Wang and J K Stolarczyk and J Feldmann and T Debnath},
url = {https://doi.org/10.1002/anie.202305817},
doi = {https://doi.org/10.1002/anie.202305817},
issn = {1433-7851},
year = {2023},
date = {2023-08-14},
urldate = {2023-08-14},
journal = {Angewandte Chemie International Edition},
volume = {62},
number = {33},
pages = {e202305817},
abstract = {Abstract Photocatalytic water splitting is a promising approach to generating sustainable hydrogen. However, the transport of photoelectrons to the catalyst sites, usually within ps-to-ns timescales, is much faster than proton delivery (??s), which limits the activity. Therefore, the acceleration of abstraction of protons from water molecules towards the catalytic sites to keep up with the electron transfer rate can significantly promote hydrogen production. The photobasic effect that is the increase in proton affinity upon excitation offers means to achieve this objective. Herein, we design photobasic carbon dots and identify that internal pyridinic N sites are intrinsically photobasic. This is supported by steady-state and ultrafast spectroscopic measurements that demonstrate proton abstraction within a few picoseconds of excitation. Furthermore, we show that in water, they form a unique four-level lasing scheme with optical gain and stimulated emission. The latter competes with photocatalysis, revealing a rather unique mechanism for efficiency loss, such that the stimulated emission can act as a toggle for photocatalytic activity. This provides additional means of controlling the photocatalytic process and helps the rational design of photocatalytic materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Photocatalytic water splitting is a promising approach to generating sustainable hydrogen. However, the transport of photoelectrons to the catalyst sites, usually within ps-to-ns timescales, is much faster than proton delivery (??s), which limits the activity. Therefore, the acceleration of abstraction of protons from water molecules towards the catalytic sites to keep up with the electron transfer rate can significantly promote hydrogen production. The photobasic effect that is the increase in proton affinity upon excitation offers means to achieve this objective. Herein, we design photobasic carbon dots and identify that internal pyridinic N sites are intrinsically photobasic. This is supported by steady-state and ultrafast spectroscopic measurements that demonstrate proton abstraction within a few picoseconds of excitation. Furthermore, we show that in water, they form a unique four-level lasing scheme with optical gain and stimulated emission. The latter competes with photocatalysis, revealing a rather unique mechanism for efficiency loss, such that the stimulated emission can act as a toggle for photocatalytic activity. This provides additional means of controlling the photocatalytic process and helps the rational design of photocatalytic materials.
26.
Y Zou, J Eichhorn, S Rieger, Y Zheng, S Yuan, L Wolz, L V Spanier, J E Heger, S Yin, C R Everett, L Dai, M Schwartzkopf, C Mu, S V Roth, I D Sharp, C-C Chen, J Feldmann, S D Stranks, P Müller-Buschbaum
Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells Journal Article
In: Nano Energy, vol. 112, pp. 108449, 2023, ISSN: 2211-2855.
@article{nokey,
title = {Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells},
author = {Y Zou and J Eichhorn and S Rieger and Y Zheng and S Yuan and L Wolz and L V Spanier and J E Heger and S Yin and C R Everett and L Dai and M Schwartzkopf and C Mu and S V Roth and I D Sharp and C-C Chen and J Feldmann and S D Stranks and P M\"{u}ller-Buschbaum},
url = {https://www.sciencedirect.com/science/article/pii/S2211285523002860},
doi = {https://doi.org/10.1016/j.nanoen.2023.108449},
issn = {2211-2855},
year = {2023},
date = {2023-04-21},
journal = {Nano Energy},
volume = {112},
pages = {108449},
abstract = {The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr14BF4) maintains 97% of its initial efficiency after 4368 h.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr14BF4) maintains 97% of its initial efficiency after 4368 h.
25.
Y Zou, J Eichhorn, S Rieger, Y Zheng, S Yuan, L Wolz, L V Spanier, J E Heger, S Yin, C R Everett, L Dai, M Schwartzkopf, C Mu, S V Roth, I D Sharp, C-C Chen, J Feldmann, S D Stranks, P Müller-Buschbaum
Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells Journal Article
In: Nano Energy, vol. 112, pp. 108449, 2023, ISSN: 2211-2855.
@article{nokey,
title = {Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells},
author = {Y Zou and J Eichhorn and S Rieger and Y Zheng and S Yuan and L Wolz and L V Spanier and J E Heger and S Yin and C R Everett and L Dai and M Schwartzkopf and C Mu and S V Roth and I D Sharp and C-C Chen and J Feldmann and S D Stranks and P M\"{u}ller-Buschbaum},
url = {https://www.sciencedirect.com/science/article/pii/S2211285523002860},
doi = {https://doi.org/10.1016/j.nanoen.2023.108449},
issn = {2211-2855},
year = {2023},
date = {2023-04-14},
journal = {Nano Energy},
volume = {112},
pages = {108449},
abstract = {The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr14BF4) maintains 97% of its initial efficiency after 4368 h.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr14BF4) maintains 97% of its initial efficiency after 4368 h.
24.
A Dey, S Strohmair, F He, Q A Akkerman, J Feldmann
Fast electron and slow hole spin relaxation in CsPbI3 nanocrystals Journal Article
In: Applied Physics Letters, vol. 121, no. 20, pp. 201106, 2022, ISSN: 0003-6951.
@article{nokey,
title = {Fast electron and slow hole spin relaxation in CsPbI3 nanocrystals},
author = {A Dey and S Strohmair and F He and Q A Akkerman and J Feldmann},
url = {https://doi.org/10.1063/5.0103102},
doi = {10.1063/5.0103102},
issn = {0003-6951},
year = {2022},
date = {2022-11-14},
journal = {Applied Physics Letters},
volume = {121},
number = {20},
pages = {201106},
abstract = {Spin-dependent properties of lead halide perovskites (LHPs) have recently gained significant attention paving their way toward spin-optoelectronic applications. However, separate measurements of the electron and hole spin relaxation rates are so far missing in LHPs. The knowledge of the electron and hole spin relaxation timescales is necessary to understand the spin-dependent properties of LHPs. Here, we report on the spin polarization dynamics in CsPbI3 nanocrystals (NCs). We employ polarization dependent ultrafast differential transmission spectroscopy (DTS) at room temperature to study the spin polarization dynamics in this system. In the case of pure CsPbI3 NCs, it is not possible to measure separately electron and hole spin relaxation rates from the polarization dependent DTS. Here, we introduce the soluble fullerene derivative PC60BM as an electron acceptor along with CsPbI3 to create an imbalance between the photoexcited electrons and holes in the NCs and, thus, affecting their spin-dependent carrier distribution. CsPbI3:PC60BM blend sample shows a distinct difference in the spin dependent kinetics of the DTS spectra as compared to the NCs-only sample. With the help of a kinetic model for the spin-dependent charge carrier distributions, we separately determine the electron and hole spin relaxation times in CsPbI3 NCs. We find that the room temperature hole spin lifetime (τh ∼ 5 ps) is ∼13 times longer than the electron spin lifetime (τe ∼ 0.4 ps). We ascribe the fast electron spin relaxation to the presence of strong spin\textendashorbit coupling in the conduction band, which is ineffective for holes in the s-type valence band.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Spin-dependent properties of lead halide perovskites (LHPs) have recently gained significant attention paving their way toward spin-optoelectronic applications. However, separate measurements of the electron and hole spin relaxation rates are so far missing in LHPs. The knowledge of the electron and hole spin relaxation timescales is necessary to understand the spin-dependent properties of LHPs. Here, we report on the spin polarization dynamics in CsPbI3 nanocrystals (NCs). We employ polarization dependent ultrafast differential transmission spectroscopy (DTS) at room temperature to study the spin polarization dynamics in this system. In the case of pure CsPbI3 NCs, it is not possible to measure separately electron and hole spin relaxation rates from the polarization dependent DTS. Here, we introduce the soluble fullerene derivative PC60BM as an electron acceptor along with CsPbI3 to create an imbalance between the photoexcited electrons and holes in the NCs and, thus, affecting their spin-dependent carrier distribution. CsPbI3:PC60BM blend sample shows a distinct difference in the spin dependent kinetics of the DTS spectra as compared to the NCs-only sample. With the help of a kinetic model for the spin-dependent charge carrier distributions, we separately determine the electron and hole spin relaxation times in CsPbI3 NCs. We find that the room temperature hole spin lifetime (τh ∼ 5 ps) is ∼13 times longer than the electron spin lifetime (τe ∼ 0.4 ps). We ascribe the fast electron spin relaxation to the presence of strong spin–orbit coupling in the conduction band, which is ineffective for holes in the s-type valence band.
23.
I Vinçon, F J Wendisch, D De Gregorio, S D Pritzl, Q A Akkerman, H Ren, L De S. Menezes, S A Maier, J Feldmann
Strong Polarization Dependent Nonlinear Excitation of a Perovskite Nanocrystal Monolayer on a Chiral Dielectric Nanoantenna Array Journal Article
In: ACS Photonics, vol. 9, iss. 11, pp. 3506-3514, 2022.
@article{nokey,
title = {Strong Polarization Dependent Nonlinear Excitation of a Perovskite Nanocrystal Monolayer on a Chiral Dielectric Nanoantenna Array},
author = {I Vin\c{c}on and F J Wendisch and D De Gregorio and S D Pritzl and Q A Akkerman and H Ren and L De S. Menezes and S A Maier and J Feldmann},
url = {https://doi.org/10.1021/acsphotonics.2c00159},
doi = {10.1021/acsphotonics.2c00159},
year = {2022},
date = {2022-08-17},
urldate = {2022-08-17},
journal = {ACS Photonics},
volume = {9},
issue = {11},
pages = {3506-3514},
abstract = {With their unique optoelectronic properties, perovskite nanocrystals are highly advantageous semiconductor materials for tailored light applications including an interaction with circularly polarized light. Although chiral perovskite nanocrystals have been obtained by the adsorption of chiral molecules, their chiroptical response is still intrinsically weak. Alternatively, perovskites have been combined with artificial chiral surfaces demonstrating enhanced chiroptical responses. However, bulk perovskite films of considerable thickness were required, mitigating the perovskite’s photoluminescence efficiency and processability. Here we developed a hybrid system of a dielectric chiral nanoantenna array that was coated with a monolayer of cubic all-inorganic lead halide perovskite nanocrystals. By tuning the thickness of the perovskite film down to one monolayer of nanocrystals, we restricted the interactions exclusively to the near-field regime. The chiral surface built of z-shaped Si nanoantennas features pronounced chiral resonances in the visible to IR region. We demonstrate that the two-photon excited photoluminescence emission of the nanocrystals can be enhanced by up to one order of magnitude in this configuration. This emission increase is controllable by the choice of the excitation wavelength and polarization with an asymmetry in emission of up to 25% upon left and right circularly polarized illumination. Altogether, our findings demonstrate a pathway to an all-optical control and modulation of perovskite light emission via strong polarization sensitive light\textendashmatter interactions in the near-field, rendering this hybrid system interesting for sensing and display technologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
With their unique optoelectronic properties, perovskite nanocrystals are highly advantageous semiconductor materials for tailored light applications including an interaction with circularly polarized light. Although chiral perovskite nanocrystals have been obtained by the adsorption of chiral molecules, their chiroptical response is still intrinsically weak. Alternatively, perovskites have been combined with artificial chiral surfaces demonstrating enhanced chiroptical responses. However, bulk perovskite films of considerable thickness were required, mitigating the perovskite’s photoluminescence efficiency and processability. Here we developed a hybrid system of a dielectric chiral nanoantenna array that was coated with a monolayer of cubic all-inorganic lead halide perovskite nanocrystals. By tuning the thickness of the perovskite film down to one monolayer of nanocrystals, we restricted the interactions exclusively to the near-field regime. The chiral surface built of z-shaped Si nanoantennas features pronounced chiral resonances in the visible to IR region. We demonstrate that the two-photon excited photoluminescence emission of the nanocrystals can be enhanced by up to one order of magnitude in this configuration. This emission increase is controllable by the choice of the excitation wavelength and polarization with an asymmetry in emission of up to 25% upon left and right circularly polarized illumination. Altogether, our findings demonstrate a pathway to an all-optical control and modulation of perovskite light emission via strong polarization sensitive light–matter interactions in the near-field, rendering this hybrid system interesting for sensing and display technologies.
22.
M Kurashvili, I Polishchuk, A Lang, S Strohmair, A F Richter, S Rieger, T Debnath, B Pokroy, J Feldmann
Disorder and Confinement Effects to Tune the Optical Properties of Amino Acid Doped Cu2O Crystals Journal Article
In: Advanced Functional Materials, vol. 32, no. 27, pp. 2202121, 2022, ISSN: 1616-301X.
@article{nokey,
title = {Disorder and Confinement Effects to Tune the Optical Properties of Amino Acid Doped Cu2O Crystals},
author = {M Kurashvili and I Polishchuk and A Lang and S Strohmair and A F Richter and S Rieger and T Debnath and B Pokroy and J Feldmann},
url = {https://doi.org/10.1002/adfm.202202121},
doi = {https://doi.org/10.1002/adfm.202202121},
issn = {1616-301X},
year = {2022},
date = {2022-07-01},
urldate = {2022-07-01},
journal = {Advanced Functional Materials},
volume = {32},
number = {27},
pages = {2202121},
abstract = {Abstract Biominerals are organic?inorganic nanocomposites exhibiting remarkable properties due to their unique configuration. Using optical spectroscopy and theoretical modeling, it is shown that the optical properties of a model bioinspired system, an inorganic semiconductor host (Cu2O) grown in the presence of amino acids (AAs), are strongly influenced by the latter. The absorption and photoluminescence excitation spectra of Cu2O-AAs blue-shift with growing AA content, indicating band gap widening. This is attributed to the void-induced quantum confinement effects. Surprisingly, no such shift occurs in the emission spectra. The theoretical model, assuming an inhomogeneous AA distribution within Cu2O-AAs due to compositional disorder, explains the deviating behavior of the photoluminescence. The model predicts that the potential causing the confinement effects becomes a function of the local AA density. It results in a Gaussian band gap distribution that shapes the optical properties of Cu2O-AAs. Imitating and harnessing the process of biomineralization can pave the way toward new functional materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Biominerals are organic?inorganic nanocomposites exhibiting remarkable properties due to their unique configuration. Using optical spectroscopy and theoretical modeling, it is shown that the optical properties of a model bioinspired system, an inorganic semiconductor host (Cu2O) grown in the presence of amino acids (AAs), are strongly influenced by the latter. The absorption and photoluminescence excitation spectra of Cu2O-AAs blue-shift with growing AA content, indicating band gap widening. This is attributed to the void-induced quantum confinement effects. Surprisingly, no such shift occurs in the emission spectra. The theoretical model, assuming an inhomogeneous AA distribution within Cu2O-AAs due to compositional disorder, explains the deviating behavior of the photoluminescence. The model predicts that the potential causing the confinement effects becomes a function of the local AA density. It results in a Gaussian band gap distribution that shapes the optical properties of Cu2O-AAs. Imitating and harnessing the process of biomineralization can pave the way toward new functional materials.
21.
L Wu, Y Wang, M Kurashvili, A Dey, M Cao, M Döblinger, Q Zhang, J Feldmann, H Huang, T Debnath
Interfacial Manganese-Doping in CsPbBr3 Nanoplatelets by Employing a Molecular Shuttle Journal Article
In: Angewandte Chemie International Edition, vol. 61, no. 15, pp. e202115852, 2022, ISSN: 1433-7851.
@article{nokey,
title = {Interfacial Manganese-Doping in CsPbBr3 Nanoplatelets by Employing a Molecular Shuttle},
author = {L Wu and Y Wang and M Kurashvili and A Dey and M Cao and M D\"{o}blinger and Q Zhang and J Feldmann and H Huang and T Debnath},
url = {https://doi.org/10.1002/anie.202115852},
doi = {https://doi.org/10.1002/anie.202115852},
issn = {1433-7851},
year = {2022},
date = {2022-04-04},
urldate = {2022-04-04},
journal = {Angewandte Chemie International Edition},
volume = {61},
number = {15},
pages = {e202115852},
abstract = {Abstract Mn-doping in cesium lead halide perovskite nanoplatelets (NPls) is of particular importance where strong quantum confinement plays a significant role towards the exciton?dopant coupling. In this work, we report an immiscible bi-phasic strategy for post-synthetic Mn-doping of CsPbX3 (X=Br, Cl) NPls. A systematic study shows that electron-donating oleylamine acts as a shuttle ligand to transport MnX2 through the water?hexane interface and deliver it to the NPls. The halide anion also plays an essential role in maintaining an appropriate radius of Mn2+ and thus fulfilling the octahedral factor required for the formation of perovskite crystals. By varying the thickness of parent NPls, we can tune the dopant incorporation and, consequently, the exciton-to-dopant energy transfer process in doped NPls. Time-resolved optical measurements offer a detailed insight into the exciton-to-dopant energy transfer process. This new approach for post-synthetic cation doping paves a way towards exploring the cation exchange process in several other halide perovskites at the polar?nonpolar interface.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Mn-doping in cesium lead halide perovskite nanoplatelets (NPls) is of particular importance where strong quantum confinement plays a significant role towards the exciton?dopant coupling. In this work, we report an immiscible bi-phasic strategy for post-synthetic Mn-doping of CsPbX3 (X=Br, Cl) NPls. A systematic study shows that electron-donating oleylamine acts as a shuttle ligand to transport MnX2 through the water?hexane interface and deliver it to the NPls. The halide anion also plays an essential role in maintaining an appropriate radius of Mn2+ and thus fulfilling the octahedral factor required for the formation of perovskite crystals. By varying the thickness of parent NPls, we can tune the dopant incorporation and, consequently, the exciton-to-dopant energy transfer process in doped NPls. Time-resolved optical measurements offer a detailed insight into the exciton-to-dopant energy transfer process. This new approach for post-synthetic cation doping paves a way towards exploring the cation exchange process in several other halide perovskites at the polar?nonpolar interface.
20.
Y Wang, E-P Yao, L Wu, J Feldmann, J K Stolarczyk
A Multi-Layer Device for Light-Triggered Hydrogen Production from Alkaline Methanol Journal Article
In: Angewandte Chemie International Edition, vol. 60, no. 51, pp. 26694-26701, 2021, ISSN: 1433-7851.
@article{nokey,
title = {A Multi-Layer Device for Light-Triggered Hydrogen Production from Alkaline Methanol},
author = {Y Wang and E-P Yao and L Wu and J Feldmann and J K Stolarczyk},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202109979},
doi = {https://doi.org/10.1002/anie.202109979},
issn = {1433-7851},
year = {2021},
date = {2021-10-13},
journal = {Angewandte Chemie International Edition},
volume = {60},
number = {51},
pages = {26694-26701},
abstract = {Abstract It usually requires high temperature and high pressure to reform methanol with water to hydrogen with high turnover frequency (TOF). Here we show that hydrogen can be produced from alkaline methanol on a light-triggered multi-layer system with a very high hydrogen evolution rate up to ca. 1 μmol s−1 under the illumination of a standard Pt-decorated carbon nitride. The system can achieve a remarkable TOF up to 1.8×106 moles of hydrogen per mole of Pt per hour under mild conditions. The total turnover number (TTN) of 470 000 measured over 38 hours is among the highest reported. The system does not lead to any COx emissions, hence it could feed clean hydrogen to fuel cells. In contrast to a slurry system, the proposed multi-layer system avoids particle aggregation and effectively uses light and Pt active sites. The performance is also attributed to the light-triggered reforming of alkaline methanol. This notable performance is a promising step toward practical light-driven hydrogen generation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract It usually requires high temperature and high pressure to reform methanol with water to hydrogen with high turnover frequency (TOF). Here we show that hydrogen can be produced from alkaline methanol on a light-triggered multi-layer system with a very high hydrogen evolution rate up to ca. 1 μmol s−1 under the illumination of a standard Pt-decorated carbon nitride. The system can achieve a remarkable TOF up to 1.8×106 moles of hydrogen per mole of Pt per hour under mild conditions. The total turnover number (TTN) of 470 000 measured over 38 hours is among the highest reported. The system does not lead to any COx emissions, hence it could feed clean hydrogen to fuel cells. In contrast to a slurry system, the proposed multi-layer system avoids particle aggregation and effectively uses light and Pt active sites. The performance is also attributed to the light-triggered reforming of alkaline methanol. This notable performance is a promising step toward practical light-driven hydrogen generation.
19.
S Rieger, T Fürmann, J K Stolarczyk, J Feldmann
Optically Induced Coherent Phonons in Bismuth Oxyiodide (BiOI) Nanoplatelets Journal Article
In: Nano Letters, 2021, ISSN: 1530-6984.
@article{,
title = {Optically Induced Coherent Phonons in Bismuth Oxyiodide (BiOI) Nanoplatelets},
author = {S Rieger and T F\"{u}rmann and J K Stolarczyk and J Feldmann},
url = {https://doi.org/10.1021/acs.nanolett.1c00530},
doi = {10.1021/acs.nanolett.1c00530},
issn = {1530-6984},
year = {2021},
date = {2021-06-30},
journal = {Nano Letters},
abstract = {Bismuth oxyiodide (BiOI) is a promising material for photocatalysis combining intriguing optical and structural properties. We show that excitation by a femtosecond laser pulse creates coherent phonons inducing a time-variant oscillating modulation of the optical density. We find that the two underlying frequencies originate from lattice vibrations along the [001] crystallographic axis, the stacking direction of oppositely charged layers in BiOI. This is consistent with a subpicosecond charge separation driven by a built-in dipolar field. This partially screens the field, launching coherent phonons. Further, we determine the two major dephasing mechanisms that lead to the loss of vibronic coherence: (i) the anharmonic decay of an optical phonon into two acoustic phonons and (ii) phonon-carrier scattering. Our results provide a direct demonstration of the presence of an electric field in BiOI along the [001] axis and show its role in efficient charge separation that is crucial for photocatalytic applications of BiOI.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Bismuth oxyiodide (BiOI) is a promising material for photocatalysis combining intriguing optical and structural properties. We show that excitation by a femtosecond laser pulse creates coherent phonons inducing a time-variant oscillating modulation of the optical density. We find that the two underlying frequencies originate from lattice vibrations along the [001] crystallographic axis, the stacking direction of oppositely charged layers in BiOI. This is consistent with a subpicosecond charge separation driven by a built-in dipolar field. This partially screens the field, launching coherent phonons. Further, we determine the two major dephasing mechanisms that lead to the loss of vibronic coherence: (i) the anharmonic decay of an optical phonon into two acoustic phonons and (ii) phonon-carrier scattering. Our results provide a direct demonstration of the presence of an electric field in BiOI along the [001] axis and show its role in efficient charge separation that is crucial for photocatalytic applications of BiOI.
18.
A Dey, J Ye, A De, E Debroye, S K Ha, E Bladt, A S Kshirsagar, Z Wang, J Yin, Y Wang, L N Quan, F Yan, M Gao, X Li, J Shamsi, T Debnath, M Cao, M A Scheel, S Kumar, J A Steele, M Gerhard, L Chouhan, K Xu, X-G Wu, Y Li, Y Zhang, A Dutta, C Han, I Vincon, A L Rogach, A Nag, A Samanta, B A Korgel, C-J Shih, D R Gamelin, D H Son, H Zeng, H Zhong, H Sun, H V Demir, I G Scheblykin, I Mora-Seró, J K Stolarczyk, J Z Zhang, J Feldmann, J Hofkens, J M Luther, J Pérez-Prieto, L Li, L Manna, M I Bodnarchuk, M V Kovalenko, M B J Roeffaers, N Pradhan, O F Mohammed, O M Bakr, P Yang, P Müller-Buschbaum, P V Kamat, Q Bao, Q Zhang, R Krahne, R E Galian, S D Stranks, S Bals, V Biju, W A Tisdale, Y Yan, R L Z Hoye, L Polavarapu
State of the Art and Prospects for Halide Perovskite Nanocrystals Journal Article
In: ACS Nano, 2021, ISSN: 1936-0851.
@article{,
title = {State of the Art and Prospects for Halide Perovskite Nanocrystals},
author = {A Dey and J Ye and A De and E Debroye and S K Ha and E Bladt and A S Kshirsagar and Z Wang and J Yin and Y Wang and L N Quan and F Yan and M Gao and X Li and J Shamsi and T Debnath and M Cao and M A Scheel and S Kumar and J A Steele and M Gerhard and L Chouhan and K Xu and X-G Wu and Y Li and Y Zhang and A Dutta and C Han and I Vincon and A L Rogach and A Nag and A Samanta and B A Korgel and C-J Shih and D R Gamelin and D H Son and H Zeng and H Zhong and H Sun and H V Demir and I G Scheblykin and I Mora-Ser\'{o} and J K Stolarczyk and J Z Zhang and J Feldmann and J Hofkens and J M Luther and J P\'{e}rez-Prieto and L Li and L Manna and M I Bodnarchuk and M V Kovalenko and M B J Roeffaers and N Pradhan and O F Mohammed and O M Bakr and P Yang and P M\"{u}ller-Buschbaum and P V Kamat and Q Bao and Q Zhang and R Krahne and R E Galian and S D Stranks and S Bals and V Biju and W A Tisdale and Y Yan and R L Z Hoye and L Polavarapu},
url = {https://doi.org/10.1021/acsnano.0c08903},
doi = {10.1021/acsnano.0c08903},
issn = {1936-0851},
year = {2021},
date = {2021-06-17},
urldate = {2021-06-17},
journal = {ACS Nano},
abstract = {Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
17.
T Debnath, D Sarker, H Huang, Z-K Han, A Dey, L Polavarapu, S V Levchenko, J Feldmann
Coherent vibrational dynamics reveals lattice anharmonicity in organic–inorganic halide perovskite nanocrystals Journal Article
In: Nature Communications, vol. 12, no. 1, pp. 2629, 2021, ISSN: 2041-1723.
@article{,
title = {Coherent vibrational dynamics reveals lattice anharmonicity in organic\textendashinorganic halide perovskite nanocrystals},
author = {T Debnath and D Sarker and H Huang and Z-K Han and A Dey and L Polavarapu and S V Levchenko and J Feldmann},
url = {https://doi.org/10.1038/s41467-021-22934-2},
doi = {10.1038/s41467-021-22934-2},
issn = {2041-1723},
year = {2021},
date = {2021-05-11},
journal = {Nature Communications},
volume = {12},
number = {1},
pages = {2629},
abstract = {The halide ions of organic-inorganic hybrid perovskites can strongly influence the interaction between the central organic moiety and the inorganic metal halide octahedral units and thus their lattice vibrations. Here, we report the halide-ion-dependent vibrational coherences in formamidinium lead halide (FAPbX3, X = Br, I) perovskite nanocrystals (PNCs) via the combination of femtosecond pump\textendashprobe spectroscopy and density functional theory calculations. We find that the FAPbX3 PNCs generate halide-dependent coherent vibronic wave packets upon above-bandgap non-resonant excitation. More importantly, we observe several higher harmonics of the fundamental modes for FAPbI3 PNCs as compared to FAPbBr3 PNCs. This is likely due to the weaker interaction between the central FA moiety and the inorganic cage for FAPbI3 PNCs, and thus the PbI64− unit can vibrate more freely. This weakening reveals the intrinsic anharmonicity in the Pb-I framework, and thus facilitating the energy transfer into overtone and combination bands. These findings not only unveil the superior stability of Br\textendashbased PNCs over I\textendashbased PNCs but are also important for a better understanding of their electronic and polaronic properties.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The halide ions of organic-inorganic hybrid perovskites can strongly influence the interaction between the central organic moiety and the inorganic metal halide octahedral units and thus their lattice vibrations. Here, we report the halide-ion-dependent vibrational coherences in formamidinium lead halide (FAPbX3, X = Br, I) perovskite nanocrystals (PNCs) via the combination of femtosecond pump–probe spectroscopy and density functional theory calculations. We find that the FAPbX3 PNCs generate halide-dependent coherent vibronic wave packets upon above-bandgap non-resonant excitation. More importantly, we observe several higher harmonics of the fundamental modes for FAPbI3 PNCs as compared to FAPbBr3 PNCs. This is likely due to the weaker interaction between the central FA moiety and the inorganic cage for FAPbI3 PNCs, and thus the PbI64− unit can vibrate more freely. This weakening reveals the intrinsic anharmonicity in the Pb-I framework, and thus facilitating the energy transfer into overtone and combination bands. These findings not only unveil the superior stability of Br–based PNCs over I–based PNCs but are also important for a better understanding of their electronic and polaronic properties.
16.
J Fang, T Debnath, S Bhattacharyya, M Döblinger, J Feldmann, J K Stolarczyk
Photobase effect for just-in-time delivery in photocatalytic hydrogen generation Journal Article
In: Nature Communications, vol. 11, no. 1, pp. 5179, 2020, ISSN: 2041-1723.
@article{nokey,
title = {Photobase effect for just-in-time delivery in photocatalytic hydrogen generation},
author = {J Fang and T Debnath and S Bhattacharyya and M D\"{o}blinger and J Feldmann and J K Stolarczyk},
url = {https://doi.org/10.1038/s41467-020-18583-6},
doi = {10.1038/s41467-020-18583-6},
issn = {2041-1723},
year = {2020},
date = {2020-10-14},
journal = {Nature Communications},
volume = {11},
number = {1},
pages = {5179},
abstract = {Carbon dots (CDs) are a promising nanomaterial for photocatalytic applications. However, the mechanism of the photocatalytic processes remains the subject of a debate due to the complex internal structure of the CDs, comprising crystalline and molecular units embedded in an amorphous matrix, rendering the analysis of the charge and energy transfer pathways between the constituent parts very challenging. Here we propose that the photobasic effect, that is the abstraction of a proton from water upon excitation by light, facilitates the photoexcited electron transfer to the proton. We show that the controlled inclusion in CDs of a model photobase, acridine, resembling the molecular moieties found in photocatalytically active CDs, strongly increases hydrogen generation. Ultrafast spectroscopy measurements reveal proton transfer within 30 ps of the excitation. This way, we use a model system to show that the photobasic effect may be contributing to the photocatalytic H2 generation of carbon nanomaterials and suggest that it may be tuned to achieve further improvements. The study demonstrates the critical role of the understanding the dynamics of the CDs in the design of next generation photocatalysts.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbon dots (CDs) are a promising nanomaterial for photocatalytic applications. However, the mechanism of the photocatalytic processes remains the subject of a debate due to the complex internal structure of the CDs, comprising crystalline and molecular units embedded in an amorphous matrix, rendering the analysis of the charge and energy transfer pathways between the constituent parts very challenging. Here we propose that the photobasic effect, that is the abstraction of a proton from water upon excitation by light, facilitates the photoexcited electron transfer to the proton. We show that the controlled inclusion in CDs of a model photobase, acridine, resembling the molecular moieties found in photocatalytically active CDs, strongly increases hydrogen generation. Ultrafast spectroscopy measurements reveal proton transfer within 30 ps of the excitation. This way, we use a model system to show that the photobasic effect may be contributing to the photocatalytic H2 generation of carbon nanomaterials and suggest that it may be tuned to achieve further improvements. The study demonstrates the critical role of the understanding the dynamics of the CDs in the design of next generation photocatalysts.
15.
S Strohmair, A Dey, Y Tong, L Polavarapu, B J Bohn, J Feldmann
Spin Polarization Dynamics of Free Charge Carriers in CsPbI3 Nanocrystals Journal Article
In: Nano Letters, vol. 20, no. 7, pp. 4724-4730, 2020, ISSN: 1530-6984.
@article{,
title = {Spin Polarization Dynamics of Free Charge Carriers in CsPbI3 Nanocrystals},
author = {S Strohmair and A Dey and Y Tong and L Polavarapu and B J Bohn and J Feldmann},
url = {\<Go to ISI\>://WOS:000548893200004},
doi = {10.1021/acs.nanolett.9b05325},
issn = {1530-6984},
year = {2020},
date = {2020-07-08},
journal = {Nano Letters},
volume = {20},
number = {7},
pages = {4724-4730},
abstract = {Lead halide perovskites (LHPs) exhibit large spin-orbit coupling (SOC), leading to only twofold-degenerate valence and conduction bands and therefore allowing for efficient optical orientation. This makes them ideal materials to study charge carrier spins. With this study we elucidate the spin dynamics of photoexcited charge carriers and the underlying spin relaxation mechanisms in CsPbI3 nanocrystals by employing time-resolved differential transmission spectroscopy (DTS). We find that the photoinduced spin polarization significantly diminishes during thermalization and cooling toward the energetically favorable band edge. Temperature-dependent DTS reveals a decay in spin polarization that is more than 1 order of magnitude faster at room temperature (3 ps) than at cryogenic temperatures (32 ps). We propose that spin relaxation of free charge carriers in large-SOC materials like LHPs occurs as a result of carrier-phonon scattering, as described by the Elliott-Yafet mechanism.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lead halide perovskites (LHPs) exhibit large spin-orbit coupling (SOC), leading to only twofold-degenerate valence and conduction bands and therefore allowing for efficient optical orientation. This makes them ideal materials to study charge carrier spins. With this study we elucidate the spin dynamics of photoexcited charge carriers and the underlying spin relaxation mechanisms in CsPbI3 nanocrystals by employing time-resolved differential transmission spectroscopy (DTS). We find that the photoinduced spin polarization significantly diminishes during thermalization and cooling toward the energetically favorable band edge. Temperature-dependent DTS reveals a decay in spin polarization that is more than 1 order of magnitude faster at room temperature (3 ps) than at cryogenic temperatures (32 ps). We propose that spin relaxation of free charge carriers in large-SOC materials like LHPs occurs as a result of carrier-phonon scattering, as described by the Elliott-Yafet mechanism.
14.
M Gramlich, B J Bohn, Y Tong, L Polavarapu, J Feldmann, A S Urban
Thickness-Dependence of Exciton-Exciton Annihilation in Halide Perovskite Nanoplatelets Journal Article
In: Journal of Physical Chemistry Letters, vol. 11, no. 13, pp. 5361-5366, 2020, ISSN: 1948-7185.
@article{,
title = {Thickness-Dependence of Exciton-Exciton Annihilation in Halide Perovskite Nanoplatelets},
author = {M Gramlich and B J Bohn and Y Tong and L Polavarapu and J Feldmann and A S Urban},
url = {\<Go to ISI\>://WOS:000547468400064},
doi = {10.1021/acs.jpclett.0c01291},
issn = {1948-7185},
year = {2020},
date = {2020-06-14},
journal = {Journal of Physical Chemistry Letters},
volume = {11},
number = {13},
pages = {5361-5366},
abstract = {Exciton-exciton annihilation (EEA) and Auger recombination are detrimental processes occurring in semiconductor optoelectronic devices at high carrier densities. Despite constituting one of the main obstacles for realizing lasing in semiconductor nanocrystals (NCs), the dependencies on NC size are not fully understood, especially for those with both weakly and strongly confined dimensions. Here, we use differential transmission spectroscopy to investigate the dependence of EEA on the physical dimensions of thickness-controlled 2D halide perovskite nanoplatelets (NPIs). We find the EEA lifetimes to be extremely short on the order of 7-60 ps. Moreover, they are strongly determined by the NP1 thickness with a power law dependence according to tau(2) proportional to d(5.3). Additional measurements show that the EEA lifetimes also increase for NPIs with larger lateral dimensions. dimensions is critical for deciphering the fundamental laws governing These results show that a precise control of the physical the process especially in 1D and 2D NCs.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Exciton-exciton annihilation (EEA) and Auger recombination are detrimental processes occurring in semiconductor optoelectronic devices at high carrier densities. Despite constituting one of the main obstacles for realizing lasing in semiconductor nanocrystals (NCs), the dependencies on NC size are not fully understood, especially for those with both weakly and strongly confined dimensions. Here, we use differential transmission spectroscopy to investigate the dependence of EEA on the physical dimensions of thickness-controlled 2D halide perovskite nanoplatelets (NPIs). We find the EEA lifetimes to be extremely short on the order of 7-60 ps. Moreover, they are strongly determined by the NP1 thickness with a power law dependence according to tau(2) proportional to d(5.3). Additional measurements show that the EEA lifetimes also increase for NPIs with larger lateral dimensions. dimensions is critical for deciphering the fundamental laws governing These results show that a precise control of the physical the process especially in 1D and 2D NCs.
13.
A Dey, A F Richter, T Debnath, H Huang, L Polavarapu, J Feldmann
Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals Journal Article
In: Acs Nano, vol. 14, no. 5, pp. 5855-5861, 2020, ISSN: 1936-0851.
@article{,
title = {Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals},
author = {A Dey and A F Richter and T Debnath and H Huang and L Polavarapu and J Feldmann},
url = {\<Go to ISI\>://WOS:000537682300069},
doi = {10.1021/acsnano.0c00997},
issn = {1936-0851},
year = {2020},
date = {2020-05-26},
journal = {Acs Nano},
volume = {14},
number = {5},
pages = {5855-5861},
abstract = {Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites.
12.
S Paul, E Bladt, A F Richter, M Doblinger, Y Tong, H Huang, A Dey, S Bals, T Debnath, L Polavarapu, J Feldmann
Manganese-Doping-Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden-Popper Defects Journal Article
In: Angewandte Chemie-International Edition, vol. 59, no. 17, pp. 6794-6799, 2020, ISSN: 1433-7851.
@article{,
title = {Manganese-Doping-Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden-Popper Defects},
author = {S Paul and E Bladt and A F Richter and M Doblinger and Y Tong and H Huang and A Dey and S Bals and T Debnath and L Polavarapu and J Feldmann},
url = {\<Go to ISI\>://WOS:000525279800024},
doi = {10.1002/anie.201914473},
issn = {1433-7851},
year = {2020},
date = {2020-04-20},
journal = {Angewandte Chemie-International Edition},
volume = {59},
number = {17},
pages = {6794-6799},
abstract = {The concept of doping Mn2+ ions into II-VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+-related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of RuddlesdenPopper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single-crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The concept of doping Mn2+ ions into II-VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+-related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of RuddlesdenPopper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single-crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.
11.
A Dey, A F Richter, T Debnath, H Huang, L Polavarapu, J Feldmann
Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals Journal Article
In: ACS Nano, vol. 14, no. 5, pp. 5855-5861, 2020, ISSN: 1936-0851.
@article{nokey,
title = {Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals},
author = {A Dey and A F Richter and T Debnath and H Huang and L Polavarapu and J Feldmann},
url = {https://doi.org/10.1021/acsnano.0c00997},
doi = {10.1021/acsnano.0c00997},
issn = {1936-0851},
year = {2020},
date = {2020-04-16},
journal = {ACS Nano},
volume = {14},
number = {5},
pages = {5855-5861},
abstract = {Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites.
10.
B Charles, M T Weller, S Rieger, L E Hatcher, P F Henry, J Feldmann, D Wolverson, C C Wilson
Phase Behavior and Substitution Limit of Mixed Cesium-Formamidinium Lead Triiodide Perovskites Journal Article
In: Chemistry of Materials, vol. 32, no. 6, pp. 2282-2291, 2020, ISSN: 0897-4756.
@article{,
title = {Phase Behavior and Substitution Limit of Mixed Cesium-Formamidinium Lead Triiodide Perovskites},
author = {B Charles and M T Weller and S Rieger and L E Hatcher and P F Henry and J Feldmann and D Wolverson and C C Wilson},
url = {\<Go to ISI\>://WOS:000526391300009},
doi = {10.1021/acs.chemmater.9b04032},
issn = {0897-4756},
year = {2020},
date = {2020-03-24},
journal = {Chemistry of Materials},
volume = {32},
number = {6},
pages = {2282-2291},
abstract = {The mixed cation lead iodide perovskite photovoltaics show improved stability following site substitution of cesium ions (Cs+) onto the formamidinium cation sites (FA(+)) of (CH(NH2)(2)PbI3 (FAPbI(3)) and increased resistance to formation of the undesirable.-phase. The structural phase behavior of Cs(0.1)FA(0.9)PbI(3) has been investigated by neutron powder diffraction (NPD), complemented by single crystal and power X-ray diffraction and photoluminescence spectroscopy. The Cs-substitution limit has been determined to be less than 15%, and the cubic alpha-phase, Cs(0.1)FA(0.9)PbI(3), is shown to be synthesizable in bulk and stable at 300 K. On cooling the cubic Cs(0.1)FA(0.9)PbI(3), a slow, second-order cubic to tetragonal transition is observed close to 290 K, with variable temperature NPD indicating the presence of the tetragonal beta-phase, adopting the space group P4/mbm between 290 and 180 K. An orthorhombic phase or twinned tetragonal phase is formed below 180 K, and the temperature for further transition to a disordered state is lowered to 125 K compared to that seen in phase pure alpha-FAPbI(3) (140 K). These results demonstrate the importance of understanding the effect of cation site substitution on structure-property relationships in perovskite materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The mixed cation lead iodide perovskite photovoltaics show improved stability following site substitution of cesium ions (Cs+) onto the formamidinium cation sites (FA(+)) of (CH(NH2)(2)PbI3 (FAPbI(3)) and increased resistance to formation of the undesirable.-phase. The structural phase behavior of Cs(0.1)FA(0.9)PbI(3) has been investigated by neutron powder diffraction (NPD), complemented by single crystal and power X-ray diffraction and photoluminescence spectroscopy. The Cs-substitution limit has been determined to be less than 15%, and the cubic alpha-phase, Cs(0.1)FA(0.9)PbI(3), is shown to be synthesizable in bulk and stable at 300 K. On cooling the cubic Cs(0.1)FA(0.9)PbI(3), a slow, second-order cubic to tetragonal transition is observed close to 290 K, with variable temperature NPD indicating the presence of the tetragonal beta-phase, adopting the space group P4/mbm between 290 and 180 K. An orthorhombic phase or twinned tetragonal phase is formed below 180 K, and the temperature for further transition to a disordered state is lowered to 125 K compared to that seen in phase pure alpha-FAPbI(3) (140 K). These results demonstrate the importance of understanding the effect of cation site substitution on structure-property relationships in perovskite materials.
9.
H Huang, L Wu, Y Wang, A F Richter, M Döblinger, J Feldmann
Facile Synthesis of FAPbI3 Nanorods Journal Article
In: Nanomaterials, vol. 10, no. 1, pp. 72, 2019, ISSN: 2079-4991.
@article{,
title = {Facile Synthesis of FAPbI3 Nanorods},
author = {H Huang and L Wu and Y Wang and A F Richter and M D\"{o}blinger and J Feldmann},
url = {https://www.mdpi.com/2079-4991/10/1/72},
issn = {2079-4991},
year = {2019},
date = {2019-12-29},
journal = {Nanomaterials},
volume = {10},
number = {1},
pages = {72},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
8.
S Rieger, B J Bohn, M Doblinger, A F Richter, Y Tong, K Wang, P Muller-Buschbaum, L Polavarapu, L Leppert, J K Stolarczyk, J Feldmann
Excitons and narrow bands determine the optical properties of cesium bismuth halides Journal Article
In: Physical Review B, vol. 100, no. 20, 2019, ISSN: 2469-9950.
@article{,
title = {Excitons and narrow bands determine the optical properties of cesium bismuth halides},
author = {S Rieger and B J Bohn and M Doblinger and A F Richter and Y Tong and K Wang and P Muller-Buschbaum and L Polavarapu and L Leppert and J K Stolarczyk and J Feldmann},
url = {\<Go to ISI\>://WOS:000498055800001},
doi = {10.1103/PhysRevB.100.201404},
issn = {2469-9950},
year = {2019},
date = {2019-11-20},
journal = {Physical Review B},
volume = {100},
number = {20},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
7.
L Janker, Y Tong, L Polavarapu, J Feldmann, A S Urban, H J Krenner
Real-Time Electron and Hole Transport Dynamics in Halide Perovskite Nanowires Journal Article
In: Nano Letters, vol. 19, no. 12, pp. 8701-8707, 2019, ISSN: 1530-6984.
@article{,
title = {Real-Time Electron and Hole Transport Dynamics in Halide Perovskite Nanowires},
author = {L Janker and Y Tong and L Polavarapu and J Feldmann and A S Urban and H J Krenner},
url = {\<Go to ISI\>://WOS:000502687500044},
doi = {10.1021/acs.nanolett.9b03396},
issn = {1530-6984},
year = {2019},
date = {2019-10-30},
journal = {Nano Letters},
volume = {19},
number = {12},
pages = {8701-8707},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
6.
L Polavarapu, H Huang, Y Li, Y Tong, E-P Yao, M Döblinger, M W Feil, A F Richter, A L Rogach, J Feldmann
Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-controlled Synthesis Journal Article
In: Angewandte Chemie International Edition, vol. 0, no. ja, 2019, ISSN: 1433-7851.
@article{,
title = {Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-controlled Synthesis},
author = {L Polavarapu and H Huang and Y Li and Y Tong and E-P Yao and M D\"{o}blinger and M W Feil and A F Richter and A L Rogach and J Feldmann},
url = {https://doi.org/10.1002/anie.201906862},
doi = {10.1002/anie.201906862},
issn = {1433-7851},
year = {2019},
date = {2019-08-21},
journal = {Angewandte Chemie International Edition},
volume = {0},
number = {ja},
abstract = {The growing demand of perovskite nanocrystals (NCs) for various applications has stimulated great research interest in the development of facile synthetic methods. They have often been synthesized by either ligand assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP effects their stability. Herein, we report on the spontaneous crystallization of perovskite nanocrystals in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without applying any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+) and Cs+) to divalent (Pb2+) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and can be generally applicable for perovskite NCs of different compositions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The growing demand of perovskite nanocrystals (NCs) for various applications has stimulated great research interest in the development of facile synthetic methods. They have often been synthesized by either ligand assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP effects their stability. Herein, we report on the spontaneous crystallization of perovskite nanocrystals in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without applying any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+) and Cs+) to divalent (Pb2+) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and can be generally applicable for perovskite NCs of different compositions.
5.
Y X Li, H Huang, Y Xiong, A F Richter, S V Kershaw, J Feldmann, A L Rogach
Using Polar Alcohols for the Direct Synthesis of Cesium Lead Halide Perovskite Nanorods with Anisotropic Emission Journal Article
In: Acs Nano, vol. 13, no. 7, pp. 8237-8245, 2019, ISSN: 1936-0851.
@article{,
title = {Using Polar Alcohols for the Direct Synthesis of Cesium Lead Halide Perovskite Nanorods with Anisotropic Emission},
author = {Y X Li and H Huang and Y Xiong and A F Richter and S V Kershaw and J Feldmann and A L Rogach},
url = {\<Go to ISI\>://WOS:000477786400088},
doi = {10.1021/acsnano.9b03508},
issn = {1936-0851},
year = {2019},
date = {2019-07-11},
journal = {Acs Nano},
volume = {13},
number = {7},
pages = {8237-8245},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
4.
A Mähringer, A C Jakowetz, J M Rotter, B J Bohn, J K Stolarczyk, J Feldmann, T Bein, D D Medina
Oriented Thin Films of Electroactive Triphenylene Catecholate-Based Two-Dimensional Metal–Organic Frameworks Journal Article
In: ACS Nano, vol. 13, no. 6, pp. 6711-6719, 2019, ISSN: 1936-0851.
@article{nokey,
title = {Oriented Thin Films of Electroactive Triphenylene Catecholate-Based Two-Dimensional Metal\textendashOrganic Frameworks},
author = {A M\"{a}hringer and A C Jakowetz and J M Rotter and B J Bohn and J K Stolarczyk and J Feldmann and T Bein and D D Medina},
url = {https://doi.org/10.1021/acsnano.9b01137},
doi = {10.1021/acsnano.9b01137},
issn = {1936-0851},
year = {2019},
date = {2019-05-02},
journal = {ACS Nano},
volume = {13},
number = {6},
pages = {6711-6719},
abstract = {Two-dimensional triphenylene-based metal\textendashorganic frameworks (TP-MOFs) attract significant scientific interest due to their long-range order combined with significant electrical conductivity. The deposition of these structures as oriented films is expected to promote their incorporation into diverse optoelectronic devices. However, to date, a controlled deposition strategy applicable for the different members of this MOF family has not been reported yet. Herein, we present the synthesis of highly oriented thin films of TP-MOFs by vapor-assisted conversion (VAC). We targeted the M-CAT-1 series comprising hexahydroxytriphenylene organic ligands and metal-ions such as Ni2+, Co2+, and Cu2+. These planar organic building blocks are connected in-plane to the metal-ions through a square planar node forming extended sheets which undergo self-organization into defined stacks. Highly oriented thin Ni- and Co-CAT-1 films grown on gold substrates feature a high surface coverage with a uniform film topography and thickness ranging from 180 to 200 nm. The inclusion of acid modulators in the synthesis enabled the growth of films with a preferred orientation on quartz and on conductive substrates such as indium-doped tin oxide (ITO). The van der Pauw measurements performed across the M-CAT-1 films revealed high electrical conductivity values of up to 10\textendash3 S cm\textendash1 for both the Ni- and Co-CAT-1 films. Films grown on quartz allowed for a detailed photophysical characterization by means of UV\textendashvis, photoluminescence, and transient absorption spectroscopy. The latter revealed the existence of excited states on a nanosecond time scale, sufficiently long to demonstrate a photoinduced charge generation and extraction in Ni-CAT-1 films. This was achieved by fabricating a basic photovoltaic device with an ITO/Ni-CAT-1/Al architecture, thus establishing this MOF as a photoactive material. Our results point to the intriguing capabilities of these conductive M-CAT-1 materials and an additional scope of applications as photoabsorbers enabled through VAC thin-film synthesis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional triphenylene-based metal–organic frameworks (TP-MOFs) attract significant scientific interest due to their long-range order combined with significant electrical conductivity. The deposition of these structures as oriented films is expected to promote their incorporation into diverse optoelectronic devices. However, to date, a controlled deposition strategy applicable for the different members of this MOF family has not been reported yet. Herein, we present the synthesis of highly oriented thin films of TP-MOFs by vapor-assisted conversion (VAC). We targeted the M-CAT-1 series comprising hexahydroxytriphenylene organic ligands and metal-ions such as Ni2+, Co2+, and Cu2+. These planar organic building blocks are connected in-plane to the metal-ions through a square planar node forming extended sheets which undergo self-organization into defined stacks. Highly oriented thin Ni- and Co-CAT-1 films grown on gold substrates feature a high surface coverage with a uniform film topography and thickness ranging from 180 to 200 nm. The inclusion of acid modulators in the synthesis enabled the growth of films with a preferred orientation on quartz and on conductive substrates such as indium-doped tin oxide (ITO). The van der Pauw measurements performed across the M-CAT-1 films revealed high electrical conductivity values of up to 10–3 S cm–1 for both the Ni- and Co-CAT-1 films. Films grown on quartz allowed for a detailed photophysical characterization by means of UV–vis, photoluminescence, and transient absorption spectroscopy. The latter revealed the existence of excited states on a nanosecond time scale, sufficiently long to demonstrate a photoinduced charge generation and extraction in Ni-CAT-1 films. This was achieved by fabricating a basic photovoltaic device with an ITO/Ni-CAT-1/Al architecture, thus establishing this MOF as a photoactive material. Our results point to the intriguing capabilities of these conductive M-CAT-1 materials and an additional scope of applications as photoabsorbers enabled through VAC thin-film synthesis.
3.
R L Z Hoye, M L Lai, M Anaya, Y Tong, K Galkowski, T Doherty, W W Li, T N Huq, S Mackowski, L Polavarapu, J Feldmann, J L Macmanus-Driscoll, R H Friend, A S Urban, S D Stranks
In: Acs Energy Letters, vol. 4, no. 5, pp. 1181-1188, 2019, ISSN: 2380-8195.
@article{,
title = {Identifying and Reducing Interfacial Losses to Enhance Color-Pure Electroluminescence in Blue-Emitting Perovskite Nanoplatelet Light-Emitting Diodes},
author = {R L Z Hoye and M L Lai and M Anaya and Y Tong and K Galkowski and T Doherty and W W Li and T N Huq and S Mackowski and L Polavarapu and J Feldmann and J L Macmanus-Driscoll and R H Friend and A S Urban and S D Stranks},
url = {\<Go to ISI\>://WOS:000468015600025},
doi = {10.1021/acsenergylett.9b00571},
issn = {2380-8195},
year = {2019},
date = {2019-04-17},
journal = {Acs Energy Letters},
volume = {4},
number = {5},
pages = {1181-1188},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2.
J A Sichert, A Hemmerling, C Cardenas-Daw, A S Urban, J Feldmann
Tuning the optical bandgap in layered hybrid perovskites through variation of alkyl chain length Journal Article
In: Apl Materials, vol. 7, no. 4, 2019, ISSN: 2166-532X.
@article{,
title = {Tuning the optical bandgap in layered hybrid perovskites through variation of alkyl chain length},
author = {J A Sichert and A Hemmerling and C Cardenas-Daw and A S Urban and J Feldmann},
url = {\<Go to ISI\>://WOS:000466615300017},
doi = {10.1063/1.5087296},
issn = {2166-532X},
year = {2019},
date = {2019-04-16},
journal = {Apl Materials},
volume = {7},
number = {4},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
1.
E-P Yao, B J Bohn, Y Tong, H Huang, L Polavarapu, J Feldmann
Exciton Diffusion Lengths and Dissociation Rates in CsPbBr3 Nanocrystal–Fullerene Composites: Layer-by-Layer versus Blend Structures Journal Article
In: Advanced Optical Materials, vol. 7, no. 8, pp. 1801776, 2019, ISSN: 2195-1071.
@article{,
title = {Exciton Diffusion Lengths and Dissociation Rates in CsPbBr3 Nanocrystal\textendashFullerene Composites: Layer-by-Layer versus Blend Structures},
author = {E-P Yao and B J Bohn and Y Tong and H Huang and L Polavarapu and J Feldmann},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201801776},
doi = {10.1002/adom.201801776},
issn = {2195-1071},
year = {2019},
date = {2019-02-18},
journal = {Advanced Optical Materials},
volume = {7},
number = {8},
pages = {1801776},
abstract = {Abstract Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness of the NC layer on top of the PCBM in the layer-by-layer heterostructure, an exciton diffusion length of 290 ± 28 nm for CsPbBr3 NC is extracted. The diffusion process is followed by an ultrafast exciton dissociation (within 200 fs) at the CsPbBr3 NC/PCBM interface. In blend structures an overall faster charge transfer process is observed. Furthermore, photoconductivity measurements on a blend structure-based photodetector reveal an effective charge extraction from the active layer resulting in a high photosensitivity. DT measurements on this blend structure including adjacent electron- or hole-transport layers give insight into the extraction process and suggest a certain degree of phase segregation, which assists the charge collection.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness of the NC layer on top of the PCBM in the layer-by-layer heterostructure, an exciton diffusion length of 290 ± 28 nm for CsPbBr3 NC is extracted. The diffusion process is followed by an ultrafast exciton dissociation (within 200 fs) at the CsPbBr3 NC/PCBM interface. In blend structures an overall faster charge transfer process is observed. Furthermore, photoconductivity measurements on a blend structure-based photodetector reveal an effective charge extraction from the active layer resulting in a high photosensitivity. DT measurements on this blend structure including adjacent electron- or hole-transport layers give insight into the extraction process and suggest a certain degree of phase segregation, which assists the charge collection.