7.
R Shafei, A Hamano, C Gourlaouen, D Maganas, K Takano, C Daniel, F Neese
In: The Journal of Chemical Physics, vol. 159, no. 8, 0000, ISSN: 0021-9606.
Abstract | Links | Tags: Foundry Organic, Solid-Liquid
@article{nokey,
title = {Theoretical spectroscopy for unraveling the intensity mechanism of the optical and photoluminescent spectra of chiral Re(I) transition metal complexes},
author = {R Shafei and A Hamano and C Gourlaouen and D Maganas and K Takano and C Daniel and F Neese},
url = {https://doi.org/10.1063/5.0153742},
doi = {10.1063/5.0153742},
issn = {0021-9606},
journal = {The Journal of Chemical Physics},
volume = {159},
number = {8},
abstract = {In this work, we present a computational study that is able to predict the optical absorption and photoluminescent properties of the chiral Re(I) family of complexes [fac-ReX(CO)3L], where X is either Cl or I and L is N-heterocyclic carbene extended with π-conjugated [5]-helicenic unit. The computational strategy is based on carefully calibrated time dependent density functional theory calculations and operates in conjunction with an excited state dynamics approach to treat in addition to absorption (ABS) and photoluminescence (PL), electronic circular dichroism (ECD), and circularly polarized luminescence (CPL) spectroscopies, respectively. The employed computational approach provides, an addition, access to the computation of phosphorescence rates in terms of radiative and non-radiative relaxation processes. The chosen molecules consist of representative examples of non-helicenic (NHC) and helicenic diastereomers. The agreement between theoretical and experimental spectra, including absorption (ABS, ECD) and emission (PL, CPL), is excellent, validating a quantitative interpretation of the spectral features on the basis of natural transition orbitals and TheoDore analyses. It is demonstrated that across the set of studied Re(I) diastereomers, the emission process in the case of NHC diastereomers is metal to ligand charge transfer in nature and is dominated by the easy-axis anisotropy of the emissive excited multiplet. On the contrary, in the cases of the helicenic diastereomers, the emission process is intra ligand charge transfer in nature and is dominated by the respective easy-plane anisotropy of the emissive excited multiplet. This affects remarkably the photoluminescent properties of the molecules in terms of PL and CPL spectral band shapes, spin-vibronic coupling, relaxation times, and the respective quantum yields. Spin-vibronic coupling effects are investigated at the level of the state-average complete active space self-consistent field in conjunction with quasi-degenerate second order perturbation theory. It is in fact demonstrated that a spin-vibronic coupling mechanism controls the observed photophysics of this class of Re(I) complexes.},
keywords = {Foundry Organic, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
In this work, we present a computational study that is able to predict the optical absorption and photoluminescent properties of the chiral Re(I) family of complexes [fac-ReX(CO)3L], where X is either Cl or I and L is N-heterocyclic carbene extended with π-conjugated [5]-helicenic unit. The computational strategy is based on carefully calibrated time dependent density functional theory calculations and operates in conjunction with an excited state dynamics approach to treat in addition to absorption (ABS) and photoluminescence (PL), electronic circular dichroism (ECD), and circularly polarized luminescence (CPL) spectroscopies, respectively. The employed computational approach provides, an addition, access to the computation of phosphorescence rates in terms of radiative and non-radiative relaxation processes. The chosen molecules consist of representative examples of non-helicenic (NHC) and helicenic diastereomers. The agreement between theoretical and experimental spectra, including absorption (ABS, ECD) and emission (PL, CPL), is excellent, validating a quantitative interpretation of the spectral features on the basis of natural transition orbitals and TheoDore analyses. It is demonstrated that across the set of studied Re(I) diastereomers, the emission process in the case of NHC diastereomers is metal to ligand charge transfer in nature and is dominated by the easy-axis anisotropy of the emissive excited multiplet. On the contrary, in the cases of the helicenic diastereomers, the emission process is intra ligand charge transfer in nature and is dominated by the respective easy-plane anisotropy of the emissive excited multiplet. This affects remarkably the photoluminescent properties of the molecules in terms of PL and CPL spectral band shapes, spin-vibronic coupling, relaxation times, and the respective quantum yields. Spin-vibronic coupling effects are investigated at the level of the state-average complete active space self-consistent field in conjunction with quasi-degenerate second order perturbation theory. It is in fact demonstrated that a spin-vibronic coupling mechanism controls the observed photophysics of this class of Re(I) complexes.
6.
A Stadlbauer, L Eyre, A Biewald, F Rauh, M W Heindl, S Liu, J Zerhoch, S Feldmann, A Hartschuh, F Deschler
Photoexcitation Control of Excitation Relaxation in Mixed-Phase Ruddlesden-Popper Hybrid Organic-Inorganic Lead-Iodide Perovskites Journal Article
In: Advanced Optical Materials, vol. n/a, no. n/a, pp. 2301331, 0000, ISSN: 2195-1071.
Abstract | Links | Tags: Molecularly-Functionalized, Solid-Liquid
@article{nokey,
title = {Photoexcitation Control of Excitation Relaxation in Mixed-Phase Ruddlesden-Popper Hybrid Organic-Inorganic Lead-Iodide Perovskites},
author = {A Stadlbauer and L Eyre and A Biewald and F Rauh and M W Heindl and S Liu and J Zerhoch and S Feldmann and A Hartschuh and F Deschler},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202301331},
doi = {https://doi.org/10.1002/adom.202301331},
issn = {2195-1071},
journal = {Advanced Optical Materials},
volume = {n/a},
number = {n/a},
pages = {2301331},
abstract = {Abstract The electronic states and exciton binding energies of layered Ruddlesden-Popper (RP) metal-halide perovskites can be tailored through changes of their chemical composition, yielding multi-phase systems with complex energy cascades. Ultrafast photoexcitation relaxation with transfer dynamics into domains of increasing layer number has been reported for these materials. Here, ultrafast optical spectroscopy is used to report an unexpected excitation energy dependence of photoexcitation relaxation dynamics in mixed-dimensional benzylammonium cesium lead iodide RP perovskite (BeA2CsPb2I7) thin films, which gives rise to spectrally broadband luminescence over the visible region. Using transient absorption and photoluminescence spectroscopy it is found that excitations, which are formed in the n = 2 RP-phase after photoexcitation with ≈0.2 electron volt excess energy, transfer to higher layer number RP-phases on unexpectedly slow timescales of tens of picoseconds. Further, it is observed that such excitations are initially optically passive. Notably, luminescence occurs under these conditions from multiple RP-phases with optical bandgaps across the visible range, yielding broadband luminescence. The results hold potential for realization of broadband white-light emitters and other light-emitting devices.},
keywords = {Molecularly-Functionalized, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
Abstract The electronic states and exciton binding energies of layered Ruddlesden-Popper (RP) metal-halide perovskites can be tailored through changes of their chemical composition, yielding multi-phase systems with complex energy cascades. Ultrafast photoexcitation relaxation with transfer dynamics into domains of increasing layer number has been reported for these materials. Here, ultrafast optical spectroscopy is used to report an unexpected excitation energy dependence of photoexcitation relaxation dynamics in mixed-dimensional benzylammonium cesium lead iodide RP perovskite (BeA2CsPb2I7) thin films, which gives rise to spectrally broadband luminescence over the visible region. Using transient absorption and photoluminescence spectroscopy it is found that excitations, which are formed in the n = 2 RP-phase after photoexcitation with ≈0.2 electron volt excess energy, transfer to higher layer number RP-phases on unexpectedly slow timescales of tens of picoseconds. Further, it is observed that such excitations are initially optically passive. Notably, luminescence occurs under these conditions from multiple RP-phases with optical bandgaps across the visible range, yielding broadband luminescence. The results hold potential for realization of broadband white-light emitters and other light-emitting devices.
5.
T Tian, S Tu, A Xu, S Yin, A L Oechsle, T Xiao, A Vagias, J Eichhorn, J Suo, Z Yang, S Bernstorff, P Müller-Buschbaum
Unraveling the Morphology-Function Correlation of Mesoporous ZnO Films upon Water Exposure Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2311793, 0000, ISSN: 1616-301X.
Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid
@article{nokey,
title = {Unraveling the Morphology-Function Correlation of Mesoporous ZnO Films upon Water Exposure},
author = {T Tian and S Tu and A Xu and S Yin and A L Oechsle and T Xiao and A Vagias and J Eichhorn and J Suo and Z Yang and S Bernstorff and P M\"{u}ller-Buschbaum},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202311793},
doi = {https://doi.org/10.1002/adfm.202311793},
issn = {1616-301X},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2311793},
abstract = {Abstract Ubiquitous moisture in synthetic conditions and ambient environments can strongly influence the conductivity of ZnO semiconductors via the chemisorption and physisorption of water molecules on the ZnO surface. Such an intrinsically water-sensitive nature will become more evident in mesoporous ZnO films where a large surface area and active sites are created simultaneously. However, fundamental insights underlying water-mediated ZnO surface chemistry and electrical conductivity and the factors affecting them remain ambiguous due to the complexity of ZnO surfaces and the difficulties of in situ characterizations at multi-dimensions. Here, self-assembling diblock copolymers are exploited as structure-directing agents to achieve mesoporous ZnO thin films with highly tailorable structural characteristics ranging from nanomorphologies, over crystalline levels, to defect contents. As verified by theoretical calculations, the presence of oxygen vacancy will facilitate favorable water adsorption and subsequent dissociation on the polar ZnO surfaces. Upon humidity exposure with progressively increased levels, mesoporous ZnO films are revealed to follow an almost positive relationship between adsorption and electrical conductivity but show superior morphological stability. This work not only elucidates the water-governed ZnO surface chemistry but may also promote a comprehensive understanding of the morphology-function relationship on ZnO-based electronics.},
keywords = {Foundry Inorganic, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
Abstract Ubiquitous moisture in synthetic conditions and ambient environments can strongly influence the conductivity of ZnO semiconductors via the chemisorption and physisorption of water molecules on the ZnO surface. Such an intrinsically water-sensitive nature will become more evident in mesoporous ZnO films where a large surface area and active sites are created simultaneously. However, fundamental insights underlying water-mediated ZnO surface chemistry and electrical conductivity and the factors affecting them remain ambiguous due to the complexity of ZnO surfaces and the difficulties of in situ characterizations at multi-dimensions. Here, self-assembling diblock copolymers are exploited as structure-directing agents to achieve mesoporous ZnO thin films with highly tailorable structural characteristics ranging from nanomorphologies, over crystalline levels, to defect contents. As verified by theoretical calculations, the presence of oxygen vacancy will facilitate favorable water adsorption and subsequent dissociation on the polar ZnO surfaces. Upon humidity exposure with progressively increased levels, mesoporous ZnO films are revealed to follow an almost positive relationship between adsorption and electrical conductivity but show superior morphological stability. This work not only elucidates the water-governed ZnO surface chemistry but may also promote a comprehensive understanding of the morphology-function relationship on ZnO-based electronics.
4.
R Tripathi, G Yesilbas, X Lamprecht, P Gandharapu, A S Bandarenka, R O Dusane, A Mukhopadhyay
In: Journal of The Electrochemical Society, vol. 170, no. 9, pp. 090544, 0000, ISSN: 1945-7111 0013-4651.
Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid
@article{nokey,
title = {Understanding the Electrolyte Chemistry Induced Enhanced Stability of Si Anodes in Li-Ion Batteries based on Physico-Chemical Changes, Impedance, and Stress Evolution during SEI Formation},
author = {R Tripathi and G Yesilbas and X Lamprecht and P Gandharapu and A S Bandarenka and R O Dusane and A Mukhopadhyay},
url = {https://dx.doi.org/10.1149/1945-7111/acfb3f},
doi = {10.1149/1945-7111/acfb3f},
issn = {1945-7111
0013-4651},
journal = {Journal of The Electrochemical Society},
volume = {170},
number = {9},
pages = {090544},
abstract = {The volume expansion/contraction of Si-based anodes during electrochemical lithiation/delithiation cycles causes a loss in mechanical integrity and accrued instability of the solid electrolyte interphase (SEI) layer, culminating into capacity fade. Electrolyte additives like fluoroethylene carbonate (FEC) improve SEI stability, but the associated causes still under debate. This work reveals some of the roles of FEC via post-mortem observations/analyses, operando stress measurements and a comprehensive study of the impedance associated with the formation/evolution of SEI during lithiation/delithiation. Usage of 10 vol.% FEC as electrolyte additive leads to significant improvements in cyclic stability, Coulombic efficiency and facilitates smoother/compact/crack-free surface/SEI, in contrast to the cracked/pitted/uneven surface upon non-usage of FEC. Operando stress measurements during SEI formation reveal compressive stress development, followed by loss in mechanical integrity, upon non-usage of electrolyte additive, in contrast to insignificant stress development associated with SEI formation upon usage of FEC. The EIS model proposed here facilitates good fit with the impedance data at all states-of-charges, with the SEI resistance and capacitance exhibiting expected variations with cycling and the SEI resistance progressively decreasing with cycle number in the presence of FEC. By contrast, in the absence of FEC, severe fluctuations observed with the SEI resistance and capacitance indicate instability.},
keywords = {Foundry Inorganic, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
The volume expansion/contraction of Si-based anodes during electrochemical lithiation/delithiation cycles causes a loss in mechanical integrity and accrued instability of the solid electrolyte interphase (SEI) layer, culminating into capacity fade. Electrolyte additives like fluoroethylene carbonate (FEC) improve SEI stability, but the associated causes still under debate. This work reveals some of the roles of FEC via post-mortem observations/analyses, operando stress measurements and a comprehensive study of the impedance associated with the formation/evolution of SEI during lithiation/delithiation. Usage of 10 vol.% FEC as electrolyte additive leads to significant improvements in cyclic stability, Coulombic efficiency and facilitates smoother/compact/crack-free surface/SEI, in contrast to the cracked/pitted/uneven surface upon non-usage of FEC. Operando stress measurements during SEI formation reveal compressive stress development, followed by loss in mechanical integrity, upon non-usage of electrolyte additive, in contrast to insignificant stress development associated with SEI formation upon usage of FEC. The EIS model proposed here facilitates good fit with the impedance data at all states-of-charges, with the SEI resistance and capacitance exhibiting expected variations with cycling and the SEI resistance progressively decreasing with cycle number in the presence of FEC. By contrast, in the absence of FEC, severe fluctuations observed with the SEI resistance and capacitance indicate instability.
3.
L I Wagner, E Sirotti, O Brune, G Grötzner, J Eichhorn, S Santra, F Munnik, L Olivi, S Pollastri, V Streibel, I D Sharp
Defect Engineering of Ta3N5 Photoanodes: Enhancing Charge Transport and Photoconversion Efficiencies via Ti Doping Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2306539, 0000, ISSN: 1616-301X.
Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid
@article{nokey,
title = {Defect Engineering of Ta3N5 Photoanodes: Enhancing Charge Transport and Photoconversion Efficiencies via Ti Doping},
author = {L I Wagner and E Sirotti and O Brune and G Gr\"{o}tzner and J Eichhorn and S Santra and F Munnik and L Olivi and S Pollastri and V Streibel and I D Sharp},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202306539},
doi = {https://doi.org/10.1002/adfm.202306539},
issn = {1616-301X},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2306539},
abstract = {Abstract While Ta3N5 shows excellent potential as a semiconductor photoanode for solar water splitting, its performance is hindered by poor charge carrier transport and trapping due to native defects that introduce electronic states deep within its bandgap. Here, it is demonstrated that controlled Ti doping of Ta3N5 can dramatically reduce the concentration of deep-level defects and enhance its photoelectrochemical performance, yielding a sevenfold increase in photocurrent density and a 300 mV cathodic shift in photocurrent onset potential compared to undoped material. Comprehensive characterization reveals that Ti4+ ions substitute Ta5+ lattice sites, thereby introducing compensating acceptor states, reducing the concentrations of deleterious nitrogen vacancies and reducing Ta3+ states, and thereby suppressing trapping and recombination. Owing to the similar ionic radii of Ti4+ and Ta5+, substitutional doping does not introduce lattice strain or significantly affect the underlying electronic structure of the host semiconductor. Furthermore, Ti can be incorporated without increasing the oxygen donor content, thereby enabling the electrical conductivity to be tuned by over seven orders of magnitude. Thus, Ti doping of Ta3N5 provides a powerful basis for precisely engineering its optoelectronic characteristics and to substantially improve its functional characteristics as an advanced photoelectrode for solar fuels applications.},
keywords = {Foundry Inorganic, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
Abstract While Ta3N5 shows excellent potential as a semiconductor photoanode for solar water splitting, its performance is hindered by poor charge carrier transport and trapping due to native defects that introduce electronic states deep within its bandgap. Here, it is demonstrated that controlled Ti doping of Ta3N5 can dramatically reduce the concentration of deep-level defects and enhance its photoelectrochemical performance, yielding a sevenfold increase in photocurrent density and a 300 mV cathodic shift in photocurrent onset potential compared to undoped material. Comprehensive characterization reveals that Ti4+ ions substitute Ta5+ lattice sites, thereby introducing compensating acceptor states, reducing the concentrations of deleterious nitrogen vacancies and reducing Ta3+ states, and thereby suppressing trapping and recombination. Owing to the similar ionic radii of Ti4+ and Ta5+, substitutional doping does not introduce lattice strain or significantly affect the underlying electronic structure of the host semiconductor. Furthermore, Ti can be incorporated without increasing the oxygen donor content, thereby enabling the electrical conductivity to be tuned by over seven orders of magnitude. Thus, Ti doping of Ta3N5 provides a powerful basis for precisely engineering its optoelectronic characteristics and to substantially improve its functional characteristics as an advanced photoelectrode for solar fuels applications.
2.
G Yesilbas, C-Y Chou, A S Bandarenka
A Physical Impedance Model of Lithium Intercalation into Graphite Electrodes for a Coin-Cell Assembly Journal Article
In: ChemElectroChem, vol. 10, no. 21, pp. e202300270, 0000, ISSN: 2196-0216.
Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid
@article{nokey,
title = {A Physical Impedance Model of Lithium Intercalation into Graphite Electrodes for a Coin-Cell Assembly},
author = {G Yesilbas and C-Y Chou and A S Bandarenka},
url = {https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/celc.202300270},
doi = {https://doi.org/10.1002/celc.202300270},
issn = {2196-0216},
journal = {ChemElectroChem},
volume = {10},
number = {21},
pages = {e202300270},
abstract = {Abstract Graphite electrodes are widely used in commercial metal-ion batteries as anodes. Electrochemical impedance spectroscopy serves as one of the primary non-destructive techniques to obtain key information about various batteries during their operation. However, interpretation of the impedance response of graphite electrodes in contact with common organic electrolytes can be complicated. It is especially challenging, particularly when utilizing the 2-electrode configuration that is common in battery research. In this work, we elaborate on a physical impedance model capable of accurately describing the impedance spectra of a graphite|electrolyte|metallic Li system in a coin-cell assembly during two initial charge/discharge cycles. We analyze the dependencies of the model parameters for graphite and metallic lithium as a function of the state of charge to verify the model. Additionally, we suggest that the double layer capacitance values obtained during specific intercalation stages could help to determine if the area-normalized values align with the expected range. The data and the procedure necessary for calibration are provided.},
keywords = {Foundry Inorganic, Solid-Liquid},
pubstate = {published},
tppubtype = {article}
}
Abstract Graphite electrodes are widely used in commercial metal-ion batteries as anodes. Electrochemical impedance spectroscopy serves as one of the primary non-destructive techniques to obtain key information about various batteries during their operation. However, interpretation of the impedance response of graphite electrodes in contact with common organic electrolytes can be complicated. It is especially challenging, particularly when utilizing the 2-electrode configuration that is common in battery research. In this work, we elaborate on a physical impedance model capable of accurately describing the impedance spectra of a graphite|electrolyte|metallic Li system in a coin-cell assembly during two initial charge/discharge cycles. We analyze the dependencies of the model parameters for graphite and metallic lithium as a function of the state of charge to verify the model. Additionally, we suggest that the double layer capacitance values obtained during specific intercalation stages could help to determine if the area-normalized values align with the expected range. The data and the procedure necessary for calibration are provided.
1.
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, 0000, ISSN: 2211-2855.
Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid
@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},
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 = {Foundry Inorganic, Solid-Liquid},
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.