Prof. Dr. Hubert Ebert
Fields of Application
Publications
14.
F Wolf, T Chau, D Han, K B Spooner, M Righetto, P Dörflinger, S Wang, R Guntermann, R Hooijer, D O Scanlon, H Ebert, V Dyakonov, L M Herz, T Bein
In: Journal of the American Chemical Society, vol. 147, no. 20, pp. 16992-17001, 2025, ISSN: 0002-7863.
@article{nokey,
title = {Oriented Naphthalene-O-propylammonium-Based (NOP)4AuBIIII8 (B = Au, Bi, Sb) Ruddlesden\textendashPopper Two-Dimensional Gold Double Perovskite Thin Films Featuring High Charge-Carrier Mobility},
author = {F Wolf and T Chau and D Han and K B Spooner and M Righetto and P D\"{o}rflinger and S Wang and R Guntermann and R Hooijer and D O Scanlon and H Ebert and V Dyakonov and L M Herz and T Bein},
url = {https://doi.org/10.1021/jacs.5c01102},
doi = {10.1021/jacs.5c01102},
issn = {0002-7863},
year = {2025},
date = {2025-05-21},
journal = {Journal of the American Chemical Society},
volume = {147},
number = {20},
pages = {16992-17001},
abstract = {Two-dimensional perovskites show intriguing optoelectronic properties due to their anisotropic structure and multiple quantum well structure. Here, we report the first three gold-based Ruddlesden\textendashPopper type two-dimensional double perovskites with a general formula (NOP)4AuIBIIII8 (B = Au, Bi, Sb) employing naphthalene-O-propylammonium (NOP) as an organic cation. They were found to form highly crystalline thin films on various substrates, predominantly oriented in the [001] direction featuring continuous, crack-free film areas on the μm2 scale. The thin films show strong optical absorption in the visible region, with band gap energies between 1.48 and 2.32 eV. Density functional theory calculations support the experimentally obtained band gap energies and predict high charge-carrier mobilities and effective charge separation. A comprehensive study with time-resolved microwave conductivity (TRMC) and optical-pump-THz-probe (OPTP) spectroscopy revealed high charge-carrier mobilities for lead-free two-dimensional perovskites of 4.0 ± 0.2 cm2(V s)−1 and charge-carrier lifetimes in the range of μs. Photoconductivity measurements under 1 sun illumination demonstrated the material’s application as a photodetector, showing a 2-fold increase in conductivity when exposed to light.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional perovskites show intriguing optoelectronic properties due to their anisotropic structure and multiple quantum well structure. Here, we report the first three gold-based Ruddlesden–Popper type two-dimensional double perovskites with a general formula (NOP)4AuIBIIII8 (B = Au, Bi, Sb) employing naphthalene-O-propylammonium (NOP) as an organic cation. They were found to form highly crystalline thin films on various substrates, predominantly oriented in the [001] direction featuring continuous, crack-free film areas on the μm2 scale. The thin films show strong optical absorption in the visible region, with band gap energies between 1.48 and 2.32 eV. Density functional theory calculations support the experimentally obtained band gap energies and predict high charge-carrier mobilities and effective charge separation. A comprehensive study with time-resolved microwave conductivity (TRMC) and optical-pump-THz-probe (OPTP) spectroscopy revealed high charge-carrier mobilities for lead-free two-dimensional perovskites of 4.0 ± 0.2 cm2(V s)−1 and charge-carrier lifetimes in the range of μs. Photoconductivity measurements under 1 sun illumination demonstrated the material’s application as a photodetector, showing a 2-fold increase in conductivity when exposed to light.
13.
T G Chau, D Han, F Wolf, S S Rudel, Y Yao, H Oberhofer, T Bein, H Ebert, W Schnick
Defect Imide Double Antiperovskites AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi) as Potential Solar Cell Absorber Materials Journal Article
In: Angewandte Chemie International Edition, vol. 64, no. 17, pp. e202500768, 2025, ISSN: 1433-7851.
@article{nokey,
title = {Defect Imide Double Antiperovskites AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi) as Potential Solar Cell Absorber Materials},
author = {T G Chau and D Han and F Wolf and S S Rudel and Y Yao and H Oberhofer and T Bein and H Ebert and W Schnick},
url = {https://doi.org/10.1002/anie.202500768},
doi = {https://doi.org/10.1002/anie.202500768},
issn = {1433-7851},
year = {2025},
date = {2025-04-17},
journal = {Angewandte Chemie International Edition},
volume = {64},
number = {17},
pages = {e202500768},
abstract = {Abstract An abundance of oxide, halide and chalcogenide perovskites have been explored, demonstrating outstanding properties, while the emerging nitride perovskites are extremely rare due to their challenging synthesis requirements. By inverting the ion type in the perovskite structure, the corresponding antiperovskite structure is obtained. Among them, ternary antiperovskite nitrides X3AN (X=Ba, Sr, Ca, Mg; A=As, Sb) have recently been identified as exhibiting excellent optoelectronic properties. To explore the unrealized composition space of nitride perovskites, the ammonothermal method was applied, yielding three new layered quaternary imide-based defect-antiperovskites, namely AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi). These new compounds feature distorted square-pyramidal coordination around the imide-group (Ca5NH). Layers with Ca2+ vacancies are found with an alternating As3? and Pn3? (Pn3?=Sb3?, Bi3?) coordination along the A-site, forming a two-dimensional (2D) structure. All three AE5AsPn(NH)2 compounds show suitable direct band gaps within the visible light spectrum. Density functional theory calculations reveal favorable band dispersion, as well as transport and optical properties, especially along the out-of-plane direction, demonstrating their 3D character of electronic transport. The narrow tunable direct band gaps and favorable charge carrier properties make AE5AsPn(NH)2 promising candidates for solar cell absorber materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract An abundance of oxide, halide and chalcogenide perovskites have been explored, demonstrating outstanding properties, while the emerging nitride perovskites are extremely rare due to their challenging synthesis requirements. By inverting the ion type in the perovskite structure, the corresponding antiperovskite structure is obtained. Among them, ternary antiperovskite nitrides X3AN (X=Ba, Sr, Ca, Mg; A=As, Sb) have recently been identified as exhibiting excellent optoelectronic properties. To explore the unrealized composition space of nitride perovskites, the ammonothermal method was applied, yielding three new layered quaternary imide-based defect-antiperovskites, namely AE5AsPn(NH)2 (AE=Ca, Sr; Pn=Sb, Bi). These new compounds feature distorted square-pyramidal coordination around the imide-group (Ca5NH). Layers with Ca2+ vacancies are found with an alternating As3? and Pn3? (Pn3?=Sb3?, Bi3?) coordination along the A-site, forming a two-dimensional (2D) structure. All three AE5AsPn(NH)2 compounds show suitable direct band gaps within the visible light spectrum. Density functional theory calculations reveal favorable band dispersion, as well as transport and optical properties, especially along the out-of-plane direction, demonstrating their 3D character of electronic transport. The narrow tunable direct band gaps and favorable charge carrier properties make AE5AsPn(NH)2 promising candidates for solar cell absorber materials.
12.
R Hooijer, S Wang, A Biewald, C Eckel, M Righetto, M Chen, Z Xu, D Blätte, D Han, H Ebert, L M Herz, R T Weitz, A Hartschuh, T Bein
In: Journal of the American Chemical Society, vol. 146, no. 39, pp. 26694-26706, 2024, ISSN: 0002-7863.
@article{nokey,
title = {Overcoming Intrinsic Quantum Confinement and Ultrafast Self-Trapping in Ag\textendashBi\textendashI- and Cu\textendashBi\textendashI-Based 2D Double Perovskites through Electroactive Cations},
author = {R Hooijer and S Wang and A Biewald and C Eckel and M Righetto and M Chen and Z Xu and D Bl\"{a}tte and D Han and H Ebert and L M Herz and R T Weitz and A Hartschuh and T Bein},
url = {https://doi.org/10.1021/jacs.4c04616},
doi = {10.1021/jacs.4c04616},
issn = {0002-7863},
year = {2024},
date = {2024-10-02},
journal = {Journal of the American Chemical Society},
volume = {146},
number = {39},
pages = {26694-26706},
abstract = {The possibility to combine organic semiconducting materials with inorganic halide perovskites opens exciting pathways toward tuning optoelectronic properties. Exploring stable and nontoxic, double perovskites as a host for electroactive organic cations to form two-dimensional (2D) hybrid materials is an emerging opportunity to create both functional and lead-free materials for optoelectronic applications. By introducing naphthalene and pyrene moieties into Ag\textendashBi\textendashI and Cu\textendashBi\textendashI double perovskite lattices, intrinsic electronic challenges of double perovskites are addressed and the electronic anisotropy of 2D perovskites can be modulated. (POE)4AgBiI8 containing pyrene moieties in the 2D layers was selected from a total of eight new 2D double perovskites, exhibiting a favorable electronic band structure with a type IIb multiple quantum well system based on a layer architecture suitable for out-of-plane conductivity and leading to a photocurrent response ratio of almost 3 orders of magnitude under AM1.5G illumination. Finally, an exclusively parallelly oriented thin film of (POE)4AgBiI8 was integrated into a device to construct the first pure n = 1 Ruddlesden\textendashPopper 2D double perovskite solar cell.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The possibility to combine organic semiconducting materials with inorganic halide perovskites opens exciting pathways toward tuning optoelectronic properties. Exploring stable and nontoxic, double perovskites as a host for electroactive organic cations to form two-dimensional (2D) hybrid materials is an emerging opportunity to create both functional and lead-free materials for optoelectronic applications. By introducing naphthalene and pyrene moieties into Ag–Bi–I and Cu–Bi–I double perovskite lattices, intrinsic electronic challenges of double perovskites are addressed and the electronic anisotropy of 2D perovskites can be modulated. (POE)4AgBiI8 containing pyrene moieties in the 2D layers was selected from a total of eight new 2D double perovskites, exhibiting a favorable electronic band structure with a type IIb multiple quantum well system based on a layer architecture suitable for out-of-plane conductivity and leading to a photocurrent response ratio of almost 3 orders of magnitude under AM1.5G illumination. Finally, an exclusively parallelly oriented thin film of (POE)4AgBiI8 was integrated into a device to construct the first pure n = 1 Ruddlesden–Popper 2D double perovskite solar cell.
11.
Y Yao, D Han, K B Spooner, X Jia, H Ebert, D O Scanlon, H Oberhofer
Adapting Explainable Machine Learning to Study Mechanical Properties of 2D Hybrid Halide Perovskites Journal Article
In: Advanced Functional Materials, vol. n/a, no. n/a, pp. 2411652, 2024, ISSN: 1616-301X.
@article{nokey,
title = {Adapting Explainable Machine Learning to Study Mechanical Properties of 2D Hybrid Halide Perovskites},
author = {Y Yao and D Han and K B Spooner and X Jia and H Ebert and D O Scanlon and H Oberhofer},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202411652},
doi = {https://doi.org/10.1002/adfm.202411652},
issn = {1616-301X},
year = {2024},
date = {2024-08-13},
journal = {Advanced Functional Materials},
volume = {n/a},
number = {n/a},
pages = {2411652},
abstract = {Abstract 2D hybrid organic and inorganic perovskites (HOIPs) are used as capping layers on top of 3D perovskites to enhance their stability while maintaining the desired power conversion efficiency (PCE). Therefore, the 2D HOIP needs to withstand mechanical stresses and deformations, making the stiffness an important observable. However, there is no model for unravelling the relationship between their crystal structures and mechanical properties. In this work, explainable machine learning (ML) models are used to accelerate the in silico prediction of mechanical properties of 2D HOIPs, as indicated by their out-of-plane and in-plane Young's modulus. The ML models can distinguish between stiff and non-stiff 2D HOIPs, and extract the dominant physical feature influencing their Young's moduli, viz. the metal-halogen-metal bond angle. Furthermore, the steric effect index (STEI) of cations is found to be a rough criterion for non-stiffness. Their optimal ranges are extracted from a probability analysis. Based on the strong correlation between the deformation of octahedra and the Young's modulus, the transferability of the approach from single-layer to multi-layer 2D HOIPs is demonstrated. This work represents a step toward unravelling the complex relationship between crystal structure and mechanical properties of 2D HOIPs using ML as a tool.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract 2D hybrid organic and inorganic perovskites (HOIPs) are used as capping layers on top of 3D perovskites to enhance their stability while maintaining the desired power conversion efficiency (PCE). Therefore, the 2D HOIP needs to withstand mechanical stresses and deformations, making the stiffness an important observable. However, there is no model for unravelling the relationship between their crystal structures and mechanical properties. In this work, explainable machine learning (ML) models are used to accelerate the in silico prediction of mechanical properties of 2D HOIPs, as indicated by their out-of-plane and in-plane Young's modulus. The ML models can distinguish between stiff and non-stiff 2D HOIPs, and extract the dominant physical feature influencing their Young's moduli, viz. the metal-halogen-metal bond angle. Furthermore, the steric effect index (STEI) of cations is found to be a rough criterion for non-stiffness. Their optimal ranges are extracted from a probability analysis. Based on the strong correlation between the deformation of octahedra and the Young's modulus, the transferability of the approach from single-layer to multi-layer 2D HOIPs is demonstrated. This work represents a step toward unravelling the complex relationship between crystal structure and mechanical properties of 2D HOIPs using ML as a tool.
10.
D Han, B Zhu, Z Cai, K B Spooner, S S Rudel, W Schnick, T Bein, D O Scanlon, H Ebert
Discovery of multi-anion antiperovskites X6NFSn2 (X = Ca, Sr) as promising thermoelectric materials by computational screening Journal Article
In: Matter, vol. 7, iss. 1, pp. 158-174, 2024, ISSN: 2590-2385.
@article{nokey,
title = {Discovery of multi-anion antiperovskites X6NFSn2 (X = Ca, Sr) as promising thermoelectric materials by computational screening},
author = {D Han and B Zhu and Z Cai and K B Spooner and S S Rudel and W Schnick and T Bein and D O Scanlon and H Ebert},
url = {https://www.sciencedirect.com/science/article/pii/S2590238523005234},
doi = {https://doi.org/10.1016/j.matt.2023.10.022},
issn = {2590-2385},
year = {2024},
date = {2024-01-03},
urldate = {2024-01-03},
journal = {Matter},
volume = {7},
issue = {1},
pages = {158-174},
abstract = {Summary The thermoelectric performance of existing perovskites lags far behind that of state-of-the-art thermoelectric materials such as SnSe. Despite halide perovskites showing promising thermoelectric properties, namely, high Seebeck coefficients and ultralow thermal conductivities, their thermoelectric performance is significantly restricted by low electrical conductivities. Here, we explore new multi-anion antiperovskites X6NFSn2 (X = Ca, Sr, and Ba) via B-site anion mutation in antiperovskite and global structure searches and demonstrate their phase stability by first-principles calculations. Ca6NFSn2 and Sr6NFSn2 exhibit decent Seebeck coefficients and ultralow lattice thermal conductivities (\<1 W m−1 K−1). Notably, Ca6NFSn2 and Sr6NFSn2 show remarkably larger electrical conductivities compared to the halide perovskite CsSnI3. The combined superior electrical and thermal properties of Ca6NFSn2 and Sr6NFSn2 lead to high thermoelectric figures of merit (ZTs) of ∼1.9 and ∼2.3 at high temperatures. Our exploration of multi-anion antiperovskites X6NFSn2 (X = Ca, Sr) realizes the “phonon-glass, electron-crystal” concept within the antiperovskite structure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Summary The thermoelectric performance of existing perovskites lags far behind that of state-of-the-art thermoelectric materials such as SnSe. Despite halide perovskites showing promising thermoelectric properties, namely, high Seebeck coefficients and ultralow thermal conductivities, their thermoelectric performance is significantly restricted by low electrical conductivities. Here, we explore new multi-anion antiperovskites X6NFSn2 (X = Ca, Sr, and Ba) via B-site anion mutation in antiperovskite and global structure searches and demonstrate their phase stability by first-principles calculations. Ca6NFSn2 and Sr6NFSn2 exhibit decent Seebeck coefficients and ultralow lattice thermal conductivities (<1 W m−1 K−1). Notably, Ca6NFSn2 and Sr6NFSn2 show remarkably larger electrical conductivities compared to the halide perovskite CsSnI3. The combined superior electrical and thermal properties of Ca6NFSn2 and Sr6NFSn2 lead to high thermoelectric figures of merit (ZTs) of ∼1.9 and ∼2.3 at high temperatures. Our exploration of multi-anion antiperovskites X6NFSn2 (X = Ca, Sr) realizes the “phonon-glass, electron-crystal” concept within the antiperovskite structure.
9.
C Schröder, J Riemensberger, R Kuzian, M Ossiander, D Potamianos, F Allegrett, L Bignardi, S Lizzit, A Akil, A Cavalieri, D Menzel, S Neppl, R Ernstorfer, J Braun, H Ebert, J Minar, W Helml, M Jobst, M Gerl, E Bothschafter, A Kim, K Hütten, U Kleineberg, M Schnitzenbaumer, J V Barth, P Feulner, E Krasovskii, R Kienberger
Attosecond dynamics of photoemission over a wide photon energy range Miscellaneous
2023.
@misc{nokey,
title = {Attosecond dynamics of photoemission over a wide photon energy range},
author = {C Schr\"{o}der and J Riemensberger and R Kuzian and M Ossiander and D Potamianos and F Allegrett and L Bignardi and S Lizzit and A Akil and A Cavalieri and D Menzel and S Neppl and R Ernstorfer and J Braun and H Ebert and J Minar and W Helml and M Jobst and M Gerl and E Bothschafter and A Kim and K H\"{u}tten and U Kleineberg and M Schnitzenbaumer and J V Barth and P Feulner and E Krasovskii and R Kienberger},
url = {http://europepmc.org/abstract/PPR/PPR750080
https://doi.org/10.21203/rs.3.rs-3024896/v1},
doi = {10.21203/rs.3.rs-3024896/v1},
year = {2023},
date = {2023-10-01},
urldate = {2023-10-01},
publisher = {Research Square},
abstract = {Dynamics of photoemission from surfaces are usually studied at low photon energies (\<100 eV). Here, we report on new findings on these dynamics observed at a tungsten surface on the attosecond time scale at photon energies exceeding 100 eV, over a range of almost 50 eV. While photoemission, a fundamental process in quantum mechanics, is often described within a semiclassical three-step model, we find that even at high photon energies only a full quantum treatment in one step predicts the measured attosecond dynamics correctly. On this time scale the intuitive, mechanistic interpretation of the photoelectric effect breaks down. This underlines the necessity to further develop experimental and theoretical tools to be used in improving our understanding of the fundamental process of light-matter interaction underlying many methods in extreme ultraviolet and soft x-ray spectroscopy.},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}
Dynamics of photoemission from surfaces are usually studied at low photon energies (<100 eV). Here, we report on new findings on these dynamics observed at a tungsten surface on the attosecond time scale at photon energies exceeding 100 eV, over a range of almost 50 eV. While photoemission, a fundamental process in quantum mechanics, is often described within a semiclassical three-step model, we find that even at high photon energies only a full quantum treatment in one step predicts the measured attosecond dynamics correctly. On this time scale the intuitive, mechanistic interpretation of the photoelectric effect breaks down. This underlines the necessity to further develop experimental and theoretical tools to be used in improving our understanding of the fundamental process of light-matter interaction underlying many methods in extreme ultraviolet and soft x-ray spectroscopy.
8.
S Wang, D Han, C Maheu, Z Xu, A Biewald, H Illner, R Hooijer, T Mayer, A Hartschuh, H Ebert, T Bein
Room-temperature synthesis of lead-free copper(I)-antimony(III)-based double perovskite nanocrystals Journal Article
In: APL Materials, vol. 11, no. 4, pp. 041110, 2023.
@article{nokey,
title = {Room-temperature synthesis of lead-free copper(I)-antimony(III)-based double perovskite nanocrystals},
author = {S Wang and D Han and C Maheu and Z Xu and A Biewald and H Illner and R Hooijer and T Mayer and A Hartschuh and H Ebert and T Bein},
url = {https://aip.scitation.org/doi/abs/10.1063/5.0144708},
doi = {10.1063/5.0144708},
year = {2023},
date = {2023-04-05},
journal = {APL Materials},
volume = {11},
number = {4},
pages = {041110},
abstract = {In the field of perovskite solar cells, explorations of new lead-free all-inorganic perovskite materials are of great interest to address the instability and toxicity issues of lead-based hybrid perovskites. Recently, copper-antimony-based double perovskite materials have been reported with ideal band gaps, which possess great potential as absorbers for photovoltaic applications. Here, we synthesize Cs2CuSbCl6 double perovskite nanocrystals (DPNCs) at ambient conditions by a facile and fast synthesis method, namely, a modified ligand-assisted reprecipitation method. We choose methanol as a solvent for precursor salts as it is less toxic and easily removed in contrast to widely used dimethylformamide. Our computational structure search shows that the Cs2CuSbCl6 structure containing alternating [CuCl6]5− and [SbCl6]3− octahedral units is a metastable phase that is 30 meV/atom higher in energy compared to the ground state structure with [CuCl3]2− and [SbCl6]3− polyhedra. However, this metastable Cs2CuSbCl6 double perovskite structure can be stabilized through solution-based nanocrystal synthesis. Using an anion-exchange method, Cs2CuSbBr6 DPNCs are obtained for the first time, featuring a narrow bandgap of 0.9 eV. Finally, taking advantage of the solution processability of DPNCs, smooth and dense Cs2CuSbCl6 and Cs2CuSbBr6 DPNC films are successfully fabricated.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In the field of perovskite solar cells, explorations of new lead-free all-inorganic perovskite materials are of great interest to address the instability and toxicity issues of lead-based hybrid perovskites. Recently, copper-antimony-based double perovskite materials have been reported with ideal band gaps, which possess great potential as absorbers for photovoltaic applications. Here, we synthesize Cs2CuSbCl6 double perovskite nanocrystals (DPNCs) at ambient conditions by a facile and fast synthesis method, namely, a modified ligand-assisted reprecipitation method. We choose methanol as a solvent for precursor salts as it is less toxic and easily removed in contrast to widely used dimethylformamide. Our computational structure search shows that the Cs2CuSbCl6 structure containing alternating [CuCl6]5− and [SbCl6]3− octahedral units is a metastable phase that is 30 meV/atom higher in energy compared to the ground state structure with [CuCl3]2− and [SbCl6]3− polyhedra. However, this metastable Cs2CuSbCl6 double perovskite structure can be stabilized through solution-based nanocrystal synthesis. Using an anion-exchange method, Cs2CuSbBr6 DPNCs are obtained for the first time, featuring a narrow bandgap of 0.9 eV. Finally, taking advantage of the solution processability of DPNCs, smooth and dense Cs2CuSbCl6 and Cs2CuSbBr6 DPNC films are successfully fabricated.
7.
D Han, M-H Du, M Huang, S Wang, G Tang, T Bein, H Ebert
In: Physical Review Materials, vol. 6, no. 11, pp. 114601, 2022.
@article{nokey,
title = {Ground-state structures, electronic structure, transport properties and optical properties of Ca-based anti-Ruddlesden-Popper phase oxide perovskites},
author = {D Han and M-H Du and M Huang and S Wang and G Tang and T Bein and H Ebert},
url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.6.114601},
doi = {10.1103/PhysRevMaterials.6.114601},
year = {2022},
date = {2022-11-07},
journal = {Physical Review Materials},
volume = {6},
number = {11},
pages = {114601},
abstract = {Anti-Ruddlesden-Popper (ARP) phase oxide perovskites Ca4OA2 (A=P, As, Sb, Bi) have recently attracted great interest in the field of ferroelectrics and thermoelectrics, whereas their optoelectronic application is limited by their indirect band gaps. In this work, we introduce A-site anion ordering in Ca4OA2 (A=P, As, Sb, Bi), and find that it induces an indirect-to-direct band gap transition. Using first-principles calculations, we study the ground-state structures, electronic structure, transport properties and optical properties of anion-ordered ARP phase oxide perovskites Ca4OAA′. Based on analyses of the lattice dynamics, the ground-state structures of Ca4OAsSb and Ca4OAsBi are identified in P4/nmm symmetry and those of Ca4OPSb and Ca4OPBi are in the I222 symmetry. In contrast to the Ruddlesden-Popper (RP) phase oxide and halide counterparts, Ca4OAA′ (AA′=PSb, PBi, AsSb, AsBi) show larger band dispersion along the out-of-plane direction, smaller band gaps and highly enhanced out-of-plane mobilities, which results from the short interlayer distances and the enhanced covalency of the pnictides. Although the out-of-plane mobilities of these n=1 ARP phase perovskites highly increase, the comparatively strong polar optical phonon scattering limits the further enhancement of their mobilities. Furthermore, compared to RP phase halide Cs2PbI2Cl2, Ca4OAA′ show strong optical absorption around the band edges, and their optical absorption coefficients can reach 10^5 cm−1 within the visible light region due to small band gaps. This study reveals that these ARP phase oxide perovskites exhibit the potential for optoelectronic applications.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Anti-Ruddlesden-Popper (ARP) phase oxide perovskites Ca4OA2 (A=P, As, Sb, Bi) have recently attracted great interest in the field of ferroelectrics and thermoelectrics, whereas their optoelectronic application is limited by their indirect band gaps. In this work, we introduce A-site anion ordering in Ca4OA2 (A=P, As, Sb, Bi), and find that it induces an indirect-to-direct band gap transition. Using first-principles calculations, we study the ground-state structures, electronic structure, transport properties and optical properties of anion-ordered ARP phase oxide perovskites Ca4OAA′. Based on analyses of the lattice dynamics, the ground-state structures of Ca4OAsSb and Ca4OAsBi are identified in P4/nmm symmetry and those of Ca4OPSb and Ca4OPBi are in the I222 symmetry. In contrast to the Ruddlesden-Popper (RP) phase oxide and halide counterparts, Ca4OAA′ (AA′=PSb, PBi, AsSb, AsBi) show larger band dispersion along the out-of-plane direction, smaller band gaps and highly enhanced out-of-plane mobilities, which results from the short interlayer distances and the enhanced covalency of the pnictides. Although the out-of-plane mobilities of these n=1 ARP phase perovskites highly increase, the comparatively strong polar optical phonon scattering limits the further enhancement of their mobilities. Furthermore, compared to RP phase halide Cs2PbI2Cl2, Ca4OAA′ show strong optical absorption around the band edges, and their optical absorption coefficients can reach 10^5 cm−1 within the visible light region due to small band gaps. This study reveals that these ARP phase oxide perovskites exhibit the potential for optoelectronic applications.
6.
D Han, S S Rudel, W Schnick, H Ebert
Self-doping behavior and cation disorder in MgSnN2 Journal Article
In: Physical Review B, vol. 105, no. 12, pp. 125202, 2022.
@article{nokey,
title = {Self-doping behavior and cation disorder in MgSnN2},
author = {D Han and S S Rudel and W Schnick and H Ebert},
url = {https://link.aps.org/doi/10.1103/PhysRevB.105.125202},
doi = {10.1103/PhysRevB.105.125202},
year = {2022},
date = {2022-03-28},
urldate = {2022-03-28},
journal = {Physical Review B},
volume = {105},
number = {12},
pages = {125202},
abstract = {Investigations on II−Sn−N2(II=Mg, Ca) have been started very recently compared to the intense research of Zn−IV−N2 (IV=Si, Ge, Sn). In this work, we study the phase stability of MgSnN2 and ZnSnN2 in wurtzite and rocksalt phases by first principles calculations. The calculated phase diagram agrees with the experimental observation; i.e., MgSnN2 can form in the wurtzite and rocksalt phases while ZnSnN2 only crystallizes in the wurtzite phase. Due to the higher ionicity of Mg-N bonds compared to Sn-N bonds and Zn-N bonds, wurtzite-type
MgSnN2 appears under Mg-rich conditions. The defect properties and doping behavior of MgSnN2 in the wurtzite phase are further investigated. We find that MgSnN2 exhibits self-doped n-type conductivity, and donor-type antisite defect SnMg is the primary source of free electrons. The high possibility of forming the stoichiometry-preserving MgSn+SnMg defect complex leads to our study of cation disorder in MgSnN2 by using the cluster expansion method with first principles calculations. It is found that cation disorder in MgSnN2 induces a band-gap reduction because of a violation of the octet rule. The local disorder, namely, forming (4,0) or (0,4) tetrahedra, leads to an appreciable band-gap reduction and hinders the enhancement of the optical absorption.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Investigations on II−Sn−N2(II=Mg, Ca) have been started very recently compared to the intense research of Zn−IV−N2 (IV=Si, Ge, Sn). In this work, we study the phase stability of MgSnN2 and ZnSnN2 in wurtzite and rocksalt phases by first principles calculations. The calculated phase diagram agrees with the experimental observation; i.e., MgSnN2 can form in the wurtzite and rocksalt phases while ZnSnN2 only crystallizes in the wurtzite phase. Due to the higher ionicity of Mg-N bonds compared to Sn-N bonds and Zn-N bonds, wurtzite-type
MgSnN2 appears under Mg-rich conditions. The defect properties and doping behavior of MgSnN2 in the wurtzite phase are further investigated. We find that MgSnN2 exhibits self-doped n-type conductivity, and donor-type antisite defect SnMg is the primary source of free electrons. The high possibility of forming the stoichiometry-preserving MgSn+SnMg defect complex leads to our study of cation disorder in MgSnN2 by using the cluster expansion method with first principles calculations. It is found that cation disorder in MgSnN2 induces a band-gap reduction because of a violation of the octet rule. The local disorder, namely, forming (4,0) or (0,4) tetrahedra, leads to an appreciable band-gap reduction and hinders the enhancement of the optical absorption.
MgSnN2 appears under Mg-rich conditions. The defect properties and doping behavior of MgSnN2 in the wurtzite phase are further investigated. We find that MgSnN2 exhibits self-doped n-type conductivity, and donor-type antisite defect SnMg is the primary source of free electrons. The high possibility of forming the stoichiometry-preserving MgSn+SnMg defect complex leads to our study of cation disorder in MgSnN2 by using the cluster expansion method with first principles calculations. It is found that cation disorder in MgSnN2 induces a band-gap reduction because of a violation of the octet rule. The local disorder, namely, forming (4,0) or (0,4) tetrahedra, leads to an appreciable band-gap reduction and hinders the enhancement of the optical absorption.
5.
R Guo, D Han, W Chen, L Dai, K Ji, Q Xiong, S Li, L K Reb, M A Scheel, S Pratap, N Li, S Yin, T Xiao, S Liang, A L Oechsle, C L Weindl, M Schwartzkopf, H Ebert, P Gao, K Wang, M Yuan, N C Greenham, S D Stranks, S V Roth, R H Friend, P Müller-Buschbaum
Degradation mechanisms of perovskite solar cells under vacuum and one atmosphere of nitrogen Journal Article
In: Nature Energy, vol. 6, no. 10, pp. 977-986, 2021, ISSN: 2058-7546.
@article{nokey,
title = {Degradation mechanisms of perovskite solar cells under vacuum and one atmosphere of nitrogen},
author = {R Guo and D Han and W Chen and L Dai and K Ji and Q Xiong and S Li and L K Reb and M A Scheel and S Pratap and N Li and S Yin and T Xiao and S Liang and A L Oechsle and C L Weindl and M Schwartzkopf and H Ebert and P Gao and K Wang and M Yuan and N C Greenham and S D Stranks and S V Roth and R H Friend and P M\"{u}ller-Buschbaum},
url = {https://doi.org/10.1038/s41560-021-00912-8},
doi = {10.1038/s41560-021-00912-8},
issn = {2058-7546},
year = {2021},
date = {2021-10-01},
urldate = {2021-10-01},
journal = {Nature Energy},
volume = {6},
number = {10},
pages = {977-986},
abstract = {Extensive studies have focused on improving the operational stability of perovskite solar cells, but few have surveyed the fundamental degradation mechanisms. One aspect overlooked in earlier works is the effect of the atmosphere on device performance during operation. Here we investigate the degradation mechanisms of perovskite solar cells operated under vacuum and under a nitrogen atmosphere using synchrotron radiation-based operando grazing-incidence X-ray scattering methods. Unlike the observations described in previous reports, we find that light-induced phase segregation, lattice shrinkage and morphology deformation occur under vacuum. Under nitrogen, only lattice shrinkage appears during the operation of solar cells, resulting in better device stability. The different behaviour under nitrogen is attributed to a larger energy barrier for lattice distortion and phase segregation. Finally, we find that the migration of excessive PbI2 to the interface between the perovskite and the hole transport layer degrades the performance of devices under vacuum or under nitrogen.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Extensive studies have focused on improving the operational stability of perovskite solar cells, but few have surveyed the fundamental degradation mechanisms. One aspect overlooked in earlier works is the effect of the atmosphere on device performance during operation. Here we investigate the degradation mechanisms of perovskite solar cells operated under vacuum and under a nitrogen atmosphere using synchrotron radiation-based operando grazing-incidence X-ray scattering methods. Unlike the observations described in previous reports, we find that light-induced phase segregation, lattice shrinkage and morphology deformation occur under vacuum. Under nitrogen, only lattice shrinkage appears during the operation of solar cells, resulting in better device stability. The different behaviour under nitrogen is attributed to a larger energy barrier for lattice distortion and phase segregation. Finally, we find that the migration of excessive PbI2 to the interface between the perovskite and the hole transport layer degrades the performance of devices under vacuum or under nitrogen.
4.
D Han, C Feng, M-H Du, T Zhang, S Wang, G Tang, T Bein, H Ebert
Design of High-Performance Lead-Free Quaternary Antiperovskites for Photovoltaics via Ion Type Inversion and Anion Ordering Journal Article
In: Journal of the American Chemical Society, vol. 143, no. 31, pp. 12369-12379, 2021, ISSN: 0002-7863.
@article{,
title = {Design of High-Performance Lead-Free Quaternary Antiperovskites for Photovoltaics via Ion Type Inversion and Anion Ordering},
author = {D Han and C Feng and M-H Du and T Zhang and S Wang and G Tang and T Bein and H Ebert},
url = {https://doi.org/10.1021/jacs.1c06403},
doi = {10.1021/jacs.1c06403},
issn = {0002-7863},
year = {2021},
date = {2021-08-02},
urldate = {2021-08-02},
journal = {Journal of the American Chemical Society},
volume = {143},
number = {31},
pages = {12369-12379},
abstract = {The emergence of halide double perovskites significantly increases the compositional space for lead-free and air-stable photovoltaic absorbers compared to halide perovskites. Nevertheless, most halide double perovskites exhibit oversized band gaps (\>1.9 eV) or dipole-forbidden optical transition, which are unfavorable for efficient single-junction solar cell applications. The current device performance of halide double perovskite is still inferior to that of lead-based halide perovskites, such as CH3NH3PbI3 (MAPbI3). Here, by ion type inversion and anion ordering on perovskite lattice sites, two new classes of pnictogen-based quaternary antiperovskites with the formula of X6B2AA′ and X6BB′A2 are designed. Phase stability and tunable band gaps in these quaternary antiperovskites are demonstrated based on first-principles calculations. Further photovoltaic-functionality-directed screening of these materials leads to the discovery of 5 stable compounds (Ca6N2AsSb, Ca6N2PSb, Sr6N2AsSb, Sr6N2PSb, and Ca6NPSb2) with suitable direct band gaps, small carrier effective masses and low exciton binding energies, and dipole-allowed strong optical absorption, which are favorable properties for a photovoltaic absorber material. The calculated theoretical maximum solar cell efficiencies based on these five compounds are all larger than 29%, comparable to or even higher than that of the MAPbI3 based solar cell. Our work reveals the huge potential of quaternary antiperovskites in the optoelectronic field and provides a new strategy to design lead-free and air-stable perovskite-based photovoltaic absorber materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The emergence of halide double perovskites significantly increases the compositional space for lead-free and air-stable photovoltaic absorbers compared to halide perovskites. Nevertheless, most halide double perovskites exhibit oversized band gaps (>1.9 eV) or dipole-forbidden optical transition, which are unfavorable for efficient single-junction solar cell applications. The current device performance of halide double perovskite is still inferior to that of lead-based halide perovskites, such as CH3NH3PbI3 (MAPbI3). Here, by ion type inversion and anion ordering on perovskite lattice sites, two new classes of pnictogen-based quaternary antiperovskites with the formula of X6B2AA′ and X6BB′A2 are designed. Phase stability and tunable band gaps in these quaternary antiperovskites are demonstrated based on first-principles calculations. Further photovoltaic-functionality-directed screening of these materials leads to the discovery of 5 stable compounds (Ca6N2AsSb, Ca6N2PSb, Sr6N2AsSb, Sr6N2PSb, and Ca6NPSb2) with suitable direct band gaps, small carrier effective masses and low exciton binding energies, and dipole-allowed strong optical absorption, which are favorable properties for a photovoltaic absorber material. The calculated theoretical maximum solar cell efficiencies based on these five compounds are all larger than 29%, comparable to or even higher than that of the MAPbI3 based solar cell. Our work reveals the huge potential of quaternary antiperovskites in the optoelectronic field and provides a new strategy to design lead-free and air-stable perovskite-based photovoltaic absorber materials.
3.
M Ogura, D Han, M M Pointner, L S Junkers, S S Rudel, W Schnick, H Ebert
Electronic properties of semiconducting Zn(Si, Ge, Sn)N2 alloys Journal Article
In: Physical Review Materials, vol. 5, no. 2, pp. 024601, 2021.
@article{,
title = {Electronic properties of semiconducting Zn(Si, Ge, Sn)N2 alloys},
author = {M Ogura and D Han and M M Pointner and L S Junkers and S S Rudel and W Schnick and H Ebert},
url = {https://link.aps.org/doi/10.1103/PhysRevMaterials.5.024601},
doi = {10.1103/PhysRevMaterials.5.024601},
year = {2021},
date = {2021-02-02},
urldate = {2021-02-02},
journal = {Physical Review Materials},
volume = {5},
number = {2},
pages = {024601},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2.
D Han, H Ebert
Identification of Potential Optoelectronic Applications for Metal Thiophosphates Journal Article
In: ACS Applied Materials & Interfaces, vol. 13, no. 3, pp. 3836-3844, 2021, ISSN: 1944-8244.
@article{,
title = {Identification of Potential Optoelectronic Applications for Metal Thiophosphates},
author = {D Han and H Ebert},
url = {https://doi.org/10.1021/acsami.0c17818},
doi = {10.1021/acsami.0c17818},
issn = {1944-8244},
year = {2021},
date = {2021-01-27},
urldate = {2021-01-27},
journal = {ACS Applied Materials \& Interfaces},
volume = {13},
number = {3},
pages = {3836-3844},
abstract = {Metal thiophosphates are a large family of compounds that received far less attention than conventional chalcogenides. Recently, however, metal thiophosphates arouse research interest in regard of energy harvesting and conversion due to their structural and chemical diversity. Nevertheless, there remain many unexplored metal thiophosphates. Here, we performed a comprehensive investigation on the electronic and optoelectronic properties of a series of metal thiophosphates using first-principles calculations and identified several highly promising compounds as p-type transparent conductors, photovoltaic absorbers, and single visible-light-driven photocatalysts for water splitting. Our investigation reveals the intrinsic features of a series of typical metal thiophosphates, identifies their new optoelectronic applications, and validates that metal thiophosphates are promising materials deserving exploration.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metal thiophosphates are a large family of compounds that received far less attention than conventional chalcogenides. Recently, however, metal thiophosphates arouse research interest in regard of energy harvesting and conversion due to their structural and chemical diversity. Nevertheless, there remain many unexplored metal thiophosphates. Here, we performed a comprehensive investigation on the electronic and optoelectronic properties of a series of metal thiophosphates using first-principles calculations and identified several highly promising compounds as p-type transparent conductors, photovoltaic absorbers, and single visible-light-driven photocatalysts for water splitting. Our investigation reveals the intrinsic features of a series of typical metal thiophosphates, identifies their new optoelectronic applications, and validates that metal thiophosphates are promising materials deserving exploration.
1.
D Han, M Ogura, A Held, H Ebert
Unique Behavior of Halide Double Perovskites with Mixed Halogens Journal Article
In: ACS Applied Materials & Interfaces, vol. 12, no. 33, pp. 37100-37107, 2020, ISSN: 1944-8244.
@article{,
title = {Unique Behavior of Halide Double Perovskites with Mixed Halogens},
author = {D Han and M Ogura and A Held and H Ebert},
url = {https://doi.org/10.1021/acsami.0c08240},
doi = {10.1021/acsami.0c08240},
issn = {1944-8244},
year = {2020},
date = {2020-07-23},
urldate = {2020-07-23},
journal = {ACS Applied Materials \& Interfaces},
volume = {12},
number = {33},
pages = {37100-37107},
abstract = {Engineering halide double perovskite (A2M+M3+XVII6) by mixing elements is a viable way to tune its electronic and optical properties. In spite of many emerging experiments on halide double perovskite alloys, the basic electronic properties of the alloys have not been fully understood. In this work, we chose Cs2AgBiCl6 as an example and systematically studied electronic properties of its different site alloys Cs2NaxAg1\textendashxBiCl6, Cs2AgSbxBi1\textendashxCl6, and Cs2AgBi(BrxCl1\textendashx)6 (x = 0.25, 0.5, 0.75) by first-principles calculations. Interestingly, the halogen site alloy shows opposite behavior to M+ and M3+ cation site alloys; that is, Cs2AgBi(BrxCl1\textendashx)6 displays virtual crystal behavior without substantial broadening, while Cs2NaxAg1\textendashxBiCl6 and Cs2AgSbxBi1\textendashxCl6 show split-band behaviors with substantial broadening, which indicates that lifetimes of electrons and holes in Cs2AgBi(BrxCl1\textendashx)6 would be longer than those in Cs2NaxAg1\textendashxBiCl6 and Cs2AgSbxBi1\textendashxCl6. We further found that long lifetimes of electrons and holes are common for mixed halide perovskites. Moreover, the band alignment is provided to determine the band gap change of alloys and to understand the transport of electrons and holes when these pure compounds form heterostructures. Our systematical studies should be helpful for future optoelectronic applications of halide perovskites.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Engineering halide double perovskite (A2M+M3+XVII6) by mixing elements is a viable way to tune its electronic and optical properties. In spite of many emerging experiments on halide double perovskite alloys, the basic electronic properties of the alloys have not been fully understood. In this work, we chose Cs2AgBiCl6 as an example and systematically studied electronic properties of its different site alloys Cs2NaxAg1–xBiCl6, Cs2AgSbxBi1–xCl6, and Cs2AgBi(BrxCl1–x)6 (x = 0.25, 0.5, 0.75) by first-principles calculations. Interestingly, the halogen site alloy shows opposite behavior to M+ and M3+ cation site alloys; that is, Cs2AgBi(BrxCl1–x)6 displays virtual crystal behavior without substantial broadening, while Cs2NaxAg1–xBiCl6 and Cs2AgSbxBi1–xCl6 show split-band behaviors with substantial broadening, which indicates that lifetimes of electrons and holes in Cs2AgBi(BrxCl1–x)6 would be longer than those in Cs2NaxAg1–xBiCl6 and Cs2AgSbxBi1–xCl6. We further found that long lifetimes of electrons and holes are common for mixed halide perovskites. Moreover, the band alignment is provided to determine the band gap change of alloys and to understand the transport of electrons and holes when these pure compounds form heterostructures. Our systematical studies should be helpful for future optoelectronic applications of halide perovskites.