报告人：Prof. Robert Hoye （University of Oxford）
报告题目：Ternary Chalcogenides for Photovoltaics
报告时间：8月3日上午10:30（周一）
报告地点：909-B厅
报告摘要：
Bismuth-based semiconductors have gained increasing attention as potential nontoxic alternatives to lead-halide perovskites [1]. Whilst most attention has been on bismuth-halide-based compounds, there is growing interest in broader families of materials, including chalcogenides, such as ABZ2 materials (A = monovalent cation; B = Bi3+ or Sb3+; Z = chalcogen) [2]. This talk discusses our work on two such compounds: NaBiS2 and AgBiS2.
We show NaBiS2 nanocrystals to have a steep absorption onset, with absorption coefficients reaching >105 cm-1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-timescale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS2 nanocrystals. These unusual features arise due to cation disorder, with inhomogeneous disorder leading to localised S p states forming that contribute to the formation of small hole polarons [3]. Whilst this severely reduces charge-carrier mobilities, we find that it is still possible to extract charge-carriers in photovoltaic devices, with external quantum efficiencies >50% achievable [4].
The second part of this talk focuses on AgBiS2, which is a stable near-infrared absorber, with a bandgap of 1 eV. With power conversion efficiencies exceeding 11% now, AgBiS2 is the most efficient Bi-based material used in single-junction photovoltaics. However, a limitation of this material is carrier localization, which restricts diffusion lengths to 50 nm. Whilst the strong light absorption of AgBiS2 allowed it to be used in efficient single-junction solar cells with absorber thicknesses of only 30 nm, this limits its near-infrared response. Through a combination of optical pump terahertz probe spectroscopy and first-principles calculations, we reveal that AgBiS2 does not intrinsically have carrier localization, but rather this is extrinsically induced in nanocrystals, for example through energetic disorder or high grain boundary density. We show that bulk thin films and bulk powders avoid ultrafast carrier localization, and offer pathways to thicker absorbers with stronger near-infrared response [5].
Overall, in this talk, the critical role of cation disorder in these ternary chalcogenide systems is examined, especially how they influence optical absorption and charge-carrier kinetics.
[1] Ganose, Scanlon, Walsh, Hoye,* Nat. Commun., 2022, 13, 4715.
[2] Nat. Photon., 2022, 16, 235.
[3] Huang, Kavanagh, … Hoye,* Nat. Commun., 2022, 13, 4960.
[4] Huang, … Hoye,* Adv. Funct. Mater., 2024, 2310283. DOI: 10.1002/adfm.202310283
[5] Huang, Wang, …, Hoye,* arXiv: 2602.22024 (2026)
个人简介：
Robert Hoye is an Associate Professor of Materials Chemistry at the University of Oxford, where he is also a Fellow of St. John’s College and a Royal Academy of Engineering Senior Research Fellow. Prof. Hoye completed his PhD at the University of Cambridge (2012-2014), followed by a postdoc at MIT (2015-2016), before returning to the University of Cambridge as a College Research Fellow (2016-2019). In 2020, he moved to Imperial College London as a Lecturer, then Senior Lecturer (Aug. 2022 -). In Oct. 2022, he moved to Oxford as Associate Professor. Prof. Hoye’s group focuses on developing inorganic semiconductors for energy applications, including metal-halide perovskite nanocrystals, and discovery of lead-free perovskite-inspired materials. His group’s research spans from fundamentals (including spectroscopy and computations) to materials synthesis and applications in photovoltaics, light-emitting diodes and detectors. More information: hoyegroup.web.ox.ac.uk
Prof. Hoye was awarded the 2026 EU-40 Prize from the E-MRS, and the 2024 RSC Beilby Medal and Prize from the RSC. He is CTO of NanoPrint Innovations Ltd.
联系人：汪永杰