Enhanced charge transport in A-site ordered perovskite derivatives A2A'Bi2I9 (A = Cs; A' = Ag, Cu): a first-principles study

Shuhan Li; Siyu Song; Peng Lv; Shihao Wang; Jiawang Hong; Gang Tang

doi:10.1039/d5cp00956a

Enhanced charge transport in A-site ordered perovskite derivatives A₂A'Bi₂I₉ (A = Cs; A' = Ag, Cu): a first-principles study

Phys Chem Chem Phys. 2025 Jul 1. doi: 10.1039/d5cp00956a. Online ahead of print.

Authors

Shuhan Li^{1

2}, Siyu Song^{1

2}, Peng Lv³, Shihao Wang^{1

2}, Jiawang Hong⁴, Gang Tang^{1

2}

Affiliations

¹ School of Interdisciplinary Science, Beijing Institute of Technology, Beijing 100081, China. gtang@bit.edu.cn.
² Beijing Institute of Technology, Zhuhai Beijing Institute of Technology (BIT), Zhuhai 519088, P. R. China.
³ Henan Key Laboratory of High Efficiency Energy Conversion Science and Technology, Henan International Joint Laboratory of New Energy Materials and Devices, School of Physics and Electronics, Henan University, Kaifeng 475004, China. lvpeng@henu.edu.cn.
⁴ School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, China.

PMID: 40590146
DOI: 10.1039/d5cp00956a

Abstract

Recent experiments have synthesized Cs₂AgBi₂I₉ by partially substituting Cs⁺ with Ag⁺ at the A-site of Cs₃Bi₂I₉, resulting in enhanced charge transport properties compared to Cs₃Bi₂I₉. However, the atomic-scale mechanisms behind this enhancement remain unclear. In this work, we investigate the carrier transport mechanisms in Cs₂A'Bi₂I₉ (A' = Ag, Cu) using first-principles calculations and Boltzmann transport equation. Our results reveal that A-site ordered Cs₂A'Bi₂I₉ exhibits carrier mobilities that are 3-4 times higher than those of Cs₃Bi₂I₉ within the 100-500 K temperature range. We identify polar phonon scattering as the dominant mechanism limiting mobility. Furthermore, the enhanced out-of-plane carrier mobility in Cs₂A'Bi₂I₉, particularly between 100 and 200 K, leads to reduced mobility anisotropy. These improvements are mainly due to the shorter A'-I bond lengths and increased Ag⁺/Cu⁺ s-I^- p orbital coupling. Notably, substitution with Cu⁺ results in a further reduction in the band gap and enhanced hole mobility compared to Ag⁺ substitution in Cs₃Bi₂I₉. Further analysis reveals that the significant increase in carrier mobility in Cs₂A'Bi₂I₉ can be largely explained by the smaller carrier effective masses (m*) and weaker Fröhlich coupling strengths (α), resulting in a lower polar mass α(m*/m_e), compared to Cs₃Bi₂I₉. Our study provides valuable insights into the transport properties of Bi-based perovskite derivatives, paving the way for their future applications in optoelectronic devices.