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

Recent experiments have synthesized CsAgBiI by partially substituting Cs with Ag at the A-site of CsBiI, resulting in enhanced charge transport properties compared to CsBiI. However, the atomic-scale mechanisms behind this enhancement remain unclear. In this work, we investigate the carrier transport mechanisms in CsA'BiI (A' = Ag, Cu) using first-principles calculations and Boltzmann transport equation. Our results reveal that A-site ordered CsA'BiI exhibits carrier mobilities that are 3-4 times higher than those of CsBiI 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 CsA'BiI, 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 CsBiI. Further analysis reveals that the significant increase in carrier mobility in CsA'BiI can be largely explained by the smaller carrier effective masses () and weaker Fröhlich coupling strengths (), resulting in a lower polar mass (/), compared to CsBiI. Our study provides valuable insights into the transport properties of Bi-based perovskite derivatives, paving the way for their future applications in optoelectronic devices.