Evaluating the potential of CsBiSCl2 as a solar absorber

Journal article

Efforts to develop lead-free and stable alternatives to halide perovskites have thus far mostly yielded materials with power conversion efficiencies (PCEs) well below 10% in solar cells. Recently, photovoltaics based on CsBiSCl₂ were reported to achieve 10.38% PCE. Still, the crystal structure is unknown, and it is unclear whether the reported thin film synthesis method could realize thin films with the desired phase and stoichiometry. Herein, we use ab initio Random Structure Searching (AiRSS) with a bespoke machine learned interatomic potential to explore the potential energy surface of CsBiSCl₂, finding the previously-proposed cubic perovskite structure to be implausible. The lowest-energy structure we find is a four formula unit orthorhombic structure (Pnma space group) that lies 2.4 meV per atom above the convex hull. There is strong competition in the Cs–Bi–S–Cl family, which can lead to phase impurities. By examining the reported solution synthesis method, we find that it is challenging to obtain the dimethylammonium bismuth sulfide intermediate product, and that Bi₂S₃ with dimethylammonium iodide on the surface likely forms instead. The significant I-containing residues in this intermediate results in Cs₃Bi₂I₉ being preferentially formed in thin films instead of CsBiSCl₂. Solid state synthesis without I present leads to phase impurities, consistent with the lowest-energy CsBiSCl₂ phase being metastable. Taking these experimental and computational results together, it is unlikely that >10%-efficient CsBiSCl₂ solar cells have been achieved.

Authors: Quinn, EL; Lohan, H; Tmava, E; Dong, S; Walsh, A

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Royal Society of Chemistry
• Journal: EES Solar
• Volume: 1
• Issue: 6
• Pages: 1173–1183 |
• Publication date: 2025-10-28
• Acceptance date: 2025-10-26
• DOI: 10.1039/d5el00157a
• EISSN: 3033-4063
• Language: English