Elucidating the Factors Limiting the Photovoltaic Performance of Mixed Sb–Bi Halide Elpasolite Absorbers

Although Cs2AgBiBr6 halide elpasolites have gained substantial attention as potential nontoxic and stable alternatives to lead–halide perovskites, they are limited by their wide bandgaps >2.2 eV. Alloying with Sb into the pnictogen site has been shown be an effective method lower bandgap, but this not translated improvements in photovoltaic (PV) performance. Herein, underlying causes investigated. Pinhole-free films of Cs2Ag(SbxBi1−x)Br6 achieved through antisolvent dripping, PV devices still exhibit a reduction power conversion efficiency from 0.44% ± 0.02% (without Sb) 0.073% 0.007% (90% Sb; lowest bandgap). There is 0.7 V open-circuit voltage, which correlates appearance sub-bandgap state ≈0.7 eV below optical bandgap Sb-containing elpasolite films, found both absorbance photoluminescence measurements. Through detailed Williamson–Hall analysis, it that adding leads increase film strain. This strain relieved aerosol-assisted solvent treatment, reduces density energetic disorder well reducing fast early decay photogenerated carrier population due trap filling. work shows alloying introduction extra states limit performance, can mitigated post-annealing treatment reduce