In this study, lead-free perovskite CsSn(IxBr1−x)3 films with photoluminescence emission wavelengths from 677 to 887 nm are prepared. The influence of air exposure on their characteristics is also investigated. It is found that CsSnI3 can be transformed to Cs2SnI6 upon increasing the air exposure time. The decomposition and oxidation mechanisms are confirmed by the X-ray diffraction pattern due to the presence of CsI peak. It is observed that devices based on the CsSn(IxBr1−x)3 film with increased Br− ratio and the CsSnI3 film with prolonged air exposure time show inferior performance. These results are mainly attributed to the highest occupied molecular orbital levels of CsSn(IxBr1−x)3 and Cs2SnI6. Defect density of state and binding energy of these materials are also investigated and reported in this study.
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