Synergistic effect through the introduction of inorganic zinc halide in the interface of TiO2 and Sb2S3 for high-performance Sb2S3 planar thin film solar cell

The competition between charge recombination and extraction principally affects the fill factor (FF) and power conversion efficiency (PCE) of planar thin-film solar cells. In Sb2S3 thin-film solar cells, the electrocharge recombination and extraction n transport layer (ETL) plays a significant role in electron extraction and determination of Sb2S3 film absorber quality. Herein, a TiO2 ETL is strategically modified using an inorganic salt zinc halide (i.e., ZnCl2, ZnBr2, ZnI2), which simultaneously improves the electronic properties of TiO2 and promotes the growth of Sb2S3 films with larger grain size and higher crystallinity. The experimental results and theoretical calculations further reveal that the zinc halide can interact with TiO2 and simultaneously bond strongly with the upper Sb2S3 film, which creates a unique pathway for electron transfer, passivates the trap states, and alleviates the recombination losses effectively. As a result, an average PCE of 6.87 ± 0.11% and the highest PCE of 7.08% have been attained with an improved FF from 51.22 to 61.61% after ZnCl2 introduction. Additionally, introduction of ZnCl2 helps the unencapsulated devices to maintain 93% of their original performance after 2400 h of storage in a nitrogen-filled glovebox. This work develops an effective route for the optimization of ETLs and defect healing using simple and low-cost inorganic salts.