Over 8% efficient CsSnI3-based mesoporous perovskite solar cells enabled by two-step thermal annealing and surface cationic coordination dual treatment

Abstract

All-inorganic tin halide perovskite compounds, such as CsSnI₃, have attracted attention in the field of solar cells due to their eco-friendly properties. It is quite a challenge to fabricate high-quality CsSnI₃ perovskite films with low defect density due to the low defect tolerance and overquick crystallization growth rate. Herein, we propose a simple yet effective method to modulate the dynamic balance between the growth and nucleation of perovskite crystals for black orthorhombic phase CsSnI₃. We found that well-crystallized CsSnI₃ thin films can be easily obtained through two-step thermal annealing at low temperatures of 40 °C and 70 °C. We further introduced 1-(4-carboxyphenyl)-2-thiourea to coordinate with surface undercoordinated Sn²⁺ cations of CsSnI₃ thin films through CS and CO functional groups, significantly decreasing the defect density. The CsSnI₃ perovskite solar cells based on a printable c-TiO₂/m-TiO₂/Al₂O₃/NiO/carbon mesoporous framework achieved a power conversion efficiency of 8.03% with high reproducibility, which is the best efficiency among those reported for all-inorganic CsSnI₃ mesoporous perovskite solar cells to date. Furthermore, the corresponding devices retained 90% of the initial efficiency after 3000 hours of storage in a N₂-filled glovebox.