Synergistic Interface Modification and Crystal Growth Regulation via a Fluorinated Sulfonate Multifunctional Buried Additive for High‐Efficiency CsPbI3 Perovskite Solar Cells Exceeding 21%

Interfacial defects at the perovskite/ETL interface and poor crystallization processes limit CsPbI₃ perovskite solar cells' performance. A pentafluoroaniline trifluoromethane sulfonate (PFAT)-PbI₂ hybrid solution is deposited on the surface of TiO₂ ETL. This modification effectively passivates defects in both the TiO₂ and perovskite layers, while enhancing CsPbI₃ crystallinity. The optimized device achieves a power conversion efficiency (PCE) of 21.36%.

Abstract

All inorganic CsPbI₃ perovskites have attracted significant attention due to their excellent thermal stability and ideal bandgap characteristics. However, interfacial defects at the perovskite/electron transport layer (ETL) interface and uncontrolled crystallization processes of the perovskite remain critical bottlenecks for advancing device performance. Herein, a multifunctional buried interface-modifying additive, pentafluoroaniline trifluoromethane sulfonate (PFAT), is employed. Analytical results confirm that PFAT can effectively anchor at the TiO₂/perovskite interface while passivating defects in both layers, thereby suppressing interfacial recombination losses. Furthermore, this modification can reduce the surface energy of the CsPbI₃ crystal plane, promoting perovskite crystallization and yielding films with enhanced crystallinity. To strengthen PFAT-perovskite interactions, a PFAT-PbI₂ hybrid solution (PFATLI) is synthesized for interfacial modification. Consequently, the optimized PFATLI-modified device achieved a power conversion efficiency (PCE) of 21.36%, an open-circuit voltage (V _OC) of 1.23 V, and a fill factor (FF) of 83.44%. For the larger-area devices with an active area of 1 cm², the PCE reached 17.41%, while under the weak illumination conditions, the PCE further increased to 41.27%. After 800 h of storage in an ambient environment with 5% relative humidity (RH) at room temperature (RT), the unencapsulated device retained 87.27% of its initial efficiency.