Effective Surface Treatment for High-Performance Inverted CsPbI₂Br Perovskite Solar Cells with Efficiency of 15.92

A simple and multifunctional surface treatment strategy is proposed to address the inferior-performance inverted CsPbI₂Br perovskite solar cells (PSCs). The induced-ions exchange can align energy levels, passivate both GBs and surface, and gift the solid protection from external erosions. The inverted CsPbI₂Br PSCs reveal a champion efficiency of 15.92% and superior stability after moisture, operational, and thermal ages. Developing high-efficiency and stable inverted CsPbI₂Br perovskite solar cells is vitally urgent for their unique advantages of removing adverse dopants and compatible process with tandem cells in comparison with the regular. However, relatively low opening circuit voltage (V_oc) and limited moisture stability have lagged their progress far from the regular. Here, we propose an effective surface treatment strategy with high-temperature FABr treatment to address these issues. The induced ions exchange can not only adjust energy level, but also gift effective passivation. Meanwhile, the gradient distribution of FA⁺ can accelerate the carriers transport to further suppress bulk recombination. Besides, the Br-rich surface and FA⁺ substitution can isolate moisture erosions. As a result, the optimized devices show champion efficiency of 15.92% with V_oc of 1.223 V. In addition, the tolerance of humidity and operation get significant promotion: maintaining 91.7% efficiency after aged at RH 20% ambient condition for 1300 h and 81.8% via maximum power point tracking at 45 °C for 500 h in N₂. Furthermore, the unpackaged devices realize the rare reported air operational stability and, respectively, remain almost efficiency (98.9%) after operated under RH 35% for 600 min and 91.2% under RH 50% for 300 min.