Polymer Additives for Morphology Control in High‐Performance Lead‐Reduced Perovskite Solar Cells

The organic–inorganic halide perovskite solar cells (PSCs) are rapidly developed in just a few years due to its high power conversion efficiency. However, it still faces some critical issues, one of which is the presence of toxic lead (Pb2+). Recent researches show that barium (Ba2+) can partially replace the Pb2+ in perovskite structure and achieve a promising device performance because of its adequate ionic radius. However, the optimal replacement amount of Ba2+ in perovskite is still limited. Herein, the methylammonium (MA)/formamidinium (FA) mixed‐cation perovskite is used as the active layer in PSCs and Pb2+ is partially substituted with Ba2+. Compared with the pure MA system, the best device efficiency can be achieved using higher Ba2+ replacement ratio. In addition, while introducing the appropriate polymer additive, the replacement ratio can be further increased without compromise of device efficiency. Using polyethylene glycol as polymer additive, 10.0 mol% Ba‐doped MA/FA mixed‐cation PSC with an efficiency of 16.1% can be realized. It is believed that this report provides an effective strategy to fabricate high‐performance lead‐reduced PSCs.