Intermediate phase‐assisted growth of CsPbBr 3 for high performance of carbon‐based perovskite solar cells

Abstract CsPbBr 3 inorganic perovskites have been regarded as the promising materials in the field of photovoltaics because of the high tolerance against environment. The high energy barrier of phase transition from lead bromide (PbBr 2 ) to CsPbBr 3 perovskite and low solubility of perovskite in organic solvent impede the further improvement of device performance in terms of CsPbBr 3 solar cells. Herein, an intermediate phase‐assisted growth of CsPbBr 3 perovskite was proposed by introducing tetraphenylphosphonium bromide (TPPB) as additive. The TPPB is expected to react with PbBr 2 in organic solvent to form an intermediate phase of [TPPB·DMF]·PbBr 2 , which not only effectively improves the crystallinity of PbBr 2 crystals, but also greatly reduces the phase transition energy barrier, leading to uniform and compact CsPbBr 3 perovskite films with large grain size and high crystallinity. In combination with carbon electrode, the CsPbBr 3 solar cells yield a champion device performance of 9.57% in comparison of pristine CsPbBr 3 solar cells showing a low efficiency of 8.17%. Furthermore, the intermediate phase‐assisted growth of CsPbBr 3 ‐based solar cells displays an outstanding storage over 720 h.