Intermediate phase-assisted growth of CsPbBr3 for high performance of carbon-based perovskite solar cells

CsPbBr3 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 (PbBr2) to CsPbBr3 perovskite and low solubility of perovskite in organic solvent impede the further improvement of device performance in terms of CsPbBr3 solar cells. Herein, an intermediate phase-assisted growth of CsPbBr3 perovskite was proposed by introducing tetraphenylphosphonium bromide (TPPB) as additive. The TPPB is expected to react with PbBr2 in organic solvent to form an intermediate phase of [TPPB<middle dot>DMF]<middle dot>PbBr2, which not only effectively improves the crystallinity of PbBr2 crystals, but also greatly reduces the phase transition energy barrier, leading to uniform and compact CsPbBr3 perovskite films with large grain size and high crystallinity. In combination with carbon electrode, the CsPbBr3 solar cells yield a champion device performance of 9.57% in comparison of pristine CsPbBr3 solar cells showing a low efficiency of 8.17%. Furthermore, the intermediate phase-assisted growth of CsPbBr3-based solar cells displays an outstanding storage over 720 h.