Improved performance and thermal stability of perovskite solar cells prepared via a modified sequential deposition process

In conventional sequential deposition, PbI2-free CH3NH3PbI3 perovskite films can be achieved when the PbI2 substrate reacts with a relatively low-concentration CH3NH3I solution (<8 mg of CH3NH3I per 1 mL of IPA) but the film that is formed has only sparse and uneven coverage. On the other hand, a dense CH3NH3PbI3 perovskite film can be formed on a mesoporous TiO2 substrate when the PbI2 substrate reacts with a relatively high-concentration MAI solution (>8 mg of CH3NH3I per 1 mL of IPA), but unreacted PbI2 is still present in CH3NH3PbI3 layer in such cases. Here, we developed organic-inorganic perovskite solar cells with high efficiency by preparing dense and PbI2-free films using a modified sequential deposition process. By utilizing the reaction behavior between PbI2 and MAI, solar cells with an average power-conversion efficiency of 15.1% and high reproducibility and stability were achieved.