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.