Solvent annealing is an efficient method to fabricate high quality perovskite film with less grain boundaries. While most works carried out focused on the solvent annealing of perovskite films, we annealed PbI₂ films in DMF, DMSO, acetone, and isopropanol (IPA) atmospheres and studied the effect of different atmospheres. We found that dense PbI₂ was formed by annealing in DMF, acetone, and IPA atmospheres, which impeded the full reaction between PbI₂ and CH₃NH₃I. Meanwhile, DMSO solvent annealing process led to porous PbI₂ films, which facilitated the complete conversion of PbI₂ to perovskite with larger grain sizes. As a result, Solar cells based on DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%.

We also annealed PbI₂ in DMSO and CH₃NH₃PbI₃ in ethanol for fabrication of pinhole-free CH₃NH₃PbI₃ films on ZnO nanorods. Due to the suppression of carrier recombination by large grains, ZnO nanorods based PSCs with best efficiency of 17.3% was obtained.

To suppress the interface defect, Li-doping compact TiO₂ was also used as electron transport layer (ETL). Li doping reduced electron trap density and increased the conductivity of the ETL. As a result, the Li-doped compact TiO₂ based planar heterojunction PSCs exhibit negligible hysteretic J-V behavior. Comparing with the undoped compact TiO₂ based PSCs, the PCE of the Li-doped compact TiO₂ film based PSCs is improved from 14.2% to 17.1%.