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%.