Solvent annealing of PbI2 for the high-quality crystallization of perovskite films for solar cells with efficiencies exceeding 18%

Abstract

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI₂. PbI₂ films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI₂ in the DMF, acetone, and IPA atmospheres resulted in dense PbI₂ films, which impeded the complete conversion of PbI₂ to CH₃NH₃PbI₃. Surprisingly, employing the DMSO solvent annealing process for PbI₂ led to porous PbI₂, which facilitated the complete conversion of PbI₂ to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.