Four solvents (isopropanol (IPA), n-butyl alcohol (NBA), n-amyl alcohol (NAA), and n-hexyl alcohol (NHA)) were investigated to prepare CH₃NH₃I (methylammonium iodide, MAI) solutions to transform PbI₂ film into CH₃NH₃PbI₃ (MAPbI₃) film. It was found that the morphology of the perovskite MAPbI₃ film was not only affected by the chain of the solvent molecule, but also by the concentration of MAI. The use of solvents with a long alkyl chain (NAA and NHA) allowed the MAPbI₃ to grow via an in situ transformation step, which easily made the perovskite films compact, but with a high surface roughness due to the growth of unexpected nanorods/nanoplates. The solvent with a short alkyl chain (IPA) led to the dissolution-crystallization growth mechanism, resulting in rapid generation of perovskite films with a number of pinholes. A high-quality (compact, smooth, pinhole-free) perovskite film was obtained with NBA and an optimized MAI concentration of 8 mg/mL. The corresponding perovskite solar cells achieved a maximum power conversion efficiency (PCE) of 16.66% and average PCE of 14.76% (for 40 cells).
Keywords: compact; perovskite solar cells; smooth; solvent.