A Compact and Smooth CH3NH3PbI3 Film: Investigation of Solvent Sorts and Concentrations of CH3NH3I towards Highly Efficient Perovskite Solar Cells

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 (MAPbI(3)) film. It was found that the morphology of the perovskite MAPbI(3) 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 MAPbI(3) 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).