Mechanistic study on the growth of Sn-doped polyaniline synthesized by one-step electropolymerization

The effect of SnCl₂ dopant concentration on the properties of Sn-doped polyaniline (PANI) as a hole transport layer (HTL) for perovskite solar cells (PSC) was investigated. PANI films were synthesized by potentiostatic electropolymerization at 1 V vs. Ag/AgCl in sulfuric acid containing 0.1 M of aniline. The study analyzed various processes, including anodic charge transfer, diffusion, crosslinking, and coordination of SnCl₂. Results showed that SnCl₂ doping decreased the branching of PANI chains and enhanced the thermal properties of PANI. The Raman spectrum confirmed crosslinking behavior due to the incorporation of Sn. Thermogravimetric analysis, derivative thermogravimetry, and differential scanning calorimetry supported SnCl₂ coordination to the PANI backbone. Optical measurements revealed a decrease in transmittance and reflectance and a substantial decrease in the band gap as the concentration of SnCl₂ increased. Mechanism of PANI growth and different early stage reactions are thoroughly discussed.