Enhanced Solvent Strategy for High-Quality Perovskite Solar Cells Using Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] as a Hole Transport Layer

Triple-cation perovskite solar cells (PSCs) have attracted widespread interest for their high-power conversion efficiencies (PCEs). Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) is commonly used as a hole transport material in inverted PSCs due to its excellent charge transport properties. However, the hydrophobicity of PTAA significantly affects device performance: excessively hydrophobic surfaces hinder interfacial contact, while insufficient hydrophobicity reduces perovskite grain size and film quality. Here, we report a simple method to optimize PTAA hydrophobicity by using tetrahydrofuran (THF) as a solvent instead of conventional toluene. This adjustment promotes larger grain growth by increasing nucleation spacing and effectively passivates interface defects. As a result, the PCE improves from 17.17 to 20.89%. Furthermore, THF is a more environmentally friendly and less toxic solvent, making it a promising alternative for scalable PSC fabrication.