Synergistic optimization of minimal antisolvent processing and dopant-free HTMs for high-efficiency perovskite solar cells†

Conventionally, 300 μL or more of anti-solvent is used for perovskite film formation in spin-coating processes. In this study, the amount of anti-solvent is reduced successfully to 8 μL, less than 3% of the conventional anti-solvent amount (300 μL). This result is produced by combining the displacement of dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidone (NMP) and the presence of moisture during fabrication. Furthermore, dopant-free HTMs are newly synthesized based on monovalent cations on carbazoles. Different from our previous dopant-free HTM where the triphenylamine moiety was positioned at the 3,6-positions of the carbazole core, the newly designed CIM+ HTMs adopt a structural isomer with triphenylamine units directly connected to the 2,7-positions of the carbazole backbone. This positional rearrangement resulted in a deeper HOMO energy level and significantly enhanced current characteristics compared to the previous structure. The combination of the small anti-solvent procedure with novel dopant-free HTMs facilitates PSCs achieving a power conversion efficiency exceeding 21%. This result demonstrates the superior photoelectric properties of the method, attributable to enhanced reproducibility and electrical stability.