Solvent Selection for Deposition of Benzodithiophene‐Based Hole Transport Layer Determines Perovskite Solar Cell Efficiency

The structure of hole‐transport material (HTM) determines the efficiency of perovskite solar cells (PSCs). In this work, we investigate how the nature of the solvent used for the HTM deposition defines its morphology and crystallinity in thin films and the performance of PSCs. A benzodithiophene‐based material (BDT) capable of forming highly crystalline thin films was deposited from various solvents and their mixtures. Thin BDT thin films were characterized using X‐ray diffraction, optical microscopy and atomic force microscopy. BDT films deposited from heptane formed long narrow crystals and possessed large surface roughness, which significantly reduced the devices efficiency. The amorphous BDT films obtained from chlorobenzene enabled the highest efficiencies up to 16.3% in undoped PSCs.