Improved Efficiency of Carbon‐Based Perovskite Solar Cells by Using Alternative Solvent for Doping‐Free P3HT

Low‐temperature‐processed carbon‐based perovskite solar cells (C‐PSCs) are a potential candidate for industrial development, due to their low cost, high stability, and easy preparation methods. However, their power conversion efficiencies still lag behind that of metal‐contact‐based PSCs, due to poor compatibility of the carbon electrode with the underlying layers. Here, we introduce a doping‐free poly(3‐hexylthiophene) (P3HT) hole‐transport layer deposited from chloroform to improve solar cell performance of PSCs that are prepared in ambient air. The resulting P3HT films have a lower roughness and a higher conductivity. A champion device with power conversion efficiency of 19.4% was obtained with negligible hysteresis and a remarkably enhanced fill factor (FF) of 80.2%. Unencapsulated devices maintained 70% of initial efficiency value after 350 hr under thermal stress at 85°C in dark and ambient air.