Achieving Small Temperature Coefficients in Carbon‐Based Perovskite Solar Cells by Enhancing Electron Extraction

Abstract Hole transport layer (HTL)‐free carbon electrode‐based perovskite solar cells (C‐PSCs) have drawn great attention due to their excellent stability and simple fabrication process. However, the photovoltaic parameters of C‐PSCs usually exhibit large negative temperature coefficients (TCs). Herein, the TCs of C‐PSCs can be suppressed by enhancing electron extraction. An efficient electron transport layer (ETL), [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)‐coated nanoneedle‐like brookite TiO₂ (ND‐B‐TiO₂) is used as ETL to prepare HTL‐free pure FAPbI₃‐based C‐PSCs. Compared with bare ND‐B‐TiO₂, PCBM@ND‐B‐TiO₂ shows higher electron mobility, and better band alignment with formamidinium lead triiodide (FAPbI₃) perovskite, as well as improved contact with perovskite, which leads to enhanced electron extraction and transportation. Consequently, the power conversion efficiency (PCE) of HTL‐free carbon‐based FAPbI₃ PSC can reach up to 14.55%, which is one of the highest efficiencies for FAPbI₃‐based planar C‐PSCs so far. More importantly, the optimized device is less sensitive to the operating temperature due to the boosted carrier extraction and passivated interface defects, showing a small TC(PCE) of only ≈−0.11%/°C between 25 °C and 85 °C. The work demonstrates that enhancing electron extraction is an effective way to achieve high‐performance C‐PSCs and high‐temperature solar cells.