Bifunctional Compound Induced Dual Back Surface Fields for Efficient Hole Transport Layer‐Free Perovskite Solar Cells

extracts electrons from carbon and lowers its work function, which succeeds realizing dual BSFs. This improves the separation and extraction of photocarriers within the device, which is evidenced by the photoluminescence lifetime imaging of the device cross-section for the first time. As a result, the average open-circuit voltage increases significantly by about 70 mV, which largely contributes to the improvement of PCE with a champion value of 20.79% obtained.