Building-up process of power conversion in carbon-electrode-based, hole-conductor-free mesoscopic perovskite solar cells

The building-up process of power conversion in carbon-electrode-based mesoscopic perovskite solar cells is monitored by prolonging the annealing period of the lead halide perovskite (PVSK) precursor in the mesoporous skeleton in open air. It is observed that power conversion occurs only after 20 min of annealing, though severe hysteresis is seen due to the existence of an intermediate phase. Meanwhile, the heterojunction structure evolves obviously in the device, from that formed between the electron transport layer (ETL) and PVSK precursor, to that formed between ETL and PVSK crystallites. As annealing time increases to 120 min, the intermediate phase is reduced, and the buried interface of PVSK is strengthened, leading to accelerated charge-extraction and retarded charge-recombination, as well as an upgraded built-in potential (Vbi). Accordingly, the power conversion efficiency (PCE) improves from 10.47% to 12.42%, with the hysteresis index sharply dropping from 19.19% to 1.06%. Increasing the carbon-electrode thickness and prolonging the annealing time could further improve the crystallization quality of PVSK, thus elevating the PCE up to 15.26%, as well as the T80 lifetime of ∼390 h for unsealed devices, during the quasi-maximum power point tracking test in open air.