Revealing Charge-Transfer Dynamics at Buried Charge-Selective Heterointerface in Highly Effective Perovskite Solar Cells.

The suboptimal carrier dynamics at the heterointerface between the perovskite and charge transport layer severely limit further performance enhancement of the state-of-the-art perovskite solar cells (PSCs). Herein, we completely map charge carrier extraction and recombination kinetics over a broad time range at buried electron-selective heterointerfaces via ultrafast transient technologies. It is revealed that the heterointerfaces carefully contain the electronic processes of free charge generation in perovskite within ∼2.8 ps, relaxation process of trap-state induced electron capturing less than ∼10.0 ps, electron extraction from perovskite to SnO 2 within ∼194 ps, trap-assisted recombination within ∼2047 ps, and recombination between back-injected electrons and remaining holes within ∼8.4 ns. Moreover, we further demonstrate that the inserted poly(vinyl alcohol) (PVA) thin layer can effectively enhance the electron extraction from perovskite to SnO 2 , block the undesired electron back injection, and significantly suppress the nonradiative recombination, contributing to the improved device parameters of photovoltage and fill factor. This work sheds light on charge-transfer limitations at the perovskite buried heterointerface and provides an effective guide of ideal heterointerface design for promoting charge transfer and improving PSC performance.