Target Therapy for Buried Interface Enables Stable Perovskite Solar Cells with 25.05% Efficiency

Abstract The buried interface in perovskite solar cells (PSCs) is pivotal for achieving high efficiency and stability. However, it is challenging to study and optimize the buried interface due to its non‐exposed feature. Here, a facile and effective strategy is developed to modify the SnO 2 /perovskite buried interface by passivating the buried defects in perovskite and modulating carrier dynamics via incorporating formamidine oxalate (FOA) in SnO 2 nanoparticles. Both formamidinium and oxalate ions show a longitudinal gradient distribution in the SnO 2 layer, mainly accumulating at the SnO 2 /perovskite buried interface, which enables high‐quality upper perovskite films, minimized defects, superior interface contacts, and matched energy levels between perovskite and SnO 2 . Significantly, FOA can simultaneously reduce the oxygen vacancies and tin interstitial defects on the SnO 2 surface and the FA + /Pb 2+ associated defects at the perovskite buried interface. Consequently, the FOA treatment significantly improves the efficiency of the PSCs from 22.40% to 25.05% and their storage‐ and photo‐stability. This method provides an effective target therapy of buried interface in PSCs to achieve very high efficiency and stability.