Refining the Buried Interface via Alkali Metal Carbonate for Efficient All-Inorganic Perovskite Solar Cells

The buried interface plays a critical role in determining both the efficiency and stability of perovskite solar cells (PSCs). However, defect states and energy level misalignment at the SnO2/perovskite interface can lead to significant charge recombination, severely limiting device performance. Herein, multifunctional interface modifiers based on alkali metal carbonates are introduced for carbon-based CsPbBr3 PSCs. The CO32- anions not only passivate oxygen vacancy (OV) defects and undercoordinated Sn4+ ions on the SnO2 surface to enhance electron transfer but also passivate undercoordinated Pb2+ ions at the perovskite interface, improving the overall quality of the perovskite film. Additionally, the alkali cations were found to diffuse into the perovskite bulk, enhancing crystal quality and suppressing nonradiative recombination. By leveraging this multifaceted interface engineering approach, a champion CsPbBr3 PSC achieved an impressive PCE of 10.70%. Importantly, the unencapsulated devices maintain 85% of initial efficiency under high humidity (85% RH) and heat (85 °C) over 50 days.