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 CO₃^2– anions not only passivate oxygen vacancy (O_V) 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.