Buried interface treatment using alkali metal hydroxides for efficient and durable perovskite solar cells

The buried interface in perovskite solar cells (PSCs) is pivotal in influencing the quality of the perovskite films and the efficiency of charge extraction and transport. Recent studies have highlighted the potential of alkali metal ion-based materials for modifying this interface. In this work, we present the first systematic investigation of the effects of different alkali metal hydroxide treatments at the buried interface between the SnO₂ electron transport layer and the perovskite light absorber layer. Our findings demonstrate that KOH treatment significantly enhances the power conversion efficiency (PCE), while CsOH treatment improves operational durability. To achieve a balance between efficiency and durability, we developed a dual alkali metal hydroxide treatment strategy. Notably, the sequence of hydroxide deposition was found to be critical. A KOH treatment followed by CsOH increased the efficiency of mixed cation-based PSCs from 18.46% to 20.31% and improved durability, allowing the device to retain 95% of its initial efficiency after 500 h of continuous illumination at room temperature. Furthermore, this dual treatment enhanced the PCE of formamidinium lead iodide-based PSCs from 21.31% to 21.68%, along with improved operational stability. This study introduces a straightforward yet highly effective method for buried interface modification, offering a versatile approach to simultaneously boost efficiency and durability in a wide range of PSC architectures.