In Situ Cesium Modification at Interface Enhances the Stability of Perovskite Solar Cells

A consensus has been reached that organic transport layer (e.g., Spiro-OMeTAD) in perovskite solar cell (PSC) is prone to be impact by mobile ions in perovskite film during long-term operation. Here, we incorporate cesium acetate as a buffer layer into perovskite solar cells to mitigate this detrimental behavior, in which cesium acetate is sandwiched between perovskite and organic transport layer. The mobile ions that migrate toward the organic transport layer (e.g., MA⁺) are gradually consumed by cesium acetate, resulting in cesium-rich perovskite at the interface. This in situ reaction and the subsequent Cs incorporation greatly enhance the operational stability of PSC without efficiency loss. The optimized PSC presents a power conversion efficiency of 20.9% with an open-circuit voltage of 1.18 V, maintaining ∼80% of its initial efficiency after 4500 min continuous operation at maximum power point. This new strategy opens up a new opportunity for fabricating stable perovskite solar cells.