Pushing the Limit of Open‐Circuit Voltage Deficit via Modifying Buried Interface in CsPbI 3 Perovskite Solar Cells

Abstract Although CsPbI 3 perovskites have shown tremendous potential in the photovoltaic field owing to their excellent thermal stability, the device performance is seriously restricted by severe photovoltage loss. The buried titanium oxide/perovskite interface plays a critical role in interfacial charge transport and perovskite crystallization, which is closely related to open‐circuit voltage deficit stemming from nonradiative recombination. Herein, target molecules named 3‐sulphonatopropyl acrylate potassium salts are deliberately employed with special functional groups for modifying the buried interface, giving rise to favorable functions in terms of passivating interfacial defects, optimizing energetic alignment, and facilitating perovskite crystallization. Experimental characterizations and theoretical calculations reveal that the buried interface modification inhibits the electron transfer barrier and simultaneously improves perovskite crystal quality, thereby reducing trap‐assisted charge recombination and interfacial energetic loss. Consequently, the omnibearing modification regarding the buried interface endows the devices with an impressive efficiency of 20.98%, achieving a record‐low V OC deficit of 0.451 V. The as‐proposed buried interface modification strategy renders with a universal prescription to push the limit of V OC deficit, showing a promising future in developing high‐performance all‐inorganic perovskite photovoltaics.