Constructing an Interfacial Gradient Heterostructure Enables Efficient CsPbI₃ Perovskite Solar Cells and Printed...

Severe nonradiative recombination originating from interfacial defects together with the pervasive energy level mismatch at the interface remarkably limits the performance of CsPbI₃ perovskite solar cells (PSCs). These issues need to be addressed urgently for high-performance cells and their applications. Herein, an interfacial gradient heterostructure based on low-temperature post-treatment of quaternary bromide salts for efficient CsPbI₃ PSCs with an impressive efficiency of 21.31% and an extraordinary fill factor of 0.854 is demonstrated. Further investigation reveals that Br^- ions diffuse into the perovskite films to heal undercoordinated Pb²⁺ and inhibit Pb cluster formation, thus suppressing nonradiative recombination in CsPbI₃ . Meanwhile, a more compatible interfacial energy level alignment resulting from Br^- gradient distribution and organic cations surface termination is also achieved, hence promoting charge separation and collection. Consequently, the printed small-size cell with an efficiency of 20.28% and 12 cm² printed CsPbI₃ minimodules with a record efficiency of 16.60% are also demonstrated. Moreover, the unencapsulated CsPbI₃ films and devices exhibit superior stability.