2D Dion–Jacobson CsPbI₃ with Enhanced Interlayer Coupling for Stable and Efficient Photovoltaics

Inorganic 2D layered CsPbI₃ is awaiting to overcome the phase instability of traditional 3D components. However, the most reported Ruddlesden–Popper (RP) phase 2D CsPbI₃ leads to larger interlayer distance and weaker interlayer coupling since the existence of the van der Waals gap, which deteriorates the performance of the device and makes the improvement of stability unsatisfactory. Herein, this work resorts ethylenediamine cations (EDA²⁺) to construct a series of Dion–Jacobson (DJ) phase 2D CsPbI₃ as (EDA)Cs_n−1Pb_nI_3n+1 with van der Waals gap eliminated. Combining simulation calculations and experiments, it is found that the (EDA)Cs_n−1Pb_nI_3n+1 has enhanced intermolecular forces to overcome the problem of insufficient crystallization power caused by large steric hindrance in the film assembly process compared to phenethylammonium-based RP phase analogues. In addition, profit from the reduced interlayer distance and stronger coupling, the rigidity of the structure is increased, and the annoying non-radiative recombination caused by structural fluctuations is alleviated. As a result, the 2D layered DJ phase CsPbI₃-based solar cells deliver eminent performance than RP phase analogues, especially the 2D (EDA)(Cs)₄Pb₅I₁₆ (n = 5) device exhibits a record PCE of 10.43% in this work, and significantly enhanced stability.