[NH3(CH2)6NH3]PbI4 as Dion-Jacobson Phase Bifunctional Capping Layer for 2D/3D Perovskite Solar Cells with High Efficiency and Excellent UV Stability

Currently, three-dimensional (3D) organic–inorganic hybrid metallic halide perovskites are emerging as optoelectronic materials, but they demonstrate poor stability against heat and moisture and are vulnerable to oxidation and photodegradation upon exposure to ultraviolet (UV) light. Herein, for the first time, 1,6-diaminohexane ammonium (HDAD+) is demonstrated to be a unique cation spacer to prepare a two-dimensional Dion-Jacobson phase (DJP) perovskite that is ultimately used to construct a 2D/3D stacking structure. Compared to 3D perovskites and Ruddlesden-Popper phase (RPP)-2D perovskites, the DJP-2D perovskite demonstrates superior UV stability and can efficiently protect the 3D layer underneath from being damaged by the UV light. Moreover, the DJP-2D perovskite can also act as an interfacial layer to passivate the defects located on top of the 3D perovskite, resulting in a notably increased photoluminescence lifetime and suppression of interfacial charge recombination. As a result, the power conversion efficiency (PCE) is enhanced from 19.22% (3D) to 20.31% (2D/3D) and is accompanied by improved moisture and thermal stabilities.