Alkyl ammonium salt with different chain length for high-efficiency and good-stability 2D/3D hybrid perovskite solar cells

Recently, 2D/3D halide perovskites solar cells (PSCs) attract extensive attention due to simultaneous improved efficiency and stability. However, the types of alkyl ammonium salts, including the type of functional groups, the number of carbon atoms in the hydrocarbon chain, as well as the arrangement and distribution of the molecular structure, have a great impact on the performance and stability of films and devices. Herein, we compare the passivation capacity and moisture resistance of 2D capping layer based on three structurally similar alkyl ammonium salts (Butyl Ammonium Iodide (BAI), Propyl Ammonium Iodide (PAI), Ethyl Ammonium Iodide (EAI)) on triple cation perovskite thin films. As the number of carbon atoms in the alkane increases, the water contact angle gradually increases. Moreover, the defect state density is reduced to a certain extent compared to untreated 3D perovskite. The optimal PSCs with PAI-based 2D capping layer exhibit a power conversion efficiency (PCE) of 21.22% and remain 79.5% of initial PCE after 720 h. In addition, the reduced defect state density and improved crystallinity can be attributed to the hydrogen bonding interaction between the amine group and the [PbI6](4-)framework. The emergence and development of 2D/3D perovskites have brought greater hope to commercialize the PSCs.