High-Performance 2D Dion-Jacobson Tin Perovskite Solar Cells with Improved Charge Separation and Extraction.

2D Dion-Jacobson (DJ) tin halide perovskites have been recognized as promising photovoltaic materials due to their structural stability and designable multifunctional spacer cations. However, insulating organic spacer cations will bring a dielectric confinement effect and quantum well structure. Usually, these 2D perovskites exhibit poor charge transport performance, which hinders the preparation of high-efficiency solar cells. Here, compared with p-phenylenediammonium, a multiple-ring aromatic amine 1,5-naphthalenediammonium (15-NDA) spacer is introduced. Theoretical simulation and experimental characterization demonstrate that 15-NDA with extended π-conjugation length has greater steric hindrance and can inhibit the formation of small n-phase. It can weaken the dielectric confinement effect and quantum well confinement, thus improving the exciton dissociation. Additionally, the strong π-π conjugation of 15-NDA can enhance the intermolecular interaction and help to prepare more uniform and dense films. Furthermore, the oxidation of Sn and I and the corresponding defect state density can be effectively reduced. As a result, the corresponding devices show improved carrier diffusion length and fast carrier extraction. Therefore, the 2D DJ (15-NDA)FASnI solar cells achieve a record performance of 7.33% and demonstrate improved humidity and nitrogen stability. This work provides a new approach to optimize the device performance by structural design of the organic spacers.