A-site cation engineering enables oriented Ruddlesden-Popper perovskites towards efficient solar cells

Quasi two-dimensional（Q-2D） perovskites with favorable environment stability and satisfied device performance are attracting great attention and becoming star materials.The unique characteristics of more wide range of Goldschmidt tolerance factor endow Q-2D perovskites with exceptional composition tunability and great potential.Herein,Guanidinium（Gua） was firstly introduced into the octahedral cation site of BA2MA3Pb4I13 perovskite to partially replace methylammonium（MA）.With the incorporation of Gua,the XRD intensity ratio of（202）/（111） increased nearly 100% for control and 0.10Gua-mixed Q-2D perovskite,from1.49 to 2.84,indicating that the layered perovskite crystallization orientation is significantly regulated.Coupling with GIWAXS results,a preferential orientation Q-2D perovskite film was obtained.Meanwhile,the Gua-based Q-2D perovskite exhibits significantly reduced nonradiative recombination,which greatly promotes the efficient transport of carriers leading to a high efficiency of 15.41% in the BA2(MA0.9GA0.1)3Pb4I13-based solar cell.Moreover,the solar cells display superior environmental stability at an average humidity of 35%±5% in the air for 1200 h.This work points the way to the regulation of crystal orientation for enhancing the performance of Q-2D perovskite by the A-site cation engineering.