Aveena Abee Varghese, Junyi Gong, Nirmal Prashanth Maria Joseph Raj, Graham A. Turnbull, Lethy Krishnan Jagadamma
2D Ruddlesden–Popper (RP) perovskites are a promising candidate for photovoltaics and indoor light harvesting. In this study we investigate the low‐dimensional RP perovskite [CH 3 (CH 2 ) 3 NH 3 ] 2 (CH 3 NH 3 ) 3 Pb 4 I 13 ( n = 4) for indoor photovoltaics, and optimize the phase distribution by the method of substrate preheating. Enhancements in the photovoltaic device performance from thickness optimization and processing conditions yield quasi‐2D halide perovskites with champion power conversion efficiency of 23.1% (RV) under indoor lighting conditions.