Dual function of formamidinium chloride additive improves the efficiency and stability of low-dimensional perovskite solar cells

Despite their excellent intrinsic stability,low-dimensional Ruddlesden-Popper(LDRP)perovskites face challenges with low power conversion efficiency(PCE),primarily due to the widen bandgap and limited charge transport caused by the bulky spacer cation.Herein,we introduce formamidinium chloride(FACl)as an additive into(4-FPEA)2MA4Pb5I16 perovskite.On the one hand,the addition of FACl narrows the bandgap through cation exchange between MA^(+)and FA^(+),thereby extending the light absorption range and enhancing photocurrent generation.On the other hand,this MA^(+)/FA^(+)cation exchange decelerates the sublimation of methylammonium chloride and prolongs the crystallization of LDRP perovskite,leading to higher crystallinity and better film quality with a decreased trap-state density.Consequently,this approach led to a remarkable PCE of 20.46%for<n>=5 LDRP perovskite solar cells(PSCs),ranking among the highest for MA/FA mixed low dimensional PSCs reported to date.Remarkably,our PSCs maintained 90%and 92%of the initial efficiency even after 1300 h at(60±5)℃and(60±5)%relative humidity,respectively.This work promotes the development of LDRP PSCs with excellent efficiency and environmental stability for potential commercial application.