Pb alloying enables efficient broadband emission of two dimensional [NH3(CH2)4NH3]CdBr4

Abstract Two dimensional (2D) hybrid metal halide perovskites (MHPs) with broadband emission have attracted enormous attention, which is highly promising for single-component solid state lighting. However, it remains a challenge to unveil the underlying origin of broadband emission and achieve high quantum yield (QY). Herein, 2D single-layered [NH3(CH2)4NH3]CdBr4 (Cd–P) has been successfully prepared. By partially replacing Cd2+ with Pb2+, the energy band of Cd–P shows a transformation from indirect to direct, supported by the density functional theory (DFT) calculations. Benefiting from the change of energy band, alloyed CdxPb1-x-P shows an intensive broadband emission spanning the whole visible range with a maximum of photoluminescence (PL) QY of 58%. Temperature-dependent and time-resolved PL uncover that the broadband emission origins from the coupling between free excitons (FEs) and [CdBr6]4- octahedra, instead of [PbBr6]4-. These findings provide a deep insight into the origin of STEs emission and an effective approach to promote the broadband emission for Cd-based MHPs.