Abstract
Zero-dimensional (0D) inorganic perovskites have attracted great interest for white-light-emitting applications because of their broad band emissions originating from self-trapped excitons. In this work, we explore and decipher exciton self-trapping in a series of 0D inorganic perovskites, A(4)PbX(6) and A(4)SnX(6) (A = K, Rb, and Cs; X = Cl, Br, and I) at the density functional theory level within the theoretical framework of the one-dimensional configuration coordinate diagram. We demonstrate that the formation of self-trapped states in A(4)PbX(6) and A(4)SnX(6) can be attributed to local structural distortions of individual [PbX6](4-) and [SnX6](4-) octahedra. Importantly, with the goal of both potentially improving the stability of the Sn derivatives and enhancing the emission efficiency, we further propose and design two types of 0D perovskite heterostructures, bulk A(4)PbX(6)/A(4)SnX(6) mixtures and A(4)PbX(6)/A(4)SnX(6) heterojunctions. We find that these 0D heterostructures exhibit type-I energy level alignment in which energy transfer from A(4)PbX(6) to A(4)SnX(6) is strongly promoted. Interestingly, these heterostructures show an increase in the transition dipole moments between the ground and self-trapped states compared to the pristine 0D perovskites. Our findings provide a new material design strategy for boosting self-trapped emissions with improved air stability for white-light-emitting applications.