Dangling Octahedra Enable Edge States in 2D Lead Halide Perovskites
Résumé
The structural reconstruction at the crystal layer edges of 2D lead halide perovskites (LHPs) leads to unique edge states (ES) which are manifested by prolonged carrier lifetime and reduced emission energy. These special ES could effectively enhance the optoelectronic performance of devices, but their intrinsic origin and working mechanism remain elusive. Here we demonstrate that the ES of a family of 2D Ruddlesden-Popper LHPs [BA2CsPb2Br7, BA2MAPb2Br7 and BA2MA2Pb3Br10 (BA = butylammonium; MA = methylammonium)] arise from the rotational symmetry elevation of the PbBr6 octahedra dangling at the crystal layer edges. These dangling octahedra give rise to localized electronic states that enable an effective transport of electrons from the interior to layer edges, and the population of electrons in both the intrinsic states and ES can be manipulated via controlling the external fields. Moreover, the abundant phonons, activated by the dangling octahedra, can interact with electrons to facilitate radiative recombination, counterintuitive to the suppressive role commonly observed in conventional semiconductors. This work unveils the intrinsic atomistic and electronic origins of ES in 2D LHPs, which could stimulate the exploration of ES-based exotic optoelectronic properties and corresponding design of high-performance devices for these emergent low-dimensional semiconductors.