Abstract
The physical origin of sub-band gap photoluminescence in Ruddlesden–Poppers two-dimensional (2D) lead halide perovskites (LHPs) is still under debate. In this paper, we studied the photoluminescence features from two different facets of 2D LHP single crystals: the in-plane facet (IF) containing the 2D inorganic layers and the facet perpendicular to the 2D layers (PF). At the IF, the free carriers (FCs) dominate due to the weak electron–phonon coupling in a symmetric lattice. At the PF, the strain accumulation along the 2D layers enhances the electron–phonon coupling and facilitates self-trapped exciton (STE) formation. The time-resolved PL studies indicate that free carriers (FCs) at the IF can move freely and display the trapping by the intrinsic defects. The STEs at the PF are not likely trapped by the defects due to the reduced mobility. However, with increasing STE density, the STE transport is promoted, enabling the trapping of STE by the intrinsic defects.
Highlights
The physical origin of sub-band gap photoluminescence in Ruddlesden− Poppers two-dimensional (2D) lead halide perovskites (LHPs) is still under debate
Identifying the photogenerated species and clarifying the corresponding dynamics within various local structures is essential to characterize the actual photophysics in 2D perovskite materials
We investigate the emissive state dynamics to identify the photogenerated species at two different surface facets of 2D RP lead bromide perovskite corresponding to inplane facets (IFs) and perpendicular facets (PFs) to the 2D inorganic lattice layers, respectively
Summary
The physical origin of sub-band gap photoluminescence in Ruddlesden− Poppers two-dimensional (2D) lead halide perovskites (LHPs) is still under debate.
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