Structural Analysis and Carrier Relaxation Dynamics of 2D CsPbBr<sub>3</sub> Nanoplatelets
Kritiman Marjit, Goutam Ghosh, Srijon Ghosh, S. Sain, Arnab Ghosh, Amitava Patra
Abstract
Two-dimensional (2D) cesium lead halide perovskite nanoplatelets (NPLs) have received tremendous attention due to their unique properties for designing solar cell applications. Here, we investigated the crystal structure of 2D CsPbBr3 nanoplatelets (NPLs) and their ultrafast carrier relaxation dynamics with varying the monolayer (ML) thickness using femtosecond transient absorption spectroscopy (fs-TAS). Rietveld analysis suggested that the basal planes of the NPLs are composed of (101) and (101) planes while the remaining four facets (thickness) are composed of (101), (101), (010), and (010) planes of the orthorhombic phase. The formation of the orthorhombic CsPbBr3 NPLs by stacking the structural motifs of PbBr6 octahedra in the crystallographic directions is evident from the atomic modeling. The change of monolayer thickness leads to a red-shift of the excitonic absorption band and PL band and enhancement of decay time. The cooling dynamics of the hot carrier to the band-edge state by phonon emission varies from 140 to 210 fs with thickness by modification of quantum confinement and dielectric screening. We observed both energy and charge transfer between 2D CsPbBr3 NPLs with an organic chromophore, N,N′-bis(hexadecyl)perylene-3,4,9,10-tetracarboxylic acid diimide (PDI), which is thickness-dependent. A deep understanding of the photoinduced carrier dynamics of the 2D CsPbBr3 NPLs will pave the way to designing 2D perovskite-based photovoltaic devices.