Transient Absorption Microscopy Study of Excited-State Dynamics and the Structural Origins in Metal Halide Perovskites [thesis]

Xinyi Jiang
2021 unpublished
Metal halide perovskites have recently emerged as one of the most promising active layers in solar cells for their high power conversion efficiency (>25%) and ease of synthesis and deposition. Spatial heterogeneity is inevitable with current fabrication methods for both monocrystalline and polycrystalline perovskite thin films and crystals. The morphologydependent imaging of the excited-state dynamics is crucial to the understanding of the conversion efficiency resulting from different
more » ... on methods. Key processes affecting the performance of the absorber layers include carrier recombination, carrier cooling, and carrier trapping, which mostly happen on the ultrafast timescale (sub-picosecond). To capture all the processes happening across a broad energy landscape, broadband detection is required. In this work, broadband pump-probe spectroscopy and confocal microscopy are combined into one setup, the transient absorption microscope (TAM), to realize hyperspectral imaging of the ultrafast dynamics in metal halide perovskites. Studies on both perovskite thin films and crystals were performed. The first part of the thesis is focused on mapping the morphology-related carrier dynamics in polycrystalline perovskite thin films. Fundamental carrier properties like the Fermi energy level, cooling rate, and defect concentration were extracted from the transient absorption (TA) spectrum acquired at every single pixel. Hundreds of pixels were scanned in one experiment, and the correlations between the carrier properties and the morphological information, for example, grain boundary (GB), were verified using statistical models. The high-dimensional datasets containing spatial, spectral, temporal, and morphological information create the challenge of analyzing gigabytes of correlated data, which typically takes enormous computational resources. To solve this problem,
doi:10.21985/n2-5da8-f705 fatcat:x4o4qnuvfndh7ofhqjijyun3p4