The remarkable performance of organometallic halide perovskites in photovoltaic and light-emitting applications has stimulated extensive studies to understand underlying fundamental photophysics. However, the spatial heterogeneity arising from the presence of crystalline grains with distinct size, shape, and level of defects in solution-processed thin films imposes significant challenges for experimental studies. An understanding of the electronic excited-state processes, their spatial dependencies and underlying physical mechanisms requires experimental approaches with not only spatial and temporal resolution but also with a capability for simultaneously accessing morphological information for the same region of interest. Here, we will report our recent studies on solution-processed thin films of pristine and mixed halide perovskites (CH3NH3PbI3 and CH3NH3PbI3-xClx) based on multimodal all-optical imaging measurements. Specifically, steady-state photoluminescence (PL) and femtosecond transient absorption microscopies (TAM) were applied to probe spatially dependent electronic dynamics, whereas confocal reflectance and transmission imaging microscopies were used to gain morphological information at the same spatial locations. The combination of these non-destructive imaging modalities on a single optical microscope platform with comparable spatial resolution enables us to reveal several salient spatial features. We observed distinct spatial features in all images, which appear particularly rich in both PL and confocal reflectance images. A strong correlation between the PL and confocal reflectance images is further identified. In contrast, neither correlation nor anti-correlation can be found in all other combinations of these acquired images. The mechanisms underlying these findings and their implications for accessing spatially resolved properties in other systems will be also discussed.

Accessing spatial heterogeneity in halide lead perovskite thin films with multimodal optical imaging

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.