Morphology-Dependent Carrier Accumulation Dynamics in Mixed Halide Perovskite Thin Films Caused by Phase Segregation

The phase segregation in mixed halide perovskites is recently found to improve the photoluminescence quantum yield (PLQY) of the perovskites by concentrating the carriers. However, how phase segregation affects the photoinduced carrier dynamics is unclear. Herein, we find that the phase segregation in CH3NH3PbBrxI3-x mixed halide perovskite thin film is morphology-dependent by showing I-rich domains mainly along the grain boundaries. Ultrafast transient absorption (TA) and photoluminescence upconversion (PL-UC) spectroscopy measurements uncover that the carrier accumulation in the low energy I-rich domains includes two carrier transfer pathways. Carrier transfer from the Br-rich domain and the mixed phase to the I-rich domain is realized by consecutive hole (similar to 0.5 ps) and electron (<12.4 ps) transfer and energy transfer (<12.4 ps), respectively. The finding reveals the carrier funneling dynamic mechanism in phase-segregated halide perovskite films and provides a guideline for the applications of mixed halide perovskites in color-conversion devices or high -efficiency LEDs.

Automated summary

The phase segregation in mixed halide perovskites improves the photoluminescence quantum yield by concentrating the carriers, but its effect on the photoinduced carrier dynamics is unclear. This study demonstrates that phase segregation in CH3NH3PbBrxI3-x perovskite thin film is morphology-dependent, with I-rich domains mainly along the grain boundaries. The carrier transfer from the Br-rich domain and the mixed phase to the I-rich domain occurs through consecutive hole and electron transfer, as well as energy transfer. This finding reveals the carrier funneling dynamic mechanism in phase-segregated halide perovskite films and provides guidance for their applications in color-conversion devices or high-efficiency LEDs.