Abstract
Semiconductor mixed-halide perovskites featured with a tunable energy bandgap are ideal candidates for light absorbers in tandem solar cells as well as fluorescent materials in light-emitting diodes and nanoscale lasers. These device advancements are currently hindered by the light-induced phase segregation effect, whereby ion migration would yield smaller-bandgap domains with red-shifted photoluminescence. Here we show that upon laser excitation all-inorganic mixed-halide nanocrystals unexpectedly exhibit a blue shift in the photoluminescence peak that can revert back in the dark, thus depicting the processes of ion migration out of and back to the originally excited nanocrystals. Interestingly, this reversible photoluminescence shift can also be induced by electrical biasing of mixed-halide nanocrystals without the injection of charge carriers. The above findings suggest that it is the local electric field that breaks the ionic bonds in mixed-halide nanocrystals, which could be a universal origin for light-induced phase segregation observed in other mixed-halide perovskite materials.
Highlights
Semiconductor mixed-halide perovskites featured with a tunable energy bandgap are ideal candidates for light absorbers in tandem solar cells as well as fluorescent materials in lightemitting diodes and nanoscale lasers
While the enlarged energy bandgap is mainly caused by bromine enrichment in mixed-halide CsPbBr1.2I1.8 NCs, we show that lattice distortion by the migration of iodide ions could make a minor contribution, as verified by the observation of a blue shift in the PL peak as large as 20 nm from the single-halide CsPbI3 NCs upon laser excitation
One drop of the concentrated or diluted solution of the CsPbBr1.2I1.8 NCs was spin-coated onto a fused silica substrate for the room-temperature optical characterizations of an ensemble film or single particles with a 405 nm picosecond laser operated at a repetition rate of 5 MHz
Summary
Semiconductor mixed-halide perovskites featured with a tunable energy bandgap are ideal candidates for light absorbers in tandem solar cells as well as fluorescent materials in lightemitting diodes and nanoscale lasers. These device advancements are currently hindered by the light-induced phase segregation effect, whereby ion migration would yield smaller-bandgap domains with red-shifted photoluminescence. We show that upon laser excitation allinorganic mixed-halide nanocrystals unexpectedly exhibit a blue shift in the photoluminescence peak that can revert back in the dark, depicting the processes of ion migration out of and back to the originally excited nanocrystals. For an isolated single CsPbBr1.2I1.8 NC, the PL is shifted to the blue side upon laser excitation but never returns back in the dark, signifying the necessary existence of nearby NCs to channel the migration of iodide ions
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