  Under continuous light illumination, it is known that localized domains with
segregated halide compositions form in semiconducting mixed-halide perovskites,
thus severely limiting their optoelectronic applications due to the negative
changes in bandgap energies and charge-carrier characteristics. Here we deposit
mixed-halide perovskite CsPbBr1.2I1.8 nanocrystals onto an indium tin oxide
substrate, whose temperature can be rapidly changed by ~10 degree in a few
seconds by applying or removing an external voltage. Such a sudden temperature
change induces a temporary transition of CsPbBr1.2I1.8 nanocrystals from the
segregated phase to the mixed phase, the latter of which can be permanently
maintained when the light illumination is coupled with periodic heating cycles.
These findings mark the emergence of a practical solution to the detrimental
phase-segregation problem, given that a small temperature modulation is readily
available in various fundamental studies and practical devices using
mixed-halide perovskites.
