Microscale Thermal Inhomogeneity Enabled Bandgap Engineering in Perovskite Nanowire Arrays

Thermal transport at the microscopic level is intuitively considered as a fast and random process. However, here the formation of significant microscale thermal inhomogeneity in single nanowires (NWs) of halide perovskites is reported, where the temperature gradient can be further converted to a compositional gradient via bandgap engineering. Upon employing a heat source or heat sink in the setup, arrays of composition‐graded NWs are fabricated by anion‐exchange with halogen‐containing vapor. Quantitative analysis from multiple spatial‐resolved scanning probe characterizations suggests that the exchange reaction occurs globally with a monotonically decreased rate along individual NWs, and the corresponding thermal simulation reveals a prominent temperature gradient up to 3.6 °C µm −1 in the axial direction. The large thermal inhomogeneity is attributed to the ultra‐low thermal conductivity of perovskites combined with reduced nanowire (NW) diameter. In addition, the gradient NWs exhibit excellent optoelectronic features suitable for further integration into functional devices. This work provides guidelines for the composition manipulation of perovskites through phononic engineering, extending their applications in ultracompact microspectrometers, spectral imaging sensors, and other miniaturized optoelectronic devices.