Nanoscale Electronic Properties of Triplet-State-Engineered Halide Perovskites

Halide perovskites are currently intensively being investigated for applications in light-emitting diodes for next-generation lighting and display technology. A recent report shows that the control of triplet states is key to efficient light emission in layered quasi-2D perovskite devices. Unlike perovskite solar cells, the effect of spatial variations in the optoelectronic properties of perovskite light-emitting diodes on the overall device performance has scarcely been investigated. Here, we investigate the nanoscale electronic effects of triplet-state management in such materials using scanning probe microscopy under light illumination, in particular, Kelvin probe force microscopy, to study surface potential changes under light illumination. The recently found improvement in the efficiency of light emission can be seen in correlated contact potential differences at grains and grain boundaries under illumination. We also show that surface potential relaxation times after lighting changes depend on the dimensionality of the perovskite material and hole transfer from the perovskite inorganic lattice to the triplet energy level of the 2D spacer layer. Our findings shed new light on the design of halide perovskite-based LEDs and functional materials for improved performance.