Micro-scale Light Emission and Morphological Properties of Mixed Halide Perovskites

Mixed halide perovskites are a solar cell material candidate consisting of two cations and halide ions, generally a mix of Iodide (I) and Bromide (Br), that can be used to improve the efficiencies of single-junction or tandem solar cells. We have analyzed halide segregation in perovskites, where halides that are generally homogeneously distributed separate into inhomogeneous regions under light, which decreases the effectiveness of solar cells. Most research on halide segregation in perovskites has averaged over large regions, but we have done micro-scale individual grain analysis. We use a confocal microscope to map the photoluminescence excited by a 488nm laser on specific areas of perovskite samples and a scanning electron microscope to get clear morphological images of the grains. Our research categorizes different types of grains that exhibit distinct segregation dynamics, which is vital to understanding how halide segregation occurs. We also found that using perovskites with 5% chlorine (Cl), in addition to I and Br, reduces halide segregation. This will help create more energy-efficient solar panels, enabling the world to transition to more effective green energy sources.