UC Davis

As global energy demands escalate, the need for technological advancements in alternative energy sources becomes crucial to counter climate change. Hybrid organic-inorganic perovskites (HOIPs) have demonstrated great promise for optoelectronics, owing to their tunable bandgap, cost-effectiveness, and simplicity in fabrication. Despite their rapidly growing efficiency and popularity among the scientific community, they suffer from sensitivity to exposure to different environmental stressors (humidity, temperature, oxygen, light, and bias). To quantify the effects of similar surface treatments on perovskites, nanoscale spatial resolution with scanning probe microscopy (SPM) methods are required. Leveraging the ability to resolve electrical characteristics of grains and grain boundaries with Kelvin probe force microscopy (KPFM), we investigate HOIP material systems, exploring the ion migration and charge trapping in grain boundaries in response to varying humidity conditions, and the effect of treatment with additives on humidity stability. Our results elucidate the transience of surface voltage distribution at various humidity exposure durations, due to a complex interaction between the mobile ions and water and the role of grain boundaries in this process. We see improvement in surface voltage and better resistance to humidity with additive treatment. Understanding the exact mechanism of interaction of water with photovoltaic materials is essential to harness the full potential of these materials for their application in commercial solar technologies. Overall, we anticipate the environmental, in situ and ex situ microscopy developed in this thesis to be extended for interrogating other halide perovskite families, including Pb-free options.