Development of cost-effective photovoltaic cells is one of the long-term, clean energy solutions for clean energy, air pollution, and energy security. An ideal strategy is to achieve efficient photovoltaic cells via depositing a naturally abundant active layer using a low-cost, low-temperature process. Organic perovskites are emerging as photovoltaic materials characterized by their excellent crystallinity, large optical extinction coefficient, and a suitable bandgap. In the last several years, the organic perovskite-based photovoltaic devices have experienced a faster increase in efficiency than any other solar cell technology. However, the basic understanding on the mechanisms of the photovoltaic behavior of organic perovskites is still in its infancy. This project explores the fundamental mechanisms with the ultimate goal to process organic perovskite materials with superior physicochemical properties for solar cell applications, and thus contributes to the technological development of renewable energy sources. The educational activities are well integrated with the research including: (1) promoting research training and teaching in nanoscience and clean energy technology for graduates and undergraduate students; (2) involving K-12 student and Nebraska residents through open-to-the-public events, such as 'Sunday with a Scientist' and 'Nanocamp'.
The goal of this project is to investigate, at both the macro- and nanoscopic levels, two of the most important fundamental aspects related to the physical mechanisms of photovoltaic behavior of the organolead trihalide perovskite materials: (1) the role of chlorine (Cl) concentration in enhancing the photovoltaic behavior through the increased carrier diffusion length, and (2) the origin of the switchable photovoltaic effect. This project builds upon the principal investigator's expertise on stable high-quality crystalline perovskite films and high-efficiency perovskite solar cell devices, control of preferential grain orientation by Cl incorporation, and the switchable photovoltaic effect. Scanning probe microscopy (including conducting atomic force microscopy, piezoresponse force microscopy and Kelvin probe force microscopy) and macroscopic testing techniques (such as transient photovoltage, transient photocurrent, impedance spectroscopy, steady photocurrent and dark-current measurements) are used to investigate the effect of grain size and orientation on charge generation, transport, and recombination in perovskite thin films and devices. A combination of nanoscale studies of perovskite solar cells provides information critically important for understanding the underlying physical mechanism of the photovoltaic effect and enhancement of the functionalities of the perovskite-based solar cell devices.