Effect of Sunlight Intensity on Functional Inhomogeneity and Stability of Organic-Inorganic Perovskite Solar Cells

The sun represents the most abundant potential source of sustainable energy on earth. Solar cells for producing electricity require materials that absorb the sun's energy and convert its photons to electrons, a process called photovoltaics. Recently, materials based on inorganic-organic halide perovskite materials have achieved promising solar energy power conversion efficiency approaching that of silicon solar cells, and can be made from earth-abundant elements using lower-cost, solution based fabrication methods. However, present organic-inorganic perovskite photovoltaic devices chemically degrade during long-term service under both high sunlight and moisture in air. Furthermore, present methods for their fabrication result in the inconsistent performance of the final device. The goal of this project is to develop new fabrication methods to improve the environmental stability and performance reproducibility of perovskite-based photovoltaic devices to help enable their future practical use. A unique aspect of this project is that the research will be carried out as part of a formal international collaboration between the Massachusetts Institute of Technology in the United States and the Ben-Gurion University of the Negev in Israel. Both institutions bring unique and complimentary research expertise as well as opportunities for student training.

The research plan will seek to improve environmental stability and fabrication reproducibility of perovskite-based photovoltaic devices through four material fabrication strategies: 1) introduce molecular species with specialized functionality into the active layer, 2) adjust film formation kinetics, 3) tune the chemical composition of photoactive films, and 4) add passivating agents that reduce charge trap densities. These strategies will be investigated within the context of three research objectives. The first objective is to develop a fundamental understanding the origin of the grain-to grain variability in electronic properties of methylammonium lead triiodide. The second objective is to elucidate the origin of non-radiative decay in the microscale emission. As part of this objective, the crystallographic structure and composition will be correlated to characteristic luminescence emission and electronic properties at the microscale. The third objective is to determine the factors limiting the reproducibility and environmental stability of methylammonium lead triiodide, with particular focus on identifying the mechanisms responsible for photovoltaic deterioration that limits operational device stability under concentrated sunlight.