Organometal Halide Perovskites: Sequential Vapor Deposition And Device Study Toward Highly Efficient Thin-Film Solar Cells

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Principal Investigator: Zhaoyang FanNumber: 1438681 The sun represents the most abundant potential source of pollution-free 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. The search for the best photovoltaic material is an active area of solar cell research. Recently, an exciting new class of photovoltaic materials called organo-metal perovskites has emerged. These materials are promising because they have low production cost, use elements and materials abundant in the earth's crust, and currently possess solar energy conversion efficiencies of over 15%. Perovskite based solar materials must be cast as a very thin film to be active for photovoltaics. A fundamental challenge for improving the solar energy conversion efficiency of these materials to is make crystalline thin films that are free of defects. The goal of this project is to make uniform, highly crystalline, and pin-hole free films designed to achieve efficiencies over 20% through a new chemical vapor deposition process. In this process, the chemical materials used to make the perovskites are added a chamber is a gaseous state in a prescribed sequence and then allowed to react on a surface at defined temperatures. This project will develop this process and study the material and photovoltaic properties of the perovskite thin films. With respect to educational activities, this project will train two PhD students and several undergraduate students in the fundamental aspects of solar cell material and device development, areas that are essential to the U.S. competitiveness in the renewable and clean energy economy. Outreach activities on solar and renewable energy will be also developed through the Student Chapter of Engineers for a Sustainable World at Texas Tech University, where trained students will serve as ambassadors for future K-12 outreach efforts through the institution's T-STEM Center. Technical DescriptionRecently, organo-metal perovskites have emerged as an exciting new class of earth-abundant photovoltaic materials with solar energy conversion efficiencies exceeding 15% and potential for low manufacturing cost. The goals of this project are to develop a sequential vapor deposition process for synthesis of organometal halide thin films with high crystalline quality, and then study the charge transport and recombination processes to probe for efficiency bottlenecks. The proposed vapor deposition process is based on sequential vapor phase transport deposition or sequential vacuum vapor deposition, and is designed to make uniform and crystalline thin films while maintaining the attributes of low cost thin film manufacturing scheme. Fundamental material studies, particularly the role of chlorine in the perovskite mixture, will provide knowledge basis for material and device design. Specifically, charge transport and recombination will be studied at the perovskite material level, and include micro-scale mapping characterization. Device level studies with two interface junctions will be performed to provide guidelines on material and interface structure design. Together, this integrated investigation of thin film synthesis, photovoltaic material characterization, and device performance characterization studies for highly crystalline perovskite based thin film solar cells has the potential to make fundamental advances in thin film solar cell technology.