**Pratt New Faculty Lecture Series Co-host** Solution Processing of Thin-Film Solar Cells: Opportunities and Challenges

Given the expected world population increase to above the 8 billion level by mid-century and associated ever-increasing energy demand, as well as the requirement to reduce undesirable side effects of burning fossil fuels, there is an acute need for cleaner and more sustainable forms of energy conversion. While the solution to this problem will likely involve a broad portfolio of energy options, the progressive reduction of cost and ubiquitous supply for photovoltaic (PV) technologies suggests that this pathway is poised to play a vital role in this mix. This talk will address several particularly promising thin-film PV technologies based on Cu-In-Ga-S-Se (CIGS) and Cu-Zn-Sn-S-Se (CZTS) compounds as the absorber material and a relatively simple liquid-based film deposition process that enables the fabrication of high-performance absorber layers, with resulting device sunlight-to-electricity power conversion efficiencies of as high as 15%. Key aspects of this story include focus on developing appropriate solution chemistries, and thin film deposition and defect engineering approaches. For the relatively new CZTS system, the combination of progressively higher record efficiency, earth abundant metal starting materials, and lower-cost solution-based processing opens opportunities for development of a potentially pervasive PV technology. These and other related solution-processed PV technologies, such as the recently demonstrated high-performance perovskite-based devices, provide clear indication of how solution-processing may, not only provide an avenue for low cost PV fabrication, but also for performance levels that can rival and sometimes even beat analogous vacuum-deposited devices. David Mitzi received a B.S.E. in Electrical Engineering from Princeton University in 1985 and a Ph.D. in Applied Physics from Stanford University in 1990. In 1990, he joined the IBM  T. J. Watson Research Center and initiated a program examining structure-property relationships, low-cost thin-film deposition techniques and device applications for a variety of electronic materials (e.g., oxides, halides, chalcogenides, organic-inorganic hybrids). Between 2009 and 2014 he managed the Photovoltaic Science and Technology group at IBM, with a focus on developing solution-processed high-performance inorganic semiconductors for thin-film PV devices, before moving to the Department of Mechanical Engineering and Materials Science at Duke University in July 2014.   He holds a number of patents and has authored or coauthored more than 170 papers and book chapters.