COLLABORATIVE RESEARCH: Understanding and harnessing structural defects, doping, passivation, and alloying to increase Voc and efficiency of CdTe solar cells

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Title: Advancing photovoltaic technologies through innovative process designNon-Technical Description:This project aims at developing new knowledge in the areas of materials science and device engineering to further advance the performance of the low cost photovoltaic (PV) technology based on CdTe. Despite the tremendous market growth and price reduction demonstrated by PV technologies over the last two decades, PV-generated electricity remains below 1% of our total electricity usage; further cost reduction could be achieved through higher device performance leading to accelerated deployment of PV. The project will investigate several processing routes to improve the output voltage of the CdTe cell, which is the remaining challenge to achieving near ideal performance. This research seek to minimize the negative impact of grain boundaries and other structural defects, in order to improve key material properties which control the output voltage of CdTe cells. The focus will be on studying elemental impurities, specifically phosphorous (P) doping, and its interaction with grain boundaries and other 2D structural defects in CdTe films and their alloys. Graduate students at both institutions will gain experience in thin film device fabrication, crystal growth, and advanced methods of characterization of materials and devices. This project will also impact students from K-12 and provide educational resources on thin film solar cells and materials on PV education. The PIs and associate graduate students will continue hands-on solar cell teaching outreach to middle and high school students. Technical Description:The main goal of this project is to create the fundamental knowledge and process techniques required to advance the output voltage of CdTe PV. This research has the following objectives: (1) investigate the effect of isolated grain boundaries in large mm grain size materials, and use the findings to tailor the properties of polycrystalline thin films; (2) investigate the combined effect of group V dopant(s) with post-deposition processing techniques on the net p-type doping; (3) enhance p-type doping by suppressing structural defects through alloying CdTe(Se,S); (4) lower interface recombination at critical device interfaces, such as the main junction and back contact, through alloying. The above goals will be pursued through a holistic approach that will include the investigation of large mm grain size bulk materials, device quality polycrystalline thin films, and state-of-the-art device structures. The experimental component of the project will be rooted in fundamental material studies and expanded to device engineering. The activities will be guided using device physics models to predict solar cell performance. Results from this project may have a direct impact on solar cell manufacturing and could lead to a paradigm shift impact in terms of improving efficiency and decreasing cost of polycrystalline CdTe-based solar cells.