Performance Limitations in Wide Bandgap CIGS-Based Solar Cells

University of Minnesota Ph.D. dissertation. June 2017. Major: Electrical Engineering. Advisor: Stephen Campbell. 1 computer file (PDF); viii, 142 pages.Copper Indium Gallium Selenide (CIGS) material based thin film solar devices have gathered attention in the recent years due to their high device efficiency and low cost of manufacturing making them suitable for terrestrial applications. The CIGS absorber material has an extremely high absorption coefficient with a bandgap that can be tuned from 1 -1.7eV by varying the material composition to maximize device efficiency. Research to date has shown that the highest efficiency CIGS devices are based on band gaps in the 1.1 - 1.3eV range. However, it is desirable to develop wider bandgap absorbers with bandgaps greater than 1.5eV to mitigate power loss at high operation temperatures and integration into multi-junction solar devices. As the band gap is increased greater than 1.4eV, the short circuit current falls off and the open circuit voltage (VOC) saturates. This presents a major challenge in developing high efficiency wide gap solar devices. In this work, the electronic properties of polycrystalline CIGS films with varying band gaps and material composition are studied to better understand the limitations on device performance. Electrical characterization and device modeling is used to investigate the nature of the electronic defects, and the effects on overall device performance