Electrical Performance Measurements of Photovoltaics and Wide Band Gap Semiconductors for Power Electronics

In FY 20, our new hyperspectral imaging system was used extensively for the first time to measure PV luminescence data on (mostly) multijunction solar cells in electroluminescence mode. The results of these early measurements were encouraging, and we performed baseline calibration measurements to obtain absolute electroluminescence data. In FYs 21 through 24, we focused on performing extensive electroluminescence and photoluminescence measurements using the hyperspectral imager on a variety of PV materials including GaAs and CdTe PV films or devices. With the delivery of a new optical cryostat in FY 21, we have been able to carry out these measurements as a function of temperature down to 77 K using liquid nitrogen. Measurements at such low temperatures have revealed novel, previously unexplored phenomena in some devices that could be important for understanding reliability issues for these materials in cold conditions such as deployment in space satellites. We intend to continue these temperature-dependent measurements into FY26 with new perovskite solar cells provided to us by two important collaborators, the University of Toledo and the Korea Research Institute of Chemical Technology. These new measurements will increase our scientific understanding of defects and shunts in these materials and will shed light on charge carrier transport phenomena in these devices.

Another research topic where electroluminescence imaging is important for understanding of defects, local damage, and failure modes in materials is tied to a study started in FY 25 on field-aged and/or damaged photovoltaic modules. We obtained several 10-year-old, hail-damaged PV modules from a local field to build a database of the electroluminescence imaging and full electrical characterization of these modules. In FY26, we intend to continue to build this database and work on modeling and image analysis techniques to develop a quantitative picture of degradation and failure modes with these and other aged modules. The goal of this study is to inform life cycle analysis models as it relates to longevity and reliability of these products in the market. 

In FY24 and 25, we designed and built an apparatus for testing and characterization of power semiconductor transistors and diodes using a pulsed, high-power current-voltage setup. We also designed and built an inverter power module for testing of DC power to AC power conversion. Our plan in FY26 is to further automate our measurement setup and build additional monitoring and data acquisition channels. Also, we will build new circuitry for reliability testing of individual transistors under pulsed operating conditions and characterize failure modes. The goal of this work is to obtain a better understanding of failure mechanisms inside these devices by collaborating with other NIST researchers and explore whether we can correlate electrical characterization with materials characterization and modeling.