Measurement precautions for high-resistivity silicon solar cells

Several measurement characteristics have been identified that are unique to high-performance, high-resistivity silicon cells. These unique characteristics, which are due to features such as bulk carrier lifetimes on the order of 1 ms, excellent surface passivation, and light trapping, can lead to large performance measurement errors; however, they also offer insight into the physical mechanisms occurring in these devices. The characteristics that were found to have the largest influence on measured performance are described. These include a strong fill factor dependence on voltage sweep rate and direction, sublinear short-circuit current versus irradiance, light-soaking influence on open-circuit voltage and fill factor, and enhanced spectral response beyond 1100 nm due to optical light trapping. Cell measurements and analyses have included both small-area concentrator cells and large-area one-sun cells from various sources.