Transient response of cadmium telluride modules to light exposure

Commercial cadmium telluride (CdTe) photovoltaic (PV) modules from three different manufacturers were monitored for performance changes during indoor and outdoor light-exposure. Short-term transients in V_oc were recorded on some modules, with characteristic times of ~1.1 hours. Outdoor performance data shows a similar drop in V_oc after early morning light exposure. Preliminary analysis of FF changes show light-induced changes on multiple time scales, including a long time scale. Multiple methods of measuring βV_oc resulted in a range of values on the same CdTe PV module between -0.25%/C and -0.4%/C, possibly due to concurrent light-induced V_oc transients and temperature changes. This paper highlights the need for rapid performance measurement of PV samples following light exposure and the possibility of incorrect results when using outdoor light exposure to collect values of βV_oc for CdTe modules.