Temperature-dependent light-stabilized states in thin-film PV modules

Thin-film photovoltaic modules are known to exhibit light-induced transient behavior which interferes with accurate and repeatable measurements of power. Typically power measurements are made after a light exposure in order to target a “light state” of the module that is representative of outdoor performance. Here we show that the concept of a unique light state is poorly defined for both CIGS and CdTe modules. Instead we find that their metastable state after a light exposure can depend on the temperature of the module during the exposure. We observe changes in power as large as 5.8% for a 20°C difference in light exposure temperature. These results lead us to conclude that for applications in which reproducibility and repeatability are critical, module temperature should be tightly controlled during light exposure.