Intrinsic stability of thin-film CdS/CdTe modules

Stability of thin-film CdTe module is crucial to the advancement of the technology. Long-term stability studies are carried out under a variety of accelerated test conditions. Accelerated-life-tests (ALT) are performed in the laboratory to accelerate degradation and hence quantify performance change in reasonably short periods of time. ALT studies attempt to simulate the conditions a solar module experiences outdoors during its lifetime, and ALT results are correlated to outdoor test results to estimate module service lifetimes, nameplate parameters, and product warranty. To accelerate degradation, laboratory experiments are often performed at elevated temperature, voltage bias and under continuous illumination. In this study laboratory size cells (0.5 cm²), mini-modules (15 cm × 15 cm) and full-size encapsulated modules (60 cm × 120 cm) that consist of monolithically interconnected cells were subjected to different levels of illumination, elevated temperatures and electrical biases for extended periods of time. Changes in efficiency, fill-factor (FF), open-circuit voltage (V_oc) and short-circuit current (I_sc) as a function stress time and stress conditions are discussed.