Potential Induced Degradation Effects on Crystalline Silicon Cells with Various Antireflective Coatings

The first experiences with potential induced degradation (PID) of silicon solar cells have been presented in literature since 1989 (1-4). It has been shown that PID may cause power losses of more than 30% for modules out in the field. Critical issues on the cell level are the SiNx anti-reflective coatings (ARC), their deposition method, the emitter thickness and metallization (thus influencing the electrical series resistance). The leakage current was found as an indicator for the intensity of degradation. Moreover, different test methods to prove the stability or susceptibility of samples have been presented. In this paper we are showing the influence of the anti-reflection coating to provoke PID and the ability of silicon nitrite layers to prevent PID. For each layer structure, at least four different designs have been manufactured and tested for their stability against PID. To do so, it was necessary to find an appropriate test sequence, which would show polarization effects in an adequate time frame, while there is no standard procedure available that addresses this problem for the time being. Furthermore, it has been necessary to develop suitable reference samples to compare the results and to prove the repeatability of the test sequences. The experiment has been divided into two parts: The pre-evaluation has been realized with small one- cell mini-modules to probe the adequate testing parameters and to analyze the leakage currents for various prone samples. During the second part, we also investigated the reversibility of PID - depending on the state of degradation of these samples - to check whether PID is one 100% reversible, or whether the degradation mechanism also shows an irreversible part.