Impact of different backsheets and encapsulant types on potential induced degradation (PID) of silicon PV modules

Photovoltaic (PV) modules during field exposure are subject to many durability and reliability issues, such as potential induced degradation (PID). The shunting type PID (PID-s) can significantly affect module performance. Most of the current studies on PID-s focus on understanding its mechanisms and mitigating its effects by modifying the glass, cell, or encapsulant component. Since the backsheet type influences the water vapor transmission rate, the conductivity of the encapsulant is significantly influenced by the backsheet type, and hence the level of voltage drop in the encapsulant layer during the PID stress test. The higher the conductivity of the encapsulant, the lower the voltage drop in the encapsulant and the worse the PID. Therefore, in the current work, the influence of four different backsheet types (PVF, PVDF, PA, ECTFE) and two different encapsulant types (EVA and POE) on PID is investigated. With multiple construction combinations of these materials, a set of 1-cell modules were fabricated and stressed for PID using an environmental chamber at −1000 V and 85 °C/85 %RH for 288 h. The performance and defect level changes were obtained using several pre- and post-stress characterizations, including IV and EL. The results indicate a power degradation in the range between 0 % and 9 %, depending on the backsheet-encapsulant combination. The results of this study are pertinent to understanding the influence of substrate relative to PID in PV modules. Moreover, these results can also help the manufacturers to select the best backsheet-encapsulant combination to minimize the persisting PID issues in the field.