Effect of a SiO2 film on the potential-induced degradation of n-type front-emitter crystalline Si photovoltaic modules

We investigated the effect of silicon dioxide (SiO2) film in n-type front-emitter (n-FE) crystalline Si solar cells on the potential-induced degradation (PID) of n-FE photovoltaic modules. After PID tests by applying a bias of −1000 V at 85 °C for a few min, the modules with the cells without SiO2 did not degrade in the short-circuit current density and the open-circuit voltage (Voc). Since the degradation is known to be due to positive charge accumulation in SiNx films, the result suggests that such SiO2 acts as barriers to retain accumulated positive charges. After further PID tests, modules without SiO2 show faster and more significant degradation by a decreases in the fill factor (FF) and the Voc. It has been proposed that the degradation in the FF and Voc is caused by sodium (Na) introduction into cells. The results therefore suggest that SiO2 delays Na migration.