Influence of emitter position of silicon heterojunction photovoltaic solar cell modules on their potential-induced degradation behaviors

Abstract

Potential-induced degradation (PID)-test results of modules fabricated from the rear- and front-emitter silicon heterojunction (SHJ) solar cells were compared to clarify the influence of the emitter position of SHJ photovoltaic (PV) cell modules on their PID behaviors. The PID tests were performed by applying a bias of −2000 V to the shorted interconnector ribbons from the front surface of the cover glass, at 85 °C. In the initial stage, both modules showed the same degradation characterized by a reduction in the short-circuit current density (Jsc). After the first-stage degradation, the rear-emitter SHJ PV modules exhibited subsequent degradation characterized by a significant reduction in the Jsc and open-circuit voltage (Voc), due to the enhancement of the minority-carrier recombination in the front surface region of the n-type crystalline silicon base. The front-emitter SHJ PV modules, on the other hand, showed a reduction in the fill factor (FF), in addition to moderate reductions in Jsc and Voc. The FF reduction of the front-emitter SHJ PV modules is considered to be caused by the enhancement of the recombination in the front surface region of the n-type crystalline-silicon base as the region corresponds to the pn junction interface of the front-emitter configuration. The moderate reductions in both Jsc and Voc may be due to further progression of the first-stage degradation. These findings are essential for understanding the mechanism of PID in SHJ PV cell modules.