Direct observation of changes in the effective minority-carrier lifetime of SiNx-passivated n-type crystalline-silicon substrates caused by potential-induced degradation and recovery tests

We directly observed reductions in the effective minority-carrier lifetime (τeff) of n-type crystalline silicon (c-Si) substrates with silicon-nitride passivation films caused by potential-induced degradation (PID). We prepared PID-test samples by encapsulating the passivated substrates with standard photovoltaic-module encapsulation materials. After PID tests applying − 1000 V to the c-Si samples from the glass surface, the τeff was decreased, which probably pertains to Na introduced into the c-Si. After PID tests applying + 1000 V, the sample, on the other hand, showed a considerably rapid τeff reduction, probably associated with the surface polarization effect. We also performed recovery tests of predegraded samples, by applying a bias opposite to that used in a degradation test. The τeff of a sample predegraded by applying + 1000 V was rapidly completely recovered by applying − 1000 V, while those of predegraded by applying − 1000 V show only slight and insufficient τeff recovery.