Potential-induced degradation of Cu(In,Ga)Se₂photovoltaic modules

Abstract

Potential-induced degradation (PID) of Cu(In,Ga)Se 2 (CIGS) photovoltaic (PV) modules fabricated from integrated submodules is investigated. PID tests were performed by applying a voltage of %1000 V to connected submodule interconnector ribbons at 85°C. The normalized energy conversion efficiency of a standard module decreases to 0.2 after the PID test for 14 days. This reveals that CIGS modules suffer PID under this experimental condition. In contrast, a module with non-alkali glass shows no degradation, which implies that the degradation occurs owing to alkali metal ions, e.g., Na + , migrating from the cover glass. The results of dynamic secondary ion mass spectrometry show Na accumulation in the n-ZnO transparent conductive oxide layer of the degraded module. A CIGS PV module with an ionomer (IO) encapsulant instead of a copolymer of ethylene and vinyl acetate shows no degradation. This reveals that the IO encapsulant can prevent PID of CIGS modules. A degraded module can recover from its performance losses by applying +1000 V to connected submodule interconnector ribbons from an Al plate placed on the test module.

Comprehensive study of potential‐induced degradation in silicon heterojunction photovoltaic cell modules

“…PID in SHJ PV modules was found to be effectively prevented by the use of an ionomer encapsulant, demonstrating that the high reliability of SHJ PV modules can be further improved by using encapsulants with a high electrical resistance. This protective effect is already well known for preventing PID in other types of PV modules; this effect is in part caused by the suppression of Na migration. The PID‐suppression effect observed in this study is likely caused by a significant reduction in Na migration, which is consistent with the proposed mechanism presented in Section .…”

“…It has been reported that PID in many types of PV modules including p‐type c‐Si, n‐type front‐emitter c‐Si, and CIGS modules can be recovered by applying the opposite bias to that used in the degradation tests. To investigate whether such a regeneration effect occurs for the PID in SHJ PV modules, we applied a positive bias of +1000 V to a degraded module.…”

“…To determine a possible measure for preventing PID in SHJ PV modules, we performed the PID tests on an SHJ PV module using an ionomer encapsulant, which has a considerably higher volume resistivity (10 16 Ω cm) compared with that of the EVA encapsulant used in this study. Thanks to their high volume resistance, ionomer encapsulants can effectively prevent PID from occurring in several kinds of PV modules, such as p‐type c‐Si, n‐type front‐emitter c‐Si, and CIGS PV modules. Figure shows the dependence of P max / P max,0 of the SHJ PV modules with the standard EVA encapsulant and with the ionomer encapsulant on the PID testing duration.…”

“…Further, all the bias, temperature, and humidity conditions were the same as those used in this study. After 1 day of PID testing, the P max / P max,0 value of the a‐Si, CIGS, and n‐type rear‐emitter c‐Si PV modules decreased to 0.23, 0.95, and 0.93, respectively. When the PID tests were 2 days long, however, the P max / P max,0 for the p‐type c‐Si and n‐type front‐emitter c‐Si PV modules decreased to 0.04 to 0.4 and 0.85, respectively.…”

“…We have previously reported PID test results for PID‐prone p‐type c‐Si, conventional superstrate‐type a‐Si thin‐film, CIGS thin‐film, n‐type front‐emitter c‐Si, and n‐type rear‐emitter c‐Si PV modules. Except for the a‐Si thin‐film module, these PV modules had the same module configuration and the same encapsulation materials (the a‐Si thin‐film module had a superstrate configuration; thus, there was no encapsulant between the front glass and the cells).…”