Potential-induced degradation of thin-film Si photovoltaic modules

Abstract

Potential-induced degradation (PID) of thin-film Si photovoltaic (PV) modules was investigated. The characteristics of PID phenomena of thin-film Si PV modules are markedly different from those of crystalline Si PV modules. Not only performance loss but also linear-shape and spot-shape delamination was observed after negative voltage application. Recovery from PID was also observed after positive voltage application. However, rapid progression of PID was found after the second negative voltage application after recovery from the initial PID. The root cause of PID of thinfilm Si PV modules is thought to be the delamination between a transparent conductive oxide film and a glass substrate. Such degradation accompanied by delamination was also observed in thin-film Si PV modules exposed outside for about 5 years.

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

“…This, too, suggests that there was no significant increase in the recombination losses. This PID, mainly caused by optical losses, is different from all the other PID-related phenomena reported so far (while PID in thin-film a-Si PV modules is partly affected by additional optical losses, other loss mechanisms dominate 25 ). A possible reason behind the reduced J sc will be discussed in detail in Section 4.2.…”

“…It has been reported that various kinds of PV cells, such as conventional p-type c-Si, [10][11][12][13][14] n-type front-emitter c-Si, [15][16][17][18][19] n-type rear-emitter c-Si, 19,20 n-type IBC c-Si, 22 a-Si thin-film, 24,25 CIGS thinfilm, [26][27][28] and CdTe thin-film 28,29 PV cells, undergo PID under negative bias. Herein, we first clarified how the J-V, EQE, and EL characteristics of SHJ PV modules change upon applying a negative bias.…”

“…PID, which occurs in several different types of PV modules under negative bias, such as in conventional p-type c-Si, 10-14 n-type rear-emitter c-Si, 20 n-type IBC c-Si, 22 a-Si, 24,25 CIGS, [26][27][28] and CdTe 28,29 PV modules, has been associated with Na. SHJ PV modules were found to undergo PID under negative bias; thus, it is likely that Na plays an important role.…”

“…PID is a type of performance deterioration that is triggered by the difference in the electric potential between the grounded frame and the cells and is found mainly in large-scale PV systems, as the system bias in such installations is very high. PID reportedly occurs in numerous different kinds of PV modules fabricated from conventional p-type c-Si cells [10][11][12][13][14] ; conventional n-type c-Si cells [15][16][17][18][19] ; n-type c-Si cells with rear-side emitters 19,20 ; n-type IBC cells, 21,22 including those with front floating emitters 23 ; thin-film a-Si cells 24,25 ; copper indium gallium selenide (CIGS) thin-film cells [26][27][28] ; and cadmium telluride (CdTe) thin-film cells. 28,29 Since the degradation behavior of PV modules is known to strongly depend on their cell and module structures, PID should be investigated for each type of PV module.…”

Effect of light irradiation during potential-induced degradation tests for p-type crystalline Si photovoltaic modules

“…If the encapsulant with a relatively low volume resistivity on the order of 10 14 Ω cm, such as ethylene-vinyl acetate (EVA), is used, leakage current flows from the Al frame to the PV cells accompanied by a drift of Na from the cover glass to the PV cell. Such Na drift by a high electric field and migration to the pn junction in the PV cells are one of the possible origins of PID for p-type crystalline Si PV modules, [4][5][6][7] although PID is merely a generic name for the degradation induced by the potential difference between the Al frame and the PV cells, and the degradation behavior and mechanism of PID are essentially different for different types of PV cells: for p-type crystalline Si, 1,2,7,8) possibly due to the migration of Na; for n-type crystalline Si, [9][10][11][12] possibly due to charge recombination; for Si heterojunction, 13,14) due to the reduction of transparent conductive oxide (TCO) layer; thin-film Si, 15) due to the delamination of the TCO layer, Cu(In,Ga)Se 2 , 16,17) CdTe, 18) and others. Such mechanisms are still controversial in spite of much effort using various kinds of tools and techniques devoted to clarifying the main origins of PID.…”