Influence of light illumination on the potential-induced degradation of n-type interdigitated back-contact crystalline Si photovoltaic modules

Abstract

We investigate the potential-induced degradation (PID) of n-type interdigitated back-contact (IBC) crystalline Si (c-Si) photovoltaic (PV) modules under a negative bias stress and the influence of light illumination on the PID. IBC PV modules show PID characterized by a reduction in the short-circuit current density (J sc) and open-circuit voltage (V oc) under negative bias stress, while no fill factor (FF) reduction is observed. The degradation may originate from the introduction of sodium (Na) into c-Si and the resulting enhancement of carrier recombination on the surfaces of the IBC cells. Light illumination of 1 sun during the negative bias PID test results in less severe reductions of J sc and V oc. A reduction in the electric field on the surface Si nitride (SiN x ) film, due to carrier generation in the SiN x and the resulting increase in its conductivity, is a possible explanation for the mitigation of the Na-related PID.

Potential‐Induced Degradation in High‐Efficiency n‐Type Crystalline‐Silicon Photovoltaic Modules: A Literature Review

“…IBC n‐type c‐Si cells [ 35,39 ] and rear‐emitter n‐type c‐Si PV cells [ 33 ] also reportedly undergo Na‐penetration‐type PID. The former is shown in Figure 3b, and the latter is designated as a flipped structure of n‐type PERT cells shown in Figure 3a.…”

“…The EQE in a short‐wavelength range is confirmed to be reduced after PID. [ 33,39 ] In addition, the J 01 s of IBC n‐type c‐Si cells and rear‐emitter n‐type c‐Si PV cells are confirmed to be increased after Na‐penetration‐type PID. [ 33,39 ] This increase also indicates increased diffusion current via defect states originating from Na introduced in the surface region of the c‐Si wafer.…”

“…[ 33,39 ] In addition, the J 01 s of IBC n‐type c‐Si cells and rear‐emitter n‐type c‐Si PV cells are confirmed to be increased after Na‐penetration‐type PID. [ 33,39 ] This increase also indicates increased diffusion current via defect states originating from Na introduced in the surface region of the c‐Si wafer. One model has been proposed based on the formation of Na‐decorated stacking faults.…”

“…Na‐penetration‐type PID in IBC n‐type c‐Si cell modules is reportedly reduced under illumination. [ 39 ] Figure shows effects of illumination on Na‐penetration‐type PID occurring in n‐type IBC c‐Si PV cell modules. The result reveals that the illumination delays Na‐penetration‐type PID in n‐type c‐Si solar cells.…”

“…Research undertaken to investigate PID in n‐type c‐Si PV modules has gradually become active since around 2015. Some reports have described PID in PV modules fabricated from n‐type c‐Si cells, such as passivated emitter and rear totally diffused (PERT) cells, [ 16–30 ] passivated emitter and rear locally diffused (PERL) cells, [ 31 ] TOPCon cells, [ 32 ] rear‐emitter c‐Si PERT cells (with the junction not at the front‐glass side), [ 18,33,34 ] IBC cells, [ 15,35–39 ] and Si heterojunction (SHJ) cells. [ 40–43 ] According to these many studies, n‐type c‐Si PV cell modules show PID with different mechanisms from those in p‐type cells.…”