Light-induced Degradation of Silicon Solar Cells with Aluminiumoxide Passivated Rear Side

Abstract

Light-induced degradation (LID) has been shown to significantly affect the performance of multicrystalline silicon (mc-Si) solar cells with aluminium oxide (AlOx) passivated rear side. Within this work, the impact of LID on the conversion efficiency of different silicon solar cell architectures with and without AlOx passivation is investigated. Under conditions representing realistic module operation, significant light-induced degradation of up to = -2.9 % rel in conversion efficiency has been observed for multicrystalline silicon (mc-Si) solar cells with AlOx passivation. This degradation has been found to be higher than the degradation of, both, a mc-Si aluminium back surface field (Al-BSF) solar cell and, remarkably, a Czochralski-grown silicon (Cz-Si) solar cell with AlOx passivation. For a more detailed investigation of the interaction of mc-Si and AlOx passivation during degradation, a photoluminescence-based "effective defect" imaging has been performed on AlOx-passivated mc-Si lifetime samples. The local effective defect lifetime related to recombination due to LID-induced defects is found to vary strongly in the range of eff,defect = 5 to 75 μs and, furthermore, areas with low effective lifetime could be identified as areas with relatively high dislocation density.

Lifetime degradation and regeneration in multicrystalline silicon under illumination at elevated temperature

“…5,6 The degradation was observed to a lesser extent on solar cells with a full-area aluminum back surface field (Al-BSF). Similar results were more recently reported by Fertig et al, 7,8 who described the degradation of mc-Si passivated emitter and rear cells (PERC) on even larger timescales at 0.15 suns and 70…”

Possible Candidates for Impurities in mc‐Si Wafers Responsible for Light‐Induced Lifetime Degradation and Regeneration

“…Since they were not able to explain this effect by known light‐induced degradation processes such as the boron‐oxygen defect activation or the iron‐boron pair dissociation, they attributed the efficiency loss to a new degradation mechanism. The increasing number of studies on this phenomenon in recent years underlines the practical and fundamental relevance of the effect, which is sometimes denoted “LeTID” (Light and elevated Temperature Induced Degradation) . In order to elucidate the fundamental degradation mechanism, we recently performed a comprehensive lifetime study where we showed that (i) after completed degradation, a full regeneration of the lifetime is observed on a timescale of several hundred hours, (ii) the degradation/regeneration cycle is trigged by a rapid thermal annealing (RTA) treatment and no degradation is observed with no or a low‐temperature RTA treatment, and (iii) the thinner the mc‐Si wafer the faster the regeneration appeared to take place.…”

Degradation and regeneration analysis in mc-Si

“…The degradation of lifetime samples has been demonstrated by [3], but no regeneration has been observed. In case of [4], lifetime samples were used to calculate so called effective defect lifetime maps by comparing the initial and degraded effective minority charge carrier lifetime ( eff ) distribution. The influence of different temperatures during firing on the degradation and regeneration behavior of lifetime samples is discussed in [5].…”