Low-T anneal as cure for LeTID in Mc-Si PERC cells

Abstract

Light and elevated temperature induced degradation (LeTID) is known to be affected by the last dark anneal that the silicon wafers or cells experience prior to illumination. Here we study how low-temperature dark anneal performed on fully processed multicrystalline silicon (mc-Si) passivated emitter and rear solar cells (PERC) influences LeTID characteristics, both the intensity of the degradation and the degradation kinetics. Our results show that a relatively long anneal at 300 °C provides an efficient means to minimize LeTID while too short dark anneal at the same temperature seems to have a negative impact on the subsequent degradation under light soaking. Finally, we compare the experimental results with the model originally developed for metal precipitation and discuss the possibility of metals being involved in LeTID mechanism.

Progress in the understanding of light‐ and elevated temperature‐induced degradation in silicon solar cells: A review

“…Yli-koski et al 131 Application of a low-temperature (200 C-300 C) long duration (>18.5 h) anneal to suppress subsequent LeTID formation Varshney et al 111 Reductions in the thickness of SiN x films to reduce in-diffused hydrogen content Varshney et al 132 Implementation of ALD deposited Al 2 O 3 films as a blocking layer for hydrogen in-diffusion during firing Bredemeier et al 109 Tuning of SiN x films to high (towards 3) or low (towards 1.9) refractive indexes to reduce hydrogen mobility or density, respectively Payne et al 8,15 High intensity laser (44.8 kW/m 2 ) and high temperature process (140 C) to accelerate defect formation and recovery rates Wang et al 121 Use of single or double current injection annealing (CIA) processes (260 C, 14.5 A) on finished solar cells It may seem that from the many LeTID mitigation methods discussed above that there can be a tendency, in one way or the other, to opt for the reduction in total hydrogen concentrations within the bulk of the solar cells. 134 However, it is important to highlight the detrimental effects that this approach may represent.…”