LeTID in HPMC-Si wafers studied by hyperspectral photoluminescence imaging

Light and elevated temperature induced degradation (LeTID) has become a profound problem in PERC cells, reducing performance during operation. The mechanism which governs the degradation is not fully understood, but some effect caused by hydrogen in the bulk of the cell is one of the suggested causes. High-performance multicrystalline silicon (HPMC-Si) p-type wafers of different processing have been investigated for LeTID using a hyperspectral photoluminescence imaging setup. Samples of as-cut wafers, phosphorus diffusion gettered (PDG) wafers and PDG gettered hydrogen bulk passivated (PDGH) wafers, with and without surface passivation, were processed with light soaking and elevated temperatures. LeTID was only observed in samples with both surface passivation and hydrogen bulk passivation, PDGH. This supports the hypothesis that bulk hydrogen is involved with the LeTID mechanism No specific photoluminescence (PL) in the range 0.5 – 1.3 eV was found to correlate with the LeTID. All defect related luminescence followed the same pattern as the band-to-band PL during degradation and regeneration, indicating that the LeTID defect is a non-radiative defect.