Unraveling bulk defects in high-quality c-Si material via TIDLS

The current trend in silicon photovoltaics moving towards high-quality thin mono-crystalline silicon substrates sets a new challenge for the understanding of recombination mechanisms limiting the final performance of solar cells. Temperature-and injection-dependent lifetime spectroscopy (TIDLS) has been shown to be a promising method for studying of high-quality material with lifetime above 10ms where the concentration of electrically active defects is well below the sensitivity of the most well-known characterization techniques. In particular, when coupled with the Shockley-Read-Hall lifetime recombination model, TIDLS is capable of providing the most important defects' parameters including their energy level and concentration. In this contribution, we show that for a high-quality silicon material, a thorough evaluation of the surface recombination velocity (SRV) temperature-and injection dependence is crucial for an accurate identification of the defects contained in the bulk. A new methodology for the analysis of TIDLS data, called defect parameters contour mapping, is introduced for the first time. By applying it to high-quality n-type float zone c-Si samples passivated by a-Si:H(i) or an a-Si:H(i)/a-Si:H(n) stack, we are able to assert the presence of defects in high lifetime materials in a range of concentration unachievable by any other characterization technique thus far. (C) 2016 John Wiley & Sons, Ltd.