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 10 ms 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.