Analytical modelling of via-associated recombination losses in MWT solar cells

Two new analytical models are presented in this framework. The first model deals with calculation of the local via recombination velocity Svia from photoconductance lifetime measurements. The second model relates Svia to loss in VOC by solving the diffusion equation in two-dimensions. From short-loop tests, we show that these analytical models are valid over a wide range of via densities. The results also show that alkaline etching treatment after the laser via drilling step reduces Svia by an order of magnitude and thus allows for good via passivation. We then make use of these models for estimating VOC loss in our MWT solar cells as a result of via recombination. We find that via recombination losses can be substantial at high via densities and so by limiting the number of vias on large area cells (239 cm2) and with good via passivation, the VOC loss can be limited to ~ 1 mV. This finding is in agreement with our cell integration results.