Hydrogen in solar-grade p-type silicon: dominant complexes and solar cell efficiency

The PV market is dominated by solar cells based on mc-Si, and it is expected that Si will continue to dominate in the years to come. Huge efforts are put down in research related to improving and optimizing such silicon based photovoltaics. Practically a ll earlier solar cells based on p-type Si suffered considerable degradation under illumination. The degradation has been attributed to light-induced dissociation of the B-Fe pair. Metallic impurities are still common for modern mc-Si, and the problem of l ight-induced degradation is still very serious. In contrast, high-quality single-crystalline Si (sc-Si) is nowadays virtually free of metallic impurities. However, despite the progress, the light-induced degradation of p-type sc-Si cells still persists, a lthough due to a different mechanism. This degradation is now widely believed to be caused by carrier recombination at the B-O2 complex. H is an important impurity in Si, not only because of its presence in Si, but also because of its ability to passivat e dangling bonds of the defects, and can therefore potentially be used beneficially. Moreover, H can be introduced in Si during multiple technological steps of solar cell fabrication. The role of hydrogen is particularly important in the HIT solar cells, where a thin layer of hydrogenated amorphous Si (a-Si:H) is used. In this proposal we will (i) address the issues of hydrogen complexes in solar-grade p-type Si, particularly with boron and metallic impurities in both sc-Si and mc-Si material, and (ii) p erform predictive simulations of the effect of these complexes on the overall conversion efficiency of solar cells.