Semi-Analytical Modeling of the Recombination at the a-Si/c-Si Interface of Heterojunction Silicon Solar Cells: A Better Physical Insight

A semi-analytical model is proposed for carrier recombination at the amorphous silicon-crystalline silicon interface in HIT high efficiency p + a-Si/c-Si silicon solar cells. PC1D simulations indicate that pn junction is shifted inside the c-Si substrate by the effect of holes spilling over the heterojunction. Front surface field passivation is found more effective in cells without intrinsic a-Si spacer as a result of the higher hole interface concentration. Increasing the p + a-Si doping level leads to further increase in the hole interface concentration but finally deteriorates the bulk lifetime in the induced p + c-Si emitter which lowers the open circuit voltage. Such effect is less pronounced in cell with a spacer because the hole interface concentration saturates at 3x10 19 /cm 3 . In addition the spacer provides an interface with better properties and hence reduced recombination. A coupled semi-analytical/ PC1D simulations method is developed to deal with the interdependence between the calculated surface recombination velocity and the numerically simulated carrier concentrations at the interface. ShockleyRead-Hall recombination and amphoteric three charge state recombination more appropriate for recombination via dangling bonds in a-Si are considered. It is found that when the capture cross sections are equal, SRH and amphoteric recombination converge. On the other hand, SRH strongly underestimates the interface recombination velocity if the values of capture cross sections are largely distant.