Micromorph Si - multicrystalline Si tandem solar cells for cost effective photovoltaics

Rigorous modeling of a micromorph Si/multicrystalline Si double junction tandem solar cells are presented. The micromorph Si (wide bandgap) solar cell was thoroughly simulated using a complete density of state model and the Si solar cell (narrow bandgap) was simulated using lifetime model. The results of these simulations were used to calculate the spectral response and conversion efficiency of the resulting Si based tandem solar cell. The dependence of the solar cell parameters (open circuit voltage, short circuit current, and conversion efficiency) on the thickness of intrinsic micromorph layer and the excess carrier lifetime in the absorber of the Si is presented. The simulation results suggest that solar cells with conversion efficiency of more than 20% are achievable using thin (100 μm) low quality Si substrate (multicrystalline Si or Si ribbon) with bulk recombination lifetime of less than 10 μsec.