Defect density and recombination lifetime in microcrystalline silicon absorbers of highly efficient thin-film solar cells determined by numerical device simulations

The absorber layers of microcrystalline silicon thin-film solar cells with p-i-n structure deposited by plasma-enhanced chemical vapor deposition at 200degreesC are characterized regarding the defect density and the recombination lifetime. The characterization is based on a comparison of experimentally determined solar cell characteristics with results from numerical device simulations. Evaluation of the dark reverse saturation current indicates a strong dependence of the recombination lifetime tau on the hydrogen dilution during the deposition. Close to the transition region to amorphous growth, where the highest solar cell efficiencies are observed, tau is maximum within the crystalline deposition regime and equals around 80 ns. The aspect of a spatially varying defect density within the absorber layer is also addressed by numerical simulations. The results from the analysis of the dark current are compared with electron spin resonance data determined on single layers, which allows conclusions to be drawn regarding the capture cross section of the dominant recombination site in microcrystalline silicon. (C) 2003 American Institute of Physics.