Modeled performance of polycrystalline thin-film tandem solar cells

The optimum bandgaps for two-terminal monolithic multijunction devices have typically been studied under a fixed set of environmental conditions, using ideal device models. This study examines the effects of a realistic dark-current for typical state-of-the-art thin-film polycrystalline cells on the optimum energy gap for a series-connected two-junction cell. The optimum energy gaps are compared for a series-connected tandem cell under standard reference conditions and the energy produced for five different reference days where the temperature, spectral irradiance and total irradiance varied. The optimum bandgaps were found to be 1.72 +/- 0.02 eV for the top cell and 1.14 +/- 0.02 eV for the bottom cell. Published in 2002 by John Wiley Sons, Ltd.