1.7 eV MgCdTe double-heterostructure solar cells for tandem device applications

MgxCdi-xTe/Si tandem cells have the potential to reach a conversion efficiency greater than 40%. MgxCd1-xTe /MgyCd1-yTe (y>x) double heterostructures (DHs) grown by molecular beam epitaxy exhibit ~1.7 eV bandgaps and very high absorption coefficients, as measured using photoluminescence (PL) and spectroscopic ellipsometry. Indium-doped n-type MgxCd1-xTe (x ~ 13% Mg mole fraction) with a ~1.7 eV bandgap shows strong PL, comparable to that from high-quality CdTe/MgCdTe double heterostructures. Devices consisting of an n-type MgxCd1-xTe DH absorber, a p-type hydrogenated amorphous silicon (a-Si:H) hole contact layer and an indium tin oxide (ITO) top electrode are demonstrated with promising performance.