Multicrystalline SiGe solar cells with Ge content above 10 at

摘要

In the present study we investigate the manufacturing of multicrystalline (mc) solar cells with a low germanium content using a modified Si solar cell process. For this purpose mc Si{sub}(1-x)Ge{sub}x ingots were grown in an induction heated furnace using the Bridgman technique. In this way ingots with a diameter of about 3.7 cm and a length of 4.5 cm have been obtained. The Ge concentration in the investigated samples is above 10 at%. In order to study the material properties of the obtained alloys etch pit density and resistance measurements have been performed on the SiGe wafers. Temperature dependent Hall measurements reveal acoustic phonon scattering to be the dominating scattering mechanism at room temperature while the acceptor activation energy level of boron in SiGe seems to be slightly lower than in crystalline Si. With a not yet optimized solar cell process an efficiency of 4.8% (wafer area 2.8 cm{sup}2, reflectivity > 40% at 905 nm) has been achieved. In contradiction to theoretical considerations the IQE in the long wavelength range does not exceed the one of similarly processed Si wafers. This might be caused by too small diffusion lengths within the SiGe samples.