Growth and properties of SiGe multicrystals with microscopic compositional distribution and their applications for high-efficiency solar cells

The use of SiGe binary multicrystals with microscopic compositional distribution was propose as a solution to obtain new SiGe solar cells with higher conversion efficiency using the casting method. The SiGe multicrystals have many Ge-rich regions in Si-rich matrix, and this structure causes large increase of the photo-current for such SiGe multicrystal solar cells in the longer-wavelength region comparing to the Si multicrystal solar cells. The microscopic compositional distribution in SiGe multicrystals and wavelength dependence of absorption coefficient can be freely controlled. SiGe multicrystal solar cells with microscopic compositional distribution have higher efficiency than Si multicrystal solar cells mainly due to the increase of the total photo-current by a factor of 1.2, and the smaller decrease of open-circuit voltage Voc within the average Ge composition of lower than 5%. The efficiency of SiGe multicrystal solar cells has a maximum value at the average Ge composition around 5%.