K2GeF6:Mn4+ phosphor for improving performance of CdS-CdTe solar cells

Cadmium telluride PV is the only thin film technology with lower costs than conventional solar cells made of crystalline silicon in multi-kilowatt systems. The CdS-CdTe solar cell has a high conversion efficiency as well as capability to be produced at low cost. The heterojunction CdS-CdTe solar cell shows a high spectral response in the wavelength region from 500 nm with a sharp rise to 850 nm, while it is much less sensitive for the region below 500 nm due to the absorption in the CdS window layer. Accordingly, if sunlight in the wavelength region below 500 nm can be somehow used for the extension of the spectral response, then an increase of short-circuit current which leads to the increase of both output power and conversion efficiency will be achieved. This can be done by using downshifting phosphors which can absorb light in the region 300-500 nm and emit at longer wavelengths. Synthesis and characterization of one such phosphor viz. K2GeF6:Mn4+ is described in the present paper.