Spectral converters for CdS–CdTe solar cell

Abstract

Among thin film solar cells, CdS–CdTe solar cell is one of the earliest and most successful devise owing to high absorption co-efficient of CdTe for the solar radiations. However, the conversion efficiency drops drastically below 500 nm due to the absorption in the CdS window layer. Down shifting of 350–500 nm solar radiations is expected to overcome this drawback. It is suggested that Cr3+, Mn4+ or Sm2+ activators can provide efficient absorption of radiations in near ultraviolet (nUV)-visible region and emission around 700 nm. Synthesis and photoluminescence (PL) characterization of several such phosphors is described. Cr3+ exhibits efficient luminescence in aluminate hosts Al5GeO9.5, SrMgAl10O17:Cr, SrMgAl10O17:Eu,Cr which could be easily prepared by combustion synthesis. In oxidic hosts prepared by conventional solid state reaction; Li2Mg3SnO6:Mn4+, Mg2TiO4:Mn4+ and Ca14Zn6Al10O35:Mn4+, emission is obtained close to 700 nm where the CdS–CdTe solar cell has good response. BaAl2Si2O8:Sm2+, and BaB8O13:Sm2+ were also prepared by solid state reaction. These phosphors exhibited line emission close to 700 nm and excitation over broad spectra range. All these phosphors were characterized using XRD, photoluminescence (PL) and lifetime measurements. PL spectra are analysed in terms of Racah parameters. The PL characteristics of these phosphors are compared and it is shown that Cr3+ doped phosphors possess unwanted excitation beyond 500 nm while Mn4+ doped samples show good response either in nUV or in blue region but not both. BaAl2Si2O8:Sm2+ has optimum properties among the phosphors studied. It is suitable as a spectral converter for CdS–CdTe solar cell.