Cu Doping of CdTe Layers in Polycrystalline CdTe Thin-Film Solar Cells for Top Cells of Multijunction Solar Cells

The Cu doping of CdTe layers in CdTe solar cells without using a Cu-doped carbon electrode was investigated in order to develop transparent back contacts for multijunction solar cells. Cell performance was drastically improved by heat treatment after coating with Cu-doped diethylene glycol monobutyl ether (DEGBE) as compared with the cell without Cu doping. Capacitance-voltage (C-V) characteristics revealed that the acceptor concentration increased with increasing Cu concentration in DEGBE. These results suggest that Cu atoms are incorporated into the CdTe layer as acceptors by the novel Cu-doping method. Furthermore, in photoluminescence (PL) spectra of CdTe layers, the intensity of the 1.47 eV emission band was decreased by the heat treatment after coating with Cu-doped DEGBE, which suggests that the defect density is decreased by Cu doping. (C) 2013 The Japan Society of Applied Physics