Study on Na-Ga-F compound in CIGSSe absorber prepared by CuGa-NaF target

Abstract

The CuGa-NaF target route (CNTR) is meant to enhance the efficiency of Cu(In,Ga)(S,Se)2(CIGSSe) solar cells by reducing the amount of Ga that sinks into the absorber layer. However, researchers have yet to reach a consensus as to the role of Na-Ga-F compounds and its mechanism at the interface. This study sought to elucidate the mechanism by which Na-Ga-F compounds affect the behavior of Ga at the absorber surface. In experiments, the efficiency of devices fabricated using CNTR (13.25%) was higher than that of devices fabricated using the conventional soda lime glass route (CSGR) (11.39%). It appears that the addition of F to the CNTR results in the formation of Na-Ga-F compound, which acts as an anchor for the Ga, thereby reducing the likelihood of its sinking below the surface of the absorber layer. In addition, the uniform distribution of Na in the CIGSSe absorber under the CNTR (particularly at the Mo/CIGSSe interface), was also shown to increase Voc and device efficiency. Finally, the CNTR was shown to passivate the grain boundaries, inhibit the formation of secondary phases on the surface and ameliorate interface recombination.