Electronic effect of Na on Cu(In,Ga)Se2 solar cells

We report the effect of Na on the electronic properties of Cu(In,Ga)Se-2 (CIGS) thin-film solar cells with a structure of grid/ITO/i-ZnO/CdS/CIGS/Mo/SiOx/soda-lime glass (SLG). The diffusion of Na from the SLG into the CIGS layer was systematically controlled by varying the thickness of SiOx. As the Na content increased, the hole concentration of CIGS was enhanced, while the band-gap was nearly constant, which led to a lower Fermi level in the CIGS towards its valence-band edge. The Na-induced increment in the built-in potential (V-bi) across the n-(ITO/i-ZnO/CdS)/p-CIGS junction yielded an increment of open-circuit voltage that well agreed with the calculated V-bi. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733679]