Serial cosputtering for aluminum doping manipulated zinc oxide as front contact for Cu(In,Ga)Se2 solar cells

Abstract

Aluminum zinc oxide (AZO) thin films were deposited by modified in-line direct current magnetron sputtering — so-called serial cosputtering — using two commercial rotatable targets. A metallic aluminum target (secondary target) was used to condition the surface of a rotatable ceramic aluminum-doped zinc oxide target (ZnO:Al2O3 wt %) as the primary target from which the film was deposited. Consequently, the direct current power applied to the secondary target enabled the variation of doping concentration in the deposited film. An optical transmittance >80% with an improved resistivity (<10−3 Ω·cm) and a higher carrier concentration (3 × 1020–6 × 1020 cm−3) were demonstrated in 300-nm-thick AZO thin films. AZO films with 2.23 at. % aluminum concentration used as the transparent conductive oxide (TCO) layer in copper indium gallium diselenide (CIGS) solar cells showed the best results with an efficiency of up to 13.2% due to an improved fill factor. The results reveal that adjusting the aluminum concentration could be used to match the electrical and optical characteristics of the TCO layer to those of the solar cells.