Sputtered In_x(O,S)_y Buffer Layers for Cu(In,Ga)Se₂ Thin-Film Solar Cells: Engineering of Band Alignment and Interface...

We propose a simple approach to engineering the sputtered In_x(O,S)_y/Cu(In,Ga)Se₂ heterojunction, in terms of band alignment and interface properties. The band alignment was tailored by tuning the base pressure of the sputtering deposition to incorporate oxygen into deposited In₂S₃ layers (termed as In_x(O,S)_y). The interface properties were improved by optimizing the air-annealing temperature on In_x(O,S)_y/Cu(In,Ga)Se₂ stacked layers. Increasing the base pressure raises the O/(S + O) ratio contained in deposited In_x(O,S)_y films and thus widens the band gaps. This could effectively tailor the conduction band offset (ΔE_C) at the In_x(O,S)_y/Cu(In,Ga)Se₂ interface from a cliff (-0.25 eV) to a nearly flat band (0.07 eV) alignment. On the other hand, the extra air annealing at 235 °C did not significantly change the band alignment but did ameliorate the interface properties by reducing the Cu content at the Cu(In,Ga)Se₂ surface and diminish the interface defect density induced by sputtering damages. The former might enhance the type of inversion and increase the hole barrier at the interface, preventing the detrimental recombination behavior. The latter could effectively strengthen the junction quality. Consequently, our approach substantially enhances the cell efficiency from 2.30% to 11.04%.