Sputtered In-x(O,S)(y) Buffer Layers for Cu(In,Ga)Se-2 Thin-Film Solar Cells: Engineering of Band Alignment and Interface Properties

摘要

We propose a simple approach to engineering the sputtered In-x(O,S)(y)/Cu(In,Ga)Se-2 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)Se-2 stacked layers. Increasing the base pressure raises the O/(S + 0) ratio contained in deposited In-x(O,S)(y) films and thus widens the band gaps. This could effectively tailor the conduction band offset (Delta E-C) at the In-x(O,S)(y)/ Cu(In,Ga)Se-2 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 degrees C did not significantly change the band alignment but did ameliorate the interface properties by reducing the Cu content at the Cu(In,Ga)Se-2 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%.