Indium-based interface chemical engineering by electrochemistry and atomic layer deposition for copper indium diselenide solar cells

The key to achieve better Cu(In, Ga)Se₂ (CIGS) cells is through the improvement of the CIGS/ZnO interface. In this work, we illustrate various approaches, wet and dry, to engineer that interface with processes that avoid the use of Cd containing compounds. Wet chemical treatments have been performed so as to test the possibility to improve that interface by surface doping of CIGS. X-ray photoelectron spectroscopy (XPS) and Kelvin probe studies show that such doping is not achieved in the conditions leading to best devices. Rather, the most desirable feature of the surface treatments appears to be surface passivation. We show that this can be achieved via CIGS surface reaction with In(III) ions, leading to 12.5% efficient devices. A well passivated interface can also be achieved directly, using an all dry process, by Atomic Layer Deposition (ALD) of In₂S₃ buffer layer, yielding to 13.5% efficient devices. The ALD growth of the buffer layers have been studied in situ with the help of a quartz crystal microgravimetry.