Toward an all-Atomic Layer Deposition (ALD) process for Cu(In,Ga)(S,Se)₂ (CIGS)-type solar cell

Atomic Layer Deposition (ALD) is a well-suited technique to prepare thin film heterostructures for solar cell applications. In this work, we explore the feasibility of preparing complete CIGS-type solar cells by ALD, namely the absorber layer, the buffer layer and the transparent conducting oxide window layers, with a focus on using an ultra-thin CIGS-type layer (<100 nm). The syntheses are carried out with ALD in a cross-flow reactor configuration. The materials used are the ternary material CuInS₂ as absorber layer, the In₂S₃ as buffer layer and the bilayer ZnO/ZnO:Al as window layers. Structural (by Grazing incidence XRD), optical and electrical properties are characterized as a function of the experimental deposition conditions. The thickness of In₂S₃ and the deposition conditions of the window layers have been optimized on a coevaporated 2 μm-thick CIGS absorber as reference. Results are comparable to the classical stack CdS/ZnO/ZnO:Al deposited by chemical bath deposition and sputtering. Ultra-thin film CuInS₂ (60 nm) has been then deposited and combined with the optimized ALD front layers. Preliminary results on completed solar cells are given with very low efficiency presently but paving the way of an all ALD CIGS layer route.