Atomic Layer Deposition of zinc oxide for solar cell applications

• We have grown ZnO thin films using Atomic Layer Deposition (ALD).
• We demonstrate that very uniform and smooth films can be obtained, with excellent structures.
• We demonstrate that aluminum doped can be achieved, with an optimum Al concentration of 5%.

Atomic Layer Deposition (ALD) is a vapor phase thin film deposition technique, performed at low substrate temperatures, which enables the deposition of extremely uniform thin films. This technique is scalable up to very large substrates, making it very interesting for industrial applications. On the other hand, ZnO, both undoped and aluminum doped is commonly used as a transparent electrode in solar cells based on Cu(In,Ga)Se2 (CIGS), and is usually deposited by Physical Vapor Deposition techniques. In this paper, we investigate the potential of ALD for the deposition of ZnO windows for solar cell applications. Thin films of a few hundreds of nanometers were grown by ALD, both undoped and doped with aluminum. They were studied by X-ray diffraction, electrical transport measurements, Atomic Force Microscopy and transmittance experiments.