Deposition of ZnO thin films from aqueous solution in a low power plasma reactor

• The low power plasma reactor is a fast deposition technique with high growth rates.
• The final optimizations allow high average growth rates reaching 0.6 nm·s− 1.
• The ZnO films are made by spraying a nitrate solution through cold plasma.
• Characterization results show a good crystallinity, composition and transparency.
• CIGS solar cells with a plasma sprayed i-ZnO layer show efficiencies around 15%.

The deposition of zinc oxide (ZnO) as a window layer in CuInGa(S,Se)2 (CIGS) thin film solar cells was studied in a low power plasma reactor. This deposition technique was used to obtain intrinsic ZnO thin layers from zinc nitrate Zn(NO3)2 precursors dissolved in water. The liquid solution was injected under a spray form into oxidant plasma at low power (135 W) to be transformed into a ZnO coating deposited onto a substrate. The deposited ZnO films were analyzed to determine the electrical, optical and structural properties (SEM, XRD, FTIR, UV–vis, 4-point probes method). Analysis showed that the thin films were adherent, transparent, homogenous and crystallized under a Würtzite form. This was in accordance with the required properties for a window layer in CIGS solar cells. In addition, the growth rate of ZnO was determined from micrographs to be equal to 0.61 nm s− 1 in the plasma reactor. This value was compared with the growth rate of usual ZnO deposition techniques and was found to be the highest. This proved that this plasma reactor working at low power is very promising for the deposition of thin films for industrial CIGS application.