Codoped ZnO films by a co-spray deposition technique for photovoltaic applications

A co-spray deposition technique has been developed to bypass a fundamental limitation in the conventional spray deposition technique, i.e., the deposition of metal oxides from incompatible precursors in the starting solution. With this technique, ZnO films codoped with F and Al have been successfully synthesized, in which F is incompatible with Al. Two starting solutions were prepared and co-sprayed through two separate spray heads. One solution contained only the F precursor, NH4F. The second solution contained the Zn and Al precursors, Zn(O2CCH3)2 and AlCl3. The deposition was carried out at 500°C on soda-lime glass in air. A minimum sheet resistance, 55.4 /, was obtained for Al and F codoped ZnO films after vacuum annealing at 400°C, which was lower than singly-doped ZnO with either Al or F. The transmittance for the codoped ZnO samples was above 90% in the visible range. This co-spray deposition technique provides a simple and cost-effective way to synthesize metal oxides from incompatible precursors with improved properties for photovoltaic applications.