Electrodeposition of group-IIIA doped ZnO as a transparent conductive oxide

Electrodeposition of Group-IIIA (Al and Ga) doped ZnO with resistivity as low as 3.8×10^-4 Ω-cm is reported here. This ZnO can be used as an "on-top" transparent conductive oxide which is deposited on semiconductors in thin-film solar cells such as amorphous Si, CIGS, and organic cells. In addition to low cost, high throughput, and large-area processing, electrodeposition provides advantages other solution-based deposition techniques do not offer, including precise and in-line control of the film thickness. After post-deposition annealing, Al-doped ZnO achieves a resistivity of 8×10^-4 Ω-cm and Ga-doped ZnO 3.8×10^-4 Ω-cm, respectively. The doping mechanism is believed to be coprecipitation of ZnO with Al₂O₃ or Ga₂O₃ in the aqueous solution, leading to Al or Ga substitution of Zn in the ZnO lattice as n-type dopant. Both Al-doped and Ga-doped ZnO shows high transmittance above 80% for films of ∼450 nm thick.