Rapid low-temperature solution growth of ZnO:Co nanorod arrays with controllable visible light absorption

Cobalt doped zinc oxide (ZnO:Co) nanorod arrays with strong visible light absorption were successfully grown via a solution-based method. The deposition technique presented allows rapid (1 h) growth of well aligned nanorods directly onto seed-layer coated substrates at low temperatures (ca. 85 °C), which when compared to previously reported growth methods represents a significant improvement in terms of routes to the production of visible-light absorbing ZnO-based materials. Changing the cobalt concentration in the growth solution allows the controlled growth of ZnO:Co nanorods with variable visible light absorption. The emergence of strong additional, cobalt 3d related visible light absorption features and band gap narrowing with increasing concentration of cobalt (until 20% cobalt/zinc concentration in growth solution) is demonstrated. A cobalt concentration of up to 2.2 atom% (at 30% cobalt/zinc concentration in growth solution) can be achieved and careful analysis of the crystal growth process and material properties of the nanorod arrays shows that Co²⁺ successfully replaces Zn²⁺ in the lattice.