Anatase/Rutile nucleation and growth on (0002) and (11-20) oriented ZnO:Al/glass substrates at 150 °C

• ZnO:Al thick layers were grown with [0001] or [11-20] preferential orientation.
• Nanocrystalline TiO2 layers were deposited on ZnO:Al at temperature as low as 150 °C.
• Anatase was selectively formed during deposition on the [0001] oriented substrate.
• Anatase and rutile are in competition on the [11-20] oriented substrate up to 650 °C.
• Anatase selectivity is proposed for dye sensitised solar cell applications.

TiO2/ZnO:Al (AZO) bilayers were grown by DC reactive sputtering at temperature below 200 °C. The AZO structure was tuned in such a way that (0002) and (11-20) preferentially oriented and fiber textured domains were formed. The TiO2 layers grown at 150 °C on those two kinds of substrates are partially crystalline (and not amorphous as expected) in a composition which is substrate-dependent. Anatase was selectively formed on (0002) oriented AZO substrates after deposition, and maintained for annealing temperatures up to 650 °C. A mixture of anatase and rutile has instead nucleated and grown on the (11-20) oriented AZO substrate, with their relative amount changing by increasing the annealing temperature. Anatase selectivity and also its nucleation at low temperature are promising issues to realise flexible dye sensitised solar cells.