Unveiling Growth and Photovoltaic Principles in Density-Controllable TiO Nanorod Arrays for Efficient Solar Cells.

Titanium dioxide (TiO) nanorod arrays (TiO-NA) are widely used in optoelectronic devices. Controlling the number density (N) of nanorods without altering their dimensional features in TiO-NA is of great importance to the tailored performance of the optoelectronic devices, which unfortunately remains challenging up to now. Here, a facile strategy is developed to control the N without changing the TiO nanorod sizes in the rutile TiO-NAs hydrothermally grown on an anatase TiO film on a large scale. Moreover, N-controllable TiO-NAs are applied to CuInS solar cells, achieving a champion efficiency of 10.44% for solution-processed CuInS solar cells. It is found that the hydrolysis time (t) in preparing the anatase TiO film provides good control over N in TiO-NA as the result of t-governed nanoparticle size in the anatase TiO film. A gel-chain-limited crystallization model for t-governed anatase TiO nanoparticle size, an orientation-competing-epitaxial nucleation/growth model for the out-of-plane growth of single-crystalline rutile TiO nanorod on polycrystalline anatase TiO film, and a volume-surface-density model for the N-governed photocurrent generation in nanoarray-based solar cells are proposed.