Unveiling Growth and Photovoltaic Principles in Density‐Controllable TiO2 Nanorod Arrays for Efficient Solar Cells

Abstract Titanium dioxide (TiO 2 ) nanorod arrays (TiO 2 ‐NA) are widely used in optoelectronic devices. Controlling the number density ( N D ) of nanorods without altering their dimensional features in TiO 2 ‐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 D without changing the TiO 2 nanorod sizes in the rutile TiO 2 ‐NAs hydrothermally grown on an anatase TiO 2 film on a large scale. Moreover, N D ‐controllable TiO 2 ‐NAs are applied to CuInS 2 solar cells, achieving a champion efficiency of 10.44% for solution‐processed CuInS 2 solar cells. It is found that the hydrolysis time ( t H ) in preparing the anatase TiO 2 film provides good control over N D in TiO 2 ‐NA as the result of t H ‐governed nanoparticle size in the anatase TiO 2 film. A gel‐chain‐limited crystallization model for t H ‐governed anatase TiO 2 nanoparticle size, an orientation‐competing‐epitaxial nucleation/growth model for the out‐of‐plane growth of single‐crystalline rutile TiO 2 nanorod on polycrystalline anatase TiO 2 film, and a volume‐surface‐density model for the N D ‐governed photocurrent generation in nanoarray‐based solar cells are proposed.