Anhui NormalUniversity researchers published a study on TiO₂ nanorod arrays (TiO₂‐NA). The research addressed the challenge of controlling nanorod number density (ND) without changing size. A scalable hydrothermal method was developed for rutile TiO₂‐NAs grown on anatase TiO₂ films. The key control parameter was hydrolysis time (tH), which governed nanoparticle size in the anatase layer. ND-controlled arrays were used in CuInS₂ solar cells, achieving a peak efficiency of 10.44%. The study proposed three models to explain the results. The first, a gel‐chain‐limited crystallization model, described tH-driven nanoparticle formation. The second, an orientation‐competing epitaxial model, explained rutile growth on polycrystalline anatase. The third, a volume‐surface‐density model, linked ND with photocurrent generation. This approach allowed structural tuning of TiO₂‐NAs without affecting dimensional features. The findings contribute to performance optimization in nanoarray-based solar devices and offer a new path for material engineering in solution-processed solar cell development.