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Two-dimensionally (2D) arrayed hemispherical nanostructures of TiO 2 thin films were successfully fabricated using a simple procedure of spin-coating or dip-coating TiO 2 nanoparticles onto 2D close-packed polystyrene (PS) nanospheres, followed by PS extraction. The nanostructured TiO 2 film was then used as an n-type layer in a lead sulfide (PbS) colloidal quantum dot solar cell. The TiO 2 nanostructure could provide significantly increased contacts with subsequently deposited PbS quantum dot layer. In addition, the periodically arrayed nanostructure could enhance optical absorption of the cell by redirecting the path of the incident light and increasing the path length passing though the active layer. As a result, the power conversion efficiency (PCE) reached 5.13%, which is approximately a 1.7-fold increase over that of the control cell without nanostructuring, 3.02%. This PCE enhancement can mainly be attributed to the increase of the short-circuit current density from 19.6 mA/cm 2 to 30.6 mA/cm 2 , whereas the open-circuit voltage and fill factor values did not vary significantly. [ABSTRACT FROM AUTHOR]