We have investigated the effects of the introduction of an antireflection layer consisting of a hierarchically patterned diffraction grating into a conventional TiO₂ working electrode on the power conversion efficiency (PCE) of a DSSC. High index-contrast TiO₂ nanowires (NWs) were grown in the circular holes of the two-dimensional diffraction grating prepared through the use of a polymer template fabricated via interference lithography (IL) for maximized photon trapping effects in the visible region of light. The larger scale dimension of the polymer template was determined using the beam parameters of the IL and the smaller scale dimension in the structures was controlled by the growth conditions of the TiO₂ NWs. Compared with a conventional DSSC, the hybrid nanostructure with an additional antireflection layer demonstrated higher and wider absorption bands of wavelength spectra, leading to an increased PCE due to enhanced light trapping effects achieved by the combination of antireflection and diffraction of the light on the front surface of the devices with minimum loss in the surface area of the hierarchical structure. The excellent performance of the optimized hybrid nanostructure indicates that the nanophotonic effects have strong potential for solar energy conversion, photocatalyst, and photoelectrode applications.