Ultrathin crystalline silicon solar cells are alternative technology roadmap to achieve more cost-effectiveness. However, when silicon thickness is reduced to less than 50 µm, light absorption loss becomes severe, especially in the long wavelength range of 900–1200 nm. Therefore, it is significant to investigate the enhancements of photocurrent and efficiency by improving light absorption in the long wavelength range. In this work, we design and fabricate approximately 20 µm-thick front-textured monocrystalline silicon solar cells. When periodic silver nanoarrays with precise geometries are applied to the rear of the solar cells, the measured external quantum efficiency clearly reveals an enhancement in the longer wavelengths. For our best sample, the short-circuit current density and the absolute efficiency present the enhancements of ΔJsc = 0.8 mA/cm2 and Δη = 0.6%.