Near-infrared (NIR) photodetectors have interesting roles in optical fiber communications and biomedical applications. Conventional NIR photodetectors have been realized using InGaAs and Ge, of which the cut-off wavelengths exceed 1500 nm. Si-based photodetectors exhibit limited external quantum efficiency at wavelengths longer than 1000 nm. By synthesizing a CuInSe₂ compound on a glass substrate, photodetectors that can detect optical wavelengths longer than 1100 nm have been realized in this study. The bandgap energies of the CuInSe₂ thin films were tuned by varying the Cu/In ratio from 1.02 to 0.87. The longest cut-off wavelength (1309 nm) was obtained from a CuInSe₂ thin film having a Cu/In ratio of 0.87. The responsivity of the photodiode was measured under the illumination of a 1064 nm laser light. The photo responses exhibited linear response up to 2.33 mW optical illumination and a responsivity of 0.60 A/W at −0.4 V.