$Cu_2O$ nanoparticles-based films are fabricated by spin-coating on glass substrates and their optoelectronic characteristics are investigated in this study. The $Cu_2O$ films are nearly all-transparent as high as 98% in a wavelength range from 400 nm to 900 nm and three exciton peaks associated with the sublevels in the conduction band are observed at the wavelengths shorter than 400 nm in the absorption spectrum. Under the illumination of the 325 nm wavelength light, the photocurrent efficiency of the $Cu_2O$ film is $1.8 imes10^5 {mu}A/W$ at a voltage of 2.5 V in air.