Successive ionic layer adsorption and reaction (SILAR) is a modified version of chemical bath deposition (CBD) method, in a way that substrate is immersed in cationic and anionic precursors, alternatively and film growth takes place only on the substrate surface. SILAR method is employed to deposit copper (I) iodide as solar cell window material at room temperature (25°C). Glass and CuInS2 (CIS) are used as substrates. Deposition conditions for Cul are optimized on glass substrate and the same are used on CIS. On both the substrates, structure of Cul is Zinkblende with γ-phase. Surface morphology of Cul is crystalline on glass substrate while fibrous on CIS, which converts to crystalline after wet chemical iodine treatment at room temperature. On the glass substrate, these film exhibit transmission over 75 % in the wavelength range 400-800 nm with the optical band gap of 2.97 eV for 300 nm thickness. Device completion was made for Cul (before and after iodine treatment) on CIS and photovoltaic parameters are reported.