Characterization of Cu2ZnSnSe4 (CZTSe) thin films deposited by thermal evaporation sequentially from the pure elemental sources and in-situ post annealing was carried out at 400 C under Se evaporation atmosphere. Another annealing process was applied in nitrogen atmosphere at 450 degrees C to get poly-crystalline monophase CZTSe film structure. XRD analysis together with Raman spectroscopy was used to determine the structural properties. Spectral optical absorption coefficient evaluated from transmission data showed the band gap value of 1.49 eV for annealed film. Electrical measurements indicated that CZTSe thin films have p-type semiconductor behavior with the carrier density and mobility values of 10(-19) cm(-3) and 0.70 cm(2)/(V.s). Illumination effects on the device properties of Ag/n-Si/p-CZTSe/In heterostructure were investigated by analyzing current-voltage(I-V) and frequency dependent capacitance-voltage(C-V) data. Under the illumination, Ag/n-Si/p-CZTSe/In heterostructure showed photodiode behavior having V-oc value of 100 mV and I-sc value of 27.5 mu A. With the illumination, series resistances (R-s), diode ideality factor (n) and barrier height (Phi(b)) decreased and shunt resistance (R-sh) increased. Capacitance value at lower frequency decreased due to the illumination effect. (C) 2017 Elsevier B.V. All rights reserved.