Cuprous sulphide was deposited on p-type silicon substrate by thermal evaporation technique to form Cu2S film / p-Si heterojunction, and deposited on glass to measure the thermoelectric power. The thickness of Cu2S film is (d = 113 nm), the structure of Cu2S thin film investigated by X-Ray diffraction (XRD). XRD pattern shows that the powder of Cu2S has a polycrystalline nature and also the thin film. By indexing the peaks, Cu2S is defined as orthorhombic crystal system with lattice parameter [a=11.82 Å, b= 27.05 Å, c =13.43Å]. Surface morphology and grain size has been obtained by transmission electron microscope (TEM). TEM) for a deposited Cu2S thin film shows a nanocrystalline structure with average grain size 43 nm. .The thermo electric power of Cu2S thin film was obtained and the seeback is positive refers to a p-type semiconducting. The calculated rectification ratio at 1 volt for the investigated device was found to be 4.3 at room temperature. I-V characteristic in dark at temperature from 393 to 373 Kelvin has been investigated. I-V characteristic in illumination at light intensity from 1400 to 22000 Lux has been investigated by change the distance between the light source and the sample. The I-V curves exhibited diode like behavior the obtained value of series resistance (Rs) was 104KΩ. The quality factor shows that the thermionic emission is the operating mechanism.
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