Impact of thiourea concentration on the properties of sol-gel derived Zn(O,S) thin films and Cu(In,Ga)Se2 solar cells

A novel approach based on sol-gel spin coating method to deposit Zn(O,S) thin film using thiourea(TU) as a sulfur source replacing CdS as buffer layer was developed and the influence of TU concentration on the properties of Zn(O,S) thin films and Cu(In,Ga)Se-2(CIGS) solar cells were investigated in this paper. It was found by X-ray diffraction and X-ray photoelectron spectroscopy that sol-gel derived Zn(O,S) thin films were amorphous and composed of ZnS, ZnO as well as Zn(OH)(2). The variation of the optical band gap as a function of the S/(S+O) ratio was determined by energy-dispersive spectroscopy and UV-VIS-NIR. The results indicated that the minimum value for band gap of approximate 3.72 eV was obtained when the S/(S+O) = 0.44. Efficiency of up to 7.28% was achieved for a CIGS solar cell with Zn(O,S) buffer layer from 0.2M TU, which was attributed to the optimized conduction band offset (CBO) of +0.45 eV at the CIGS/Zn(O,S) interface. Zn(O, S) thin films prepared in sol-gel route was used to replace traditional CdS buffer layer deposited by chemical bath deposition method in Cu(In, Ga) Se2 solar cells. The best efficiency was achieved for CIGS/ Zn(O, S)/ i-ZnO/ ITO heterostructure solar cell with S/(S+ O) = 0.18, which was attributed to the optimized conduction band offset (CBO) of + 0.45 eV at the CIGS/ Zn(O, S) interface. [GRAPHICS] .