Band offset in zinc oxy-sulfide/cubic-tin sulfide interface from X-ray photoelectron spectroscopy

摘要

Zinc oxy-sulfide, ZnOxS1-x, has been found to provide better band alignment in thin film solar cells of tin sulfide of orthorhombic crystalline structure. Here we examine ZnOxS1-x/SnS-CUB interface, in which the ZnOxS1-x thin film was deposited by radio frequency ( rf) magnetron sputtering on SnS thin film of cubic ( CUB) crystalline structure with a band gap (E-g) of 1.72 eV, obtained via chemical deposition. Xray photoelectron spectroscopy provides the valence band maxima of the materials and hence placesthe conduction band offset of 0.41 eV for SnS-CUB/ZnO0.27S0.73 and -0.28 eV for SnS-CUB/ZnO0.88S0.12 interfaces. Thin films of ZnOxS1-x with 175-240 nm in thickness were deposited from targets preparedwith different ZnO to ZnS molar ratios. With the target of molar ratio of 1: 13.4, the thin films are of composition ZnO0.27S0.73 with hexagonal crystalline structure and with that of 1: 1.7 ratio, it is ZnO0.88S0.12. The optical band gap of the ZnOxS1-x thin films varies from 2.90 eV to 3.21 eV as the sulfur to zinc ratio in the film increases from 0.12: 1 to 0.73: 1 as determined from X-ray diffraction patterns. Thus, band offsets sought for absorber materials and zinc oxy-sulfide in solar cells may be achieved through a choice of ZnO: ZnS ratio in the sputtering target. (C) 2016 Elsevier B. V. All rights reserved.