Hongjie Jia

Effect of deposited temperatures of the buffer layer on the band offset of CZTS/In2S3heterostructure and its solar cell performance

The effect of the deposition temperature of the buffer layer In2S3 on the band alignment of CZTS/In2S3 heterostructures and the solar cell performance have been investigated. The In2S3 films are prepared by thermal evaporation method at temperatures of 30, 100, 150, and 200 °C, respectively. By using x-ray photoelectron spectroscopy (XPS), the valence band offsets (VBO) are determined to be , , , and eV for the CZTS/In2S3 heterostructures deposited at 30, 100, 150, and 200 °C, respectively, and the corresponding conduction band offsets (CBO) are found to be , , , and eV, respectively. The XPS study also reveals that inter-diffusion of In and Cu occurs at the interface of the heterostructures, which is especially serious at 200 °C leading to large amount of interface defects or the formation of CuInS2 phase at the interface. The CZTS solar cell with the buffer layer In2S3 deposited at 150 °C shows the best performance due to the proper CBO value at the heterostructure interface and the improved crystal quality of In2S3 film induced by the appropriate deposition temperature. The device prepared at 100 °C presents the poorest performance owing to too high a value of CBO. It is demonstrated that the deposition temperature is a crucial parameter to control the quality of the solar cells.

Characterisation and properties of Cu2ZnSnS4 thin films synthesised by sputtering from an alloy target

Cu2ZnSnS4 (CZTS) thin films were synthesised on glass substrates by sulphurising sputtered metallic precursors in H2S + N2 atmosphere at 500 °C. The influences of the radio frequency (RF) sputtering power on the structure, surface morphology, optical and electrical properties of the thin films were investigated. Scanning electron microscopy, X-ray diffraction, Raman and UV–vis NIR spectroscopy were used to characterise the films. All the CZTS thin films exhibited a dominant kesterite structure. With increasing sputtering power, secondary phases in the films reduced, and the surface became more compact. The optimum quality films with poor-Cu and rich-Zn were obtained when the sputtering power was 90 W, and the optical band gap, carrier concentration, resistivity and mobility were 1.47 eV, 2.07 × 1018 cm−3, 2.37 Ω cm and 1.38 cm2 s−1 v−1, respectively. The optical and electrical properties of the CZTS thin films in relation to the secondary phases were discussed.

Optical and Electrical Properties of Ag-Doped In2S3 Thin Films Prepared by Thermal Evaporation

Ag-doped In2S3 (In2S3:Ag) thin films have been deposited onto glass substrates by a thermal evaporation method. Ag concentration is varied from 0 at.% to 4.78 at.%. The structural, optical, and electrical properties are characterized using X-ray diffraction (XRD), spectrophotometer, and Hall measurement system, respectively. The XRD analysis confirms the existence of In2S3 and AgIn5S8 phases. With the increase of the Ag concentration, the band gap of the films is decreased gradually from 2.82 eV to 2.69 eV and the resistivity drastically is decreased from ~103 to Ωcm.