Studying the structural, optical spectroscopic ellipsometry and electrical properties of variable-CdS thickness/CdTe for solar cell applications

Abstract

"The structural and optical properties of CdS window layer at different thicknesses in the range of (100-300 nm) deposited on pre-cleaned glass substrates (CdS/glasses) via the thermal evaporation process are studied in the current work. The structural analysis is done using Rietveld refinement and atomic pressure microscope techniques. The films of CdS/glass showcase a wurtzite behavior. XRD and AFM tests are confirmed that the structural parameters improve as the thickness of the CdS-layer increases. The optical constants (the refractive index n, the extinction coefficient, k and the bandgap energy values are estimated from spectroscopic ellipsometry (SE) via the construction of an optical model. The refractive index of the CdS/glass films increases with the increase of CdS-layer thickness. This, in turn, is due to the rise of the size of the crystal in the thin layers. It is also found that as the thickness of the CdS-layer rises, so does the overall behavior of the extinction coefficient. Additionally, the bandgap energy of the direct transition decreases from 2.45 eV (d=100 nm) to 2.25 eV (d=300 nm). The dark and illumination I-V photovoltaic characteristics of fabricated devices are explored by depositing a p-CdTe thin layer (500 nm) over varying thicknesses of CdS thin films (100- 300 nm) prepared on glass substrates (2 mm) and thus, the Ni/n-CdS/i-AgSe/p-CdTe/Pt heterojunction has been successfully fabricated with an AgSe buffer layer deposited directly on the p-CdTe absorber laryer. The n-CdS window layer is deposited on i-AgSe buffer layer. In dark conditions, based on the dependence of the forward and reverse current-voltage, the essential behavior related to the fabricated diode has been determined. As well, in the illumination case, the open-circuit voltage, the short-circuit current, the fill factor, the power conversion efficiency, (PCE), photoresponsivity, quantum efficiency, dependence of generated photocurrent on the light intensity, dependence of the generated photocurrent on wavelength (λ)for the studied solar cell are computed and discussed."

Fabrication and investigation of zinc telluride thin films

“…The allowed optical energy band gap of annealed ZnTe can be calculated by the Tauc equation. since the annealed ZnTe films are polycrystalline, as shown by X-ray diffraction, the transition will most likely be permissible that is mean transition is direct [34]. This can be done by extrapolation to zero the horizontal axis hυ in the Tauc equation.…”

Effect of the back contact electrode on the performances of the ultra-thin photovoltaic cells based on the CdS/CdTe heterojunction

“…E. Artegiani et al analysed the influence of the transparent electrode on the photo-electrical response and time stability for a superstrate structure by testing an indium tin oxide/zinc oxide (ITO/ZnO) configuration compared to individual ITO and/or fluorine tin oxide (FTO) [9], while X. Mathew et al took a step forward and fabricated CdS/CdTe devices onto flexible substrates [10]. The use of different substrates was possible because both CdS and CdTe thin films can grow by assorted methods, including thermal evaporation [8,[11][12][13], radio-frequency (RF) magnetron sputtering [8,[14][15][16], close-space sublimation [17,18], electrodeposition [8,19,20], and molecular beam epitaxy [21,22]. Despite so many obtaining alternatives, the literature reports indicate thermal evaporation as the main approach and due to this, the thickness of samples is usually about 2 − 3 μm.…”