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Open AccessArticle

Pronounced Impact of p-Type Carriers and Reduction of Bandgap in Semiconducting ZnTe Thin Films by Cu Doping for Intermediate Buffer Layer in Heterojunction Solar Cells

1
Material Synthesis & Characterizations (MSC) Laboratory, Department of Physics, Fatima Jinnah Women University (FJWU), The Mall Rawalpindi 46000, Pakistan
2
Photon Science Institute (PSI), School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
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Thin Films Technology (TFT) Research Laboratory, Department of Physics, COMSATS University Islamabad (CUI), Islamabad 44000, Pakistan
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Department of Electrical Engineering, NUST College of Electrical and Mechanical Engineering, National University of Science and Technology (NUST), Islamabad 44000, Pakistan
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Analog Electronics System (AES) Laboratory, Department of Physics, Fatima Jinnah Women University (FJWU), The Mall Rawalpindi 46000, Pakistan
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Department of Physics, COMSATS University Islamabad (CUI), Islamabad 44000, Pakistan
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Department of Physics, RIPHAH International University, Islamabad 44000, Pakistan
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Department of Materials Science & Engineering, Institute of Space Technology (IST), Islamabad Highway, Islamabad 44000, Pakistan
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Department of Physics, Govt. Postgraduate College (Boys) Satellite Town, Rawalpindi 46000, Pakistan
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Department of Physics, Lahore Garrison University, Lahore 54000, Pakistan
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Department of Mathematics, COMSATS University Islamabad (CUI) Wah Campus, Wah Cantt 47040, Pakistan
*
Author to whom correspondence should be addressed.
Materials 2019, 12(8), 1359; https://doi.org/10.3390/ma12081359
Received: 11 February 2019 / Revised: 16 April 2019 / Accepted: 18 April 2019 / Published: 25 April 2019
(This article belongs to the Special Issue Interface Engineering in Organic/Inorganic Hybrid Solar Cells)
Stabilized un-doped Zinc Telluride (ZnTe) thin films were grown on glass substrates under vacuum using a closed space sublimation (CSS) technique. A dilute copper nitrate solution (0.1/100 mL) was prepared for copper doping, known as an ion exchange process, in the matrix of the ZnTe thin film. The reproducible polycrystalline cubic structure of undoped and the Cu doped ZnTe thin films with preferred orientation (111) was confirmed by X-rays diffraction (XRD) technique. Lattice parameter analyses verified the expansion of unit cell volume after incorporation of Cu species into ZnTe thin films samples. The micrographs of scanning electron microscopy (SEM) were used to measure the variation in crystal sizes of samples. The energy dispersive X-rays were used to validate the elemental composition of undoped and Cu-doped ZnTe thin films. The bandgap energy 2.24 eV of the ZnTe thin film decreased after doping Cu to 2.20 eV and may be due to the introduction of acceptors states near to valance band. Optical studies showed that refractive index was measured from 2.18 to 3.24, whereas thicknesses varied between 220 nm to 320 nm for un-doped and Cu doped ZnTe thin film, respectively, using the Swanepoel model. The oxidation states of Zn+2, Te+2, and Cu+1 through high resolution X-ray photoelectron spectroscopy (XPS) analyses was observed. The resistivity of thin films changed from ~107 Ω·cm or undoped ZnTe to ~1 Ω·cm for Cu-doped ZnTe thin film, whereas p-type carrier concentration increased from 4 × 109 cm−2 to 1.4 × 1011 cm−2, respectively. These results predicted that Cu-doped ZnTe thin film can be used as an ideal, efficient, and stable intermediate layer between metallic and absorber back contact for the heterojunction thin film solar cell technology. View Full-Text
Keywords: semiconductor thin films; CSS; ion-exchange; XRD; SEM; p-type carriers; band gap; solar cell semiconductor thin films; CSS; ion-exchange; XRD; SEM; p-type carriers; band gap; solar cell
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Mahmood, W.; Awan, S.U.; Ud Din, A.; Ali, J.; Nasir, M.F.; Ali, N.; ul Haq, A.; Kamran, M.; Parveen, B.; Rafiq, M.; Abbas Shah, N. Pronounced Impact of p-Type Carriers and Reduction of Bandgap in Semiconducting ZnTe Thin Films by Cu Doping for Intermediate Buffer Layer in Heterojunction Solar Cells. Materials 2019, 12, 1359.

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