Optical and electrical properties of copper-incorporated ZnS films applicable as solar cell absorbers

M. Mehrabian; Z. Esteki; H. Shokrvash; G. Kavei

doi:10.1088/1674-4926/37/10/103002

J. Semicond. > 2016, Volume 37 > Issue 10 > 103002

SEMICONDUCTOR MATERIALS

Optical and electrical properties of copper-incorporated ZnS films applicable as solar cell absorbers

M. Mehrabian^1,, Z. Esteki², H. Shokrvash² and G. Kavei³

+ Author Affiliations

Corresponding author: M. Mehrabian, Email: masood.mehrabian@yahoo.com

DOI: 10.1088/1674-4926/37/10/103002

Abstract: Un-doped and Cu-doped ZnS (ZnS:Cu) thin films were synthesized by Successive Ion Layer Absorption and Reaction (SILAR) method. The UV-visible absorption studies have been used to calculate the band gap values of the fabricated ZnS:Cu thin films. It was observed that by increasing the concentration of Cu²⁺ ions, the Fermi level moves toward the edge of the valence band of ZnS. Photoluminescence spectra of un-doped and Cu-doped ZnS thin films was recorded under 355 nm. The emission spectrum of samples has a blue emission band at 436 nm. The peak positions of the luminescence showed a red shift as the Cu²⁺ ion concentration was increased, which indicates that the acceptor level (of Cu²⁺) is getting close to the valence band of ZnS.

Key words: ZnS, Cu²⁺ doped ZnS, UV-visible absorption, photoluminescence

References

[1]	Jindal Z, Verma N K. Effect of UV radiation on the photoluminescent properties of Cu-doped ZnS nanoparticles. Optoelectronics and Advanced Materials- Rapid Communications, 2008, 2(3): 166
[2]	Wanjari L, Bisen D P, Brahme N, et al. Thermoluminescence characteristics of ZnS:Cu nanoposphors. J Optoelectron Biomed Mater, 2015, 7(3): 59 http://www.chalcogen.ro/59_Wanjari.pdf
[3]	Linares P G, Marti A, Antolın E, et al. Voltage recovery in intermediate band solar cells. Solar Energy Materials & Solar Cells, 2012, 98: 240 http://cn.bing.com/academic/profile?id=2146240641&encoded=0&v=paper_preview&mkt=zh-cn
[4]	Puksec J D. Recombination processes and holes and electrons lifetimes. Automatika, 2002, 43: 1
[5]	Chen Jinhuo, Li Wenjian. Significant improvement of ZnS film electrical and optical performance by indium incorporation. Journal of Semiconductors, 2014, 35(9): 093003 doi: 10.1088/1674-4926/35/9/093003
[6]	Prabu H J, Johnson I, Greener C. Chemical synthesis and characterization of Mg doped ZnS nanoparticles and their engineering band gap performance. J Engineering Research and Applications, 2015, 5(8): 99 http://www.ijera.com/papers/Vol5_issue8/Part%20-%204/M580499105.pdf
[7]	Srivastava R K, Pandey N, Mishra S. Effect of Cu concentration on the photoconductivity properties of ZnS nanoparticles synthesized by co-precipitation method. Materials Science in Semiconductor Processing, 2013, 16: 1659 doi: 10.1016/j.mssp.2013.06.009
[8]	Joseph B, Manoj P K, Vaidyah V K. Studies on the structural, electrical and optical properties of Al-doped ZnO thin films prepared by chemical spray deposition. J Ceramics International, 2006, 32(5): 487 doi: 10.1016/j.ceramint.2005.03.029
[9]	Hasanzadeh J, Taherkhani A, Ghorbani M. Luminescence and structural properties of ZnS:Cu nanocrystals prepared using a wet chemical technique. Chinese Journal of Physics, 2013, 51(3): 540 http://cn.bing.com/academic/profile?id=2185201046&encoded=0&v=paper_preview&mkt=zh-cn
[10]	Long B, Cheng S, Zhou H, et al. The optical and electrical characteristics of ZnS:In thin films prepared by chemical bath deposition method. ECS Solid State Lett, 2014, 3(11): 140 doi: 10.1149/2.0041411ssl
[11]	Yamamoto T. Co-doping method for solutions of doping problems in wide-band-gap semiconductors. Phys Stat Sol A, 2002, 193(3): 423 doi: 10.1002/(ISSN)1521-396X
[12]	Li Wenjian, Chen Jinhuo, Chen Shuying. Substrate temperature effects on the structural and photoelectric properties of ZnS:In films. Journal of Semiconductors, 2014, 35(2): 023001 doi: 10.1088/1674-4926/35/2/023001
[13]	Bol A A, Ferwerda J, Bergwerf J A, et al. Luminescence of nanocrystalline ZnS:Cu²⁺. J Lumin, 2002, 99: 325 doi: 10.1016/S0022-2313(02)00350-2
[14]	Benyahia K, Benhaya A, Aida M S. ZnS thin films deposition by thermal evaporation for photovoltaic applications. Journal of Semiconductors, 2015, 36(10): 103001 doi: 10.1088/1674-4926/36/10/103001

Fig. 1. Left: Generation and recombination processes in semiconductors, (a) excitation, (b) band-band emission, (c) recombination of a free electron with a trapped hole, (d) recombination of a trapped electron with a free hole, and (e) donor-acceptor pair emission. Right: Band diagram of an IB structure showing the VB, IB and CB along with three separate quasi Fermi levels. Photons of energies above each of the sub-band gaps (E_g, E_H and E_L) pump electrons through each of the three possible transitions.

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Fig. 2. (Color online) Photograph of prepared anionic and cationic solutions with different copper concentrations.

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Fig. 3. FESEM images of (a) un-doped ZnS, (b) 0.5% Cu-doped ZnS, (c) 1% Cu-doped ZnS, (d) 2% Cu-doped ZnS, (e) 5% Cu-doped ZnS, and (f) 10% Cu-doped ZnS nanoparticles. Scale bar: 500 nm.

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Fig. 4. (Color online) X-ray diffraction patterns of ZnS and ZnS:Cu (0.5%, 1%, 2%, 5% and 10%) nanocrystals.

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Fig. 5. UV-Vis spectra of (a) un-doped ZnS, (b) 0.5% Cu-doped ZnS, (c) 1% Cu-doped ZnS, (d) 2% Cu-doped ZnS, (e) 5% Cu-doped ZnS, and (f) 10% Cu-doped ZnS nanoparticles.

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Fig. 6. Schematic energy-level diagram of (a) introduced energy level position for un-doped and different concentration of Cu-doped ZnS nanoparticles, (b) the Fermi level moves toward the edge of VB with increasing the concentration of Cu²⁺ ions.

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Fig. 7. Resistivity of the ZnS thin films with Cu²⁺ concentrations (a) 0, (b) 0.5%, (c) 1%, (d) 2%, (e) 5%, and (f) 10%.

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Fig. 8. Photoluminescence spectra of the ZnS films having different concentrations of Cu²⁺ in the range of (a) 320-400 nm and (b) 380-630 nm.

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Table 1. Electrical resistivity variation with Cu concentration.

[1]	Jindal Z, Verma N K. Effect of UV radiation on the photoluminescent properties of Cu-doped ZnS nanoparticles. Optoelectronics and Advanced Materials- Rapid Communications, 2008, 2(3): 166
[2]	Wanjari L, Bisen D P, Brahme N, et al. Thermoluminescence characteristics of ZnS:Cu nanoposphors. J Optoelectron Biomed Mater, 2015, 7(3): 59 http://www.chalcogen.ro/59_Wanjari.pdf
[3]	Linares P G, Marti A, Antolın E, et al. Voltage recovery in intermediate band solar cells. Solar Energy Materials & Solar Cells, 2012, 98: 240 http://cn.bing.com/academic/profile?id=2146240641&encoded=0&v=paper_preview&mkt=zh-cn
[4]	Puksec J D. Recombination processes and holes and electrons lifetimes. Automatika, 2002, 43: 1
[5]	Chen Jinhuo, Li Wenjian. Significant improvement of ZnS film electrical and optical performance by indium incorporation. Journal of Semiconductors, 2014, 35(9): 093003 doi: 10.1088/1674-4926/35/9/093003
[6]	Prabu H J, Johnson I, Greener C. Chemical synthesis and characterization of Mg doped ZnS nanoparticles and their engineering band gap performance. J Engineering Research and Applications, 2015, 5(8): 99 http://www.ijera.com/papers/Vol5_issue8/Part%20-%204/M580499105.pdf
[7]	Srivastava R K, Pandey N, Mishra S. Effect of Cu concentration on the photoconductivity properties of ZnS nanoparticles synthesized by co-precipitation method. Materials Science in Semiconductor Processing, 2013, 16: 1659 doi: 10.1016/j.mssp.2013.06.009
[8]	Joseph B, Manoj P K, Vaidyah V K. Studies on the structural, electrical and optical properties of Al-doped ZnO thin films prepared by chemical spray deposition. J Ceramics International, 2006, 32(5): 487 doi: 10.1016/j.ceramint.2005.03.029
[9]	Hasanzadeh J, Taherkhani A, Ghorbani M. Luminescence and structural properties of ZnS:Cu nanocrystals prepared using a wet chemical technique. Chinese Journal of Physics, 2013, 51(3): 540 http://cn.bing.com/academic/profile?id=2185201046&encoded=0&v=paper_preview&mkt=zh-cn
[10]	Long B, Cheng S, Zhou H, et al. The optical and electrical characteristics of ZnS:In thin films prepared by chemical bath deposition method. ECS Solid State Lett, 2014, 3(11): 140 doi: 10.1149/2.0041411ssl
[11]	Yamamoto T. Co-doping method for solutions of doping problems in wide-band-gap semiconductors. Phys Stat Sol A, 2002, 193(3): 423 doi: 10.1002/(ISSN)1521-396X
[12]	Li Wenjian, Chen Jinhuo, Chen Shuying. Substrate temperature effects on the structural and photoelectric properties of ZnS:In films. Journal of Semiconductors, 2014, 35(2): 023001 doi: 10.1088/1674-4926/35/2/023001
[13]	Bol A A, Ferwerda J, Bergwerf J A, et al. Luminescence of nanocrystalline ZnS:Cu²⁺. J Lumin, 2002, 99: 325 doi: 10.1016/S0022-2313(02)00350-2
[14]	Benyahia K, Benhaya A, Aida M S. ZnS thin films deposition by thermal evaporation for photovoltaic applications. Journal of Semiconductors, 2015, 36(10): 103001 doi: 10.1088/1674-4926/36/10/103001

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Received: 15 March 2016 Revised: 09 May 2016 Online: Published: 01 October 2016

Un-doped and Cu-doped ZnS (ZnS:Cu) thin films were synthesized by Successive Ion Layer Absorption and Reaction (SILAR) method. The UV-visible absorption studies have been used to calculate the band gap values of the fabricated ZnS:Cu thin films. It was observed that by increasing the concentration of Cu²⁺ ions, the Fermi level moves toward the edge of the valence band of ZnS. Photoluminescence spectra of un-doped and Cu-doped ZnS thin films was recorded under 355 nm. The emission spectrum of samples has a blue emission band at 436 nm. The peak positions of the luminescence showed a red shift as the Cu²⁺ ion concentration was increased, which indicates that the acceptor level (of Cu²⁺) is getting close to the valence band of ZnS.

Optical and electrical properties of copper-incorporated ZnS films applicable as solar cell absorbers

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