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CdZnO coated film: A material for photovoltaic applications
Results in Physics 9 (2018) 1673–1676
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
CdZnO coated film: A material for photovoltaic applications R.A. Zargar a,⇑, M.A. Bhat a, H.A. Reshi a, S.D. Khan b a b
Department of Physics, Islamic University of Science & Technology, Awantipora, Kashmir 192122, India Department of Electronics, Government Degree College (Bemina), Srinagar 192018, India
a r t i c l e
i n f o
Article history: Received 6 January 2018 Received in revised form 11 February 2018 Accepted 12 February 2018 Available online 16 February 2018 Keywords: Screen printing Structural Diffused reflectance spectroscopy and PL study
a b s t r a c t The present study reports structural and optical parameters of wide band gap oxide thick film prepared by screen-printing followed by sintering route. Characterization of the samples was carried out with UVspectroscopy, XRD, SEM, and Photoluminous study. The XRD and SEM studies reveal that the film deposited is polycrystalline, double phase, and porous with unsymmetrical grain distributions. Optical diffused reflection spectroscopy and Pl measurements give optical band gap of 2.87 eV and near band edge emission at 430 nm. Ó 2018 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction Cadmium oxide (CdO) with band gap (Eg 2.3 eV), low resistivity and optical transmittance in the visible region of the solar spectrum [1]. In comparison to Zinc oxide (ZnO) having band gap (Eg 3.36 eV) with a large exciton binding energy of 60 meV and high resistivity [2]. Since both belongs to n-type semiconductor but it is reported that to obtain simultaneously a high transmission coefficient in the visible region and good conductivity qualities is difficult [3]. However a ternary compound which combines these properties in a controlled way may allow the optimization of the window layer, for this ratio of Cd and Zn actions becomes important for obtaining a TCO film [4]. A various techniques have been reported for the preparation of CdO-ZnO alloy films such as dual ion beam sputtering deposition [5], molecular beam epitaxy [6], sol-gel process [7,8], spray pyrolysis [9] and screen printing [10]. Among these methods, screen printing is a fast- emerging, multifaceted method known for its uniformity, reproducibility and feasibility of producing cheap large-area films. It was reported in literature that Cd0.75Zn0.25O composition enhances the band gap of CdO and can be extended to green region with longer wavelength by alloying it with higher Cd. [11,12]. Therefore this study focused on the deposition of CdxZnx1O films for X = 0.75, is promising material for potential visible light optoelectronic applications, such as violet light emitting diodes and laser diodes, photo detectors, etc [13,14].
⇑ Corresponding author. E-mail address: [email protected] (R.A. Zargar).
In the present work authors synthesized the screen printed Cd0.75Zn0.25O films and investigate the structural and optical properties of the films to employ this material for the fabrication of photovoltaic devices. Characterization techniques used X-ray diffraction pattern was recorded on advanced Rigaku diffractrometer in the 2h range of 200–600 using Cu-K-X-ray radiation source. The surface morphological information was derived by using scanning electron microscope (SEM, Leo-440, UK) for recording micrographs. The optical reflection spectrum was measured on Hitachi make UV–VIS Spectrometer-3900 in the 400–700 nm range. PL spectra in 350–700 nm region have been scanned on Perkin Elmer LLS PL spectrometer at 325 nm excitation wavelength at room temperature. Taylor Hobson (Taly step UK) instrument has been used for film thickness measurement and thickness of the film is found to be 5lm. Preparation of Cd0.75Zn0.25O composition for coating The molecular weight of CdO = 128.4104. & Molecular weight of ZnO = 81.408 Hence the calculated amounts of Cd0.75 Zn0.25O compositions are Weight of CdO = 128.4104 0.75 = 96.3078 gm And weight of ZnO = 81.408 0.25 = 20.352 gm And weight of CdCl2 = 10/100 116.659 = 11.67 gm
https://doi.org/10.1016/j.rinp.2018.02.027 2211-3797/Ó 2018 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
The above calculation is very large so we reduce all the weights same preposition. All the above three were mix properly and a paste was prepared with ethylene Glycole, the paste thus prepared was screen printed on various glass substrates. The film thus prepared dried at 120 °C for 2 h than at higher temperature 500 °C for 10 min in an air atmosphere [15]. The steps involved in the preparation of Cd0.75Zn0.25O composition thick films by screen printing method as described above are presented in the following schematic flow chart as shown if (Fig. 1) [16]. Results and discussions Structure analysis XRD patterns of the Cd0.075Zn0.25O composite coated films deposited onto the glass substrate and are shown in (Fig. 2). A combination of cubic CdO and hexagonal wurtzite ZnO phases was observed. The polycrystalline CdO peaks in the patterns were identified as (1 1 1), (2 0 0), (2 2 0) and (3 1 1), while those of ZnO were indexed as (1 0 0), (0 0 2) and (1 0 1), respectively. These peaks are in agreement with the standard values of JCPDS (05-0640) for CdO [10] and JCPDS (36-1451) for ZnO [16]. The mean crystallite size (D) was evaluated according to broadening of the highest intensity peak corresponding to the (1 1 1) diffraction plane using the Debye-Scherrer formula shown in Eq. (1) [17]:
D¼
0:94k bCosh
ð1Þ
where k, b, and h are the X-ray wavelength (1.5418 Å), full width at half maximum (FWHM) in radians and from this formula the D was found to be 38.29 nm. The dislocation density (d) was calculated from D using Eq. (2) [17]:
d¼
1
ð2Þ
D2
this was found to be 0.6821 103 (nm)2 and the Strain present in the film calculated from Eq. (3) is found to be 094.51 105 [13]:
e¼
b cos h 4
ð3Þ
Fig. 1. Screen Printing procedure diagram.
Fig. 2. XRD of Cd0.75Zn0.25O thick film.
This lower value for d implied that our films had very few lattice defects and good crystalline qualities and these values are in good agreement [18]. Scanning electron microscopy (SEM) analysis The surface morphology of Cd0.075Zn0.25O composite coated films were studied by scanning electron microscopy (SEM). The presence of some residual, intragranular porosity and agglomeration of grains at some region are shown in the (Fig. 3). The hexagonal and cubic tipped rods confirm the co-existence of ZnO Wurtzite and CdO cuboidal morphologies respectively with dominating Zn-doped CdO structure, hence such structures are useful for sensing and semiconducting devices.
Optical properties UV–vis Diffused reflectance (UV-DR) and photoluminescence (PL) studies, performed at room temperature (RT), have been employed to know the optical properties of the Cd0.075Zn0.25O composite. Diffuse reflectance spectra of the sample are shown in
Fig. 3. SEM image of Cd0.75Zn0.25O thick film.
R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
1675
Fig. 6. PL emission spectra for Cd0.75Zn0.25O thick film. Fig. 4. Reflection spectra of Cd0.75Zn0.25O thick film.
(Fig. 4) and the optical absorption coefficient (a) was calculated from the Eq. (4) with Kubelka–Munk treatment [19]:
a¼
FðRÞ t
ð4Þ
Where t and R are the film thickness and reflectance respectively. The intersection between the linear fit and the photon energy axis gives the value of energy band gap (Eg). The calculated band gap comes out to be 2.87 eV and has shown in (Fig. 5). Hence, the band gap energy of Cd0.075Zn0.25O composite is highly blue shifted with higher CdO content compared to that of CdO [16]. The blue shift in the emission peak could be attributed to the existence of cubic and hexagonal phases at the interface of the composite. The movement of the absorption edge to the shorter wavelength region is the Burstein–Moss shift, which is due to the increase of carrier concentration.
Room temperature photoluminescence (PL) spectra were recorded to study the optical emission characteristic of prepared Cd0.75Zn0.25O composite shown in (Fig. 6). The NBE emission peak from Cd0.75Zn0.25O composite exhibit a strong UV emission peak at 430 nm (2.88 eV) and very small shoulder occurs at 470 nm (2.63 eV) depicts band-edge transition of the CdO at higher content of CdO. This two PL emission peaks are critical in order to realize violet emission could be attribute due to the transition occurring from Zn interstitials (Zni) to the valence band. Besides the green emissions at 566 nm and 596 nm arised due to recombination of photogenerated holes by the oxygen vacancies or to the increase in the porosity of the film, that generally observed for the coated film [20,21]. Conclusion In conclusion prepared Cd0.75Zn0.25O alloy by screen printing method is cost effective reasonably accurate and efficient. The structural and optical studies of these films indicate that the films are quite suitable for photovoltaic device fabrication. The study of structural confirms both phases present and from optical study direct transition has been observed with suitable energy band gap. The PL spectra indicates that the CdZnO composite contain defects. Reports suggests that this material might be practically useful for optoelectronic devices. Acknowledgments Dr. R.A. Zargar would like to thank Prof. M. A. Siddiqi (Vice Chancellor) of IUST, Dr. A.K. Hafiz from (JMI) and Prof. F.H. Bhat (HOD) Physics, IUST for their kind full cooperation throughout this tenure. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.rinp.2018.02.027. References
Fig. 5. Variation of [ahv)]2 versus hv for Cd0.75Zn0.25O thick film.
[1] Lanje AS, Ningthoujam RS, Sharma SJ, Pode RB. Indian J. Pure Appl. Phys. 2011;49:234. [2] Mosquera E, Pozo ID, Morel M. J. Solid State Chem. 2013;206:265. [3] Chopra KL, Major S, Pandya DK. Thin Solid Films 1983;102:1.
1676 [4] [5] [6] [7] [8] [9] [10]
R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
Abdoladeh A, Ziabari F, Ghodsi E. J. Alloys Comp. 2011;509:8748. Pandey SK, Awasthi V, Verma S, Mukherjee S. Opt. Exp. 2014;22(30983):30983. Yan M, Lane M, Kannewurf CR, Chang RPH. Appl. Phys. Lett. 2001;78:2342. Cruz JS, Delgado GT, Perez RC, et al. Thin Solid Films 2005;493:83. Subramanyam TK, Uthanna S, Naidu BS. Mater. Lett. 1998;35:214. Liu X, Li C, Han S, Han J, Zhou C. Appl. Phys. Lett. 2003;82:1950. Zargar RA, Chackrabarti S, Shahabuddin Md, Kumar J, Arora M, Hafiz AK. J. Mater. Sci.: Mater. Electron. 2015;26:10027. [11] Ohtomo A et al. Appl. Phys. Lett. 1999;72:2466. [12] Shigemori S, Nakamura A, Ishihara J, Aoki T, Temmyo J. Jpn. J. Appl. Phys. 2004; Part 2(43):1088.
[13] Caglar Y, Caglar M, Ilican S, Ates A. J. Phys. D: Appl. Phys. 2009;42:065421. [14] Samanta PK, Chaudhuri PR. Sci. Adv. Mater. 2011;3:112. [15] Zargar RA, Chackrabarti S, Joseph S, Khan MS, Hussain R, Hafiz AK. Optik 2015;126:4171. [16] Zargar RA, Chackrabarti S, Arora M, Hafiz AK. Int. Nano Lett. 2016;2(6):104. [17] Warren BE. X-ray Diffraction. New-York: Dover; 1990. p. 253. [18] Singh A, Kumar P. Int. Nano Lett. 2013;3:57. [19] Zargar RA, Bhat MA, Parrey IR, Kumar J, Arora M, Hafiz AK. Optik 2016;127:6997. [20] Fang Z, Wang Y, Xu D, Tan Y, Liu X. Opt. Mater. 2004;26:242. [21] Ghodsi FE, Absalan H. Acta Phys Pol. A 2010;118(4):659.
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
CdZnO coated film: A material for photovoltaic applications R.A. Zargar a,⇑, M.A. Bhat a, H.A. Reshi a, S.D. Khan b a b
Department of Physics, Islamic University of Science & Technology, Awantipora, Kashmir 192122, India Department of Electronics, Government Degree College (Bemina), Srinagar 192018, India
a r t i c l e
i n f o
Article history: Received 6 January 2018 Received in revised form 11 February 2018 Accepted 12 February 2018 Available online 16 February 2018 Keywords: Screen printing Structural Diffused reflectance spectroscopy and PL study
a b s t r a c t The present study reports structural and optical parameters of wide band gap oxide thick film prepared by screen-printing followed by sintering route. Characterization of the samples was carried out with UVspectroscopy, XRD, SEM, and Photoluminous study. The XRD and SEM studies reveal that the film deposited is polycrystalline, double phase, and porous with unsymmetrical grain distributions. Optical diffused reflection spectroscopy and Pl measurements give optical band gap of 2.87 eV and near band edge emission at 430 nm. Ó 2018 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction Cadmium oxide (CdO) with band gap (Eg 2.3 eV), low resistivity and optical transmittance in the visible region of the solar spectrum [1]. In comparison to Zinc oxide (ZnO) having band gap (Eg 3.36 eV) with a large exciton binding energy of 60 meV and high resistivity [2]. Since both belongs to n-type semiconductor but it is reported that to obtain simultaneously a high transmission coefficient in the visible region and good conductivity qualities is difficult [3]. However a ternary compound which combines these properties in a controlled way may allow the optimization of the window layer, for this ratio of Cd and Zn actions becomes important for obtaining a TCO film [4]. A various techniques have been reported for the preparation of CdO-ZnO alloy films such as dual ion beam sputtering deposition [5], molecular beam epitaxy [6], sol-gel process [7,8], spray pyrolysis [9] and screen printing [10]. Among these methods, screen printing is a fast- emerging, multifaceted method known for its uniformity, reproducibility and feasibility of producing cheap large-area films. It was reported in literature that Cd0.75Zn0.25O composition enhances the band gap of CdO and can be extended to green region with longer wavelength by alloying it with higher Cd. [11,12]. Therefore this study focused on the deposition of CdxZnx1O films for X = 0.75, is promising material for potential visible light optoelectronic applications, such as violet light emitting diodes and laser diodes, photo detectors, etc [13,14].
⇑ Corresponding author. E-mail address: [email protected] (R.A. Zargar).
In the present work authors synthesized the screen printed Cd0.75Zn0.25O films and investigate the structural and optical properties of the films to employ this material for the fabrication of photovoltaic devices. Characterization techniques used X-ray diffraction pattern was recorded on advanced Rigaku diffractrometer in the 2h range of 200–600 using Cu-K-X-ray radiation source. The surface morphological information was derived by using scanning electron microscope (SEM, Leo-440, UK) for recording micrographs. The optical reflection spectrum was measured on Hitachi make UV–VIS Spectrometer-3900 in the 400–700 nm range. PL spectra in 350–700 nm region have been scanned on Perkin Elmer LLS PL spectrometer at 325 nm excitation wavelength at room temperature. Taylor Hobson (Taly step UK) instrument has been used for film thickness measurement and thickness of the film is found to be 5lm. Preparation of Cd0.75Zn0.25O composition for coating The molecular weight of CdO = 128.4104. & Molecular weight of ZnO = 81.408 Hence the calculated amounts of Cd0.75 Zn0.25O compositions are Weight of CdO = 128.4104 0.75 = 96.3078 gm And weight of ZnO = 81.408 0.25 = 20.352 gm And weight of CdCl2 = 10/100 116.659 = 11.67 gm
https://doi.org/10.1016/j.rinp.2018.02.027 2211-3797/Ó 2018 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1674
R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
The above calculation is very large so we reduce all the weights same preposition. All the above three were mix properly and a paste was prepared with ethylene Glycole, the paste thus prepared was screen printed on various glass substrates. The film thus prepared dried at 120 °C for 2 h than at higher temperature 500 °C for 10 min in an air atmosphere [15]. The steps involved in the preparation of Cd0.75Zn0.25O composition thick films by screen printing method as described above are presented in the following schematic flow chart as shown if (Fig. 1) [16]. Results and discussions Structure analysis XRD patterns of the Cd0.075Zn0.25O composite coated films deposited onto the glass substrate and are shown in (Fig. 2). A combination of cubic CdO and hexagonal wurtzite ZnO phases was observed. The polycrystalline CdO peaks in the patterns were identified as (1 1 1), (2 0 0), (2 2 0) and (3 1 1), while those of ZnO were indexed as (1 0 0), (0 0 2) and (1 0 1), respectively. These peaks are in agreement with the standard values of JCPDS (05-0640) for CdO [10] and JCPDS (36-1451) for ZnO [16]. The mean crystallite size (D) was evaluated according to broadening of the highest intensity peak corresponding to the (1 1 1) diffraction plane using the Debye-Scherrer formula shown in Eq. (1) [17]:
D¼
0:94k bCosh
ð1Þ
where k, b, and h are the X-ray wavelength (1.5418 Å), full width at half maximum (FWHM) in radians and from this formula the D was found to be 38.29 nm. The dislocation density (d) was calculated from D using Eq. (2) [17]:
d¼
1
ð2Þ
D2
this was found to be 0.6821 103 (nm)2 and the Strain present in the film calculated from Eq. (3) is found to be 094.51 105 [13]:
e¼
b cos h 4
ð3Þ
Fig. 1. Screen Printing procedure diagram.
Fig. 2. XRD of Cd0.75Zn0.25O thick film.
This lower value for d implied that our films had very few lattice defects and good crystalline qualities and these values are in good agreement [18]. Scanning electron microscopy (SEM) analysis The surface morphology of Cd0.075Zn0.25O composite coated films were studied by scanning electron microscopy (SEM). The presence of some residual, intragranular porosity and agglomeration of grains at some region are shown in the (Fig. 3). The hexagonal and cubic tipped rods confirm the co-existence of ZnO Wurtzite and CdO cuboidal morphologies respectively with dominating Zn-doped CdO structure, hence such structures are useful for sensing and semiconducting devices.
Optical properties UV–vis Diffused reflectance (UV-DR) and photoluminescence (PL) studies, performed at room temperature (RT), have been employed to know the optical properties of the Cd0.075Zn0.25O composite. Diffuse reflectance spectra of the sample are shown in
Fig. 3. SEM image of Cd0.75Zn0.25O thick film.
R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
1675
Fig. 6. PL emission spectra for Cd0.75Zn0.25O thick film. Fig. 4. Reflection spectra of Cd0.75Zn0.25O thick film.
(Fig. 4) and the optical absorption coefficient (a) was calculated from the Eq. (4) with Kubelka–Munk treatment [19]:
a¼
FðRÞ t
ð4Þ
Where t and R are the film thickness and reflectance respectively. The intersection between the linear fit and the photon energy axis gives the value of energy band gap (Eg). The calculated band gap comes out to be 2.87 eV and has shown in (Fig. 5). Hence, the band gap energy of Cd0.075Zn0.25O composite is highly blue shifted with higher CdO content compared to that of CdO [16]. The blue shift in the emission peak could be attributed to the existence of cubic and hexagonal phases at the interface of the composite. The movement of the absorption edge to the shorter wavelength region is the Burstein–Moss shift, which is due to the increase of carrier concentration.
Room temperature photoluminescence (PL) spectra were recorded to study the optical emission characteristic of prepared Cd0.75Zn0.25O composite shown in (Fig. 6). The NBE emission peak from Cd0.75Zn0.25O composite exhibit a strong UV emission peak at 430 nm (2.88 eV) and very small shoulder occurs at 470 nm (2.63 eV) depicts band-edge transition of the CdO at higher content of CdO. This two PL emission peaks are critical in order to realize violet emission could be attribute due to the transition occurring from Zn interstitials (Zni) to the valence band. Besides the green emissions at 566 nm and 596 nm arised due to recombination of photogenerated holes by the oxygen vacancies or to the increase in the porosity of the film, that generally observed for the coated film [20,21]. Conclusion In conclusion prepared Cd0.75Zn0.25O alloy by screen printing method is cost effective reasonably accurate and efficient. The structural and optical studies of these films indicate that the films are quite suitable for photovoltaic device fabrication. The study of structural confirms both phases present and from optical study direct transition has been observed with suitable energy band gap. The PL spectra indicates that the CdZnO composite contain defects. Reports suggests that this material might be practically useful for optoelectronic devices. Acknowledgments Dr. R.A. Zargar would like to thank Prof. M. A. Siddiqi (Vice Chancellor) of IUST, Dr. A.K. Hafiz from (JMI) and Prof. F.H. Bhat (HOD) Physics, IUST for their kind full cooperation throughout this tenure. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.rinp.2018.02.027. References
Fig. 5. Variation of [ahv)]2 versus hv for Cd0.75Zn0.25O thick film.
[1] Lanje AS, Ningthoujam RS, Sharma SJ, Pode RB. Indian J. Pure Appl. Phys. 2011;49:234. [2] Mosquera E, Pozo ID, Morel M. J. Solid State Chem. 2013;206:265. [3] Chopra KL, Major S, Pandya DK. Thin Solid Films 1983;102:1.
1676 [4] [5] [6] [7] [8] [9] [10]
R.A. Zargar et al. / Results in Physics 9 (2018) 1673–1676
Abdoladeh A, Ziabari F, Ghodsi E. J. Alloys Comp. 2011;509:8748. Pandey SK, Awasthi V, Verma S, Mukherjee S. Opt. Exp. 2014;22(30983):30983. Yan M, Lane M, Kannewurf CR, Chang RPH. Appl. Phys. Lett. 2001;78:2342. Cruz JS, Delgado GT, Perez RC, et al. Thin Solid Films 2005;493:83. Subramanyam TK, Uthanna S, Naidu BS. Mater. Lett. 1998;35:214. Liu X, Li C, Han S, Han J, Zhou C. Appl. Phys. Lett. 2003;82:1950. Zargar RA, Chackrabarti S, Shahabuddin Md, Kumar J, Arora M, Hafiz AK. J. Mater. Sci.: Mater. Electron. 2015;26:10027. [11] Ohtomo A et al. Appl. Phys. Lett. 1999;72:2466. [12] Shigemori S, Nakamura A, Ishihara J, Aoki T, Temmyo J. Jpn. J. Appl. Phys. 2004; Part 2(43):1088.
[13] Caglar Y, Caglar M, Ilican S, Ates A. J. Phys. D: Appl. Phys. 2009;42:065421. [14] Samanta PK, Chaudhuri PR. Sci. Adv. Mater. 2011;3:112. [15] Zargar RA, Chackrabarti S, Joseph S, Khan MS, Hussain R, Hafiz AK. Optik 2015;126:4171. [16] Zargar RA, Chackrabarti S, Arora M, Hafiz AK. Int. Nano Lett. 2016;2(6):104. [17] Warren BE. X-ray Diffraction. New-York: Dover; 1990. p. 253. [18] Singh A, Kumar P. Int. Nano Lett. 2013;3:57. [19] Zargar RA, Bhat MA, Parrey IR, Kumar J, Arora M, Hafiz AK. Optik 2016;127:6997. [20] Fang Z, Wang Y, Xu D, Tan Y, Liu X. Opt. Mater. 2004;26:242. [21] Ghodsi FE, Absalan H. Acta Phys Pol. A 2010;118(4):659.