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Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents
Author's Accepted Manuscript
Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents Mehdi Mousavi-Kamazani, Masoud SalavatiNiasari, Mohammad Sadeghinia
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)02180-6 http://dx.doi.org/10.1016/j.matlet.2014.12.014 MLBLUE18165
To appear in:
Materials Letters
Received date: 19 November 2014 Accepted date: 2 December 2014 Cite this article as: Mehdi Mousavi-Kamazani, Masoud Salavati-Niasari, Mohammad Sadeghinia, Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2014.12.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents Mehdi Mousavi-Kamazani, MasoudSalavati-Niasari*, Mohammad Sadeghinia Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 87317-51167, I. R. Iran. *Corresponding author: Tel.: +98 361 5555 333, Fax: +98 361 555 29 30. E-mail address: [email protected] (MasoudSalavati-Niasari)
Abstract
CuInS2 (CIS) nanoparticles were synthesized through a simple hydrothermal method using
pomegranate marc peel (PMP) dyes-Cu(II) as a new copper precursor and sodium sulfite (Na2SO3) as a reducing agent. The PMP has several dyes such as proanthocyanidins and flavonoids which can be easily extracted by transition metal ions in which we have focused on this work to prepare of copper precursor and dye solar cells. Besides, the effect of HCl on the morphology and particle size of the product was investigated. Furthermore, to investigate the effect of different dyes and CIS nanoparticles on solar cell efficiencies several experiments were conducted. Keywords: CuInS2; Nanoparticles; Solar energy materials; Electron microscopy; Natural dye.
1.
Introduction
The chalcopyrite semiconductor CuInS2 (CIS) is particularly promising for photovoltaic applications due to its layer absorption coefficient of about 105 cm-1 and a direct band gap energy of approximately 1.54 eV which is in the optimum range for solar-energy conversion [1]. During recent years great attempts were performed to synthesis of this material and many procedures such as solvothermal, polyol and etc have been employed to prepare it [1]. To our knowledge, there is not much report about hydrothermal synthesis of mentioned
1
nanoparticles. Because selecting a convenient reducing agent to reduce the Cu2+ to Cu+ is faced restriction. Generally polyol solvents including ethylene glycol, propylene glycol and etc are used to synthesis because these solvents are able to reduce the Cu2+ to Cu+ at elevated temperatures. Nevertheless, these solvents are expensive and working with them is more difficult than water. Here we reported a simple hydrothermal route in which new PMP dyes-Cu(II) reagents as a copper source and sodium sulfite as a reducing agent were utilized to synthesis CIS nanoparticles. It has been proved that pomegranate peel is a rich source of different pigments such as phenolics, proanthocyanidins and flavonoids which are easily extracted. Since the ruthenium dyes such as N719 are expensive and toxic, natural dyes have attracted much attention during recent years. However, mildew and rot and subsequently their low persistence are challenging issues with the natural dyes. One of the most common approaches to overcome this problem is to convert the fruit essence to the powder. This procedure is time cost and expensive. Another method we have dealt with here is separating the pigments by complex formation with metallic ions. So we extracted the pomegranate peel pigments by Cu2+ ions. Moreover high persistency of prepared PMP dyes-Cu(II) complex, this complex can be used in single step in FTO/TiO2/CIS/dye three layered solar cells. These kinds of solar cells due to formation of barrier layer by CIS, has higher conversion than pure dye or CIS [2]. 2. Experimental Materials and characterization: All the chemical reagents were of analytical grade and were used as received without any further purification. The Pomegranate marc Peels (PMP) were collected and washed thoroughly with water to remove any impurities. After drying at room temperature, the samples were ground into powder by means of grinder. In order to synthesis of FTO/TiO2 and FTO/TiO2/CIS/Pt-FTO the same procedure similar to our previous method was selected [3]. Fourier transform infrared (FT-IR) spectra were recorded on Magna-IR, spectrometer 550 Nicolet with 0.125 cm-1 resolution in KBr pellets in the range of 400-4000 cm-1. X-ray diffraction (XRD) patterns were recorded by a Philips-X’PertPro, X-ray diffractometer using Ni-filtered Cu Kα
2
radiation at scan range of 10<2θ<80. Scanning electron microscopy (SEM) images were obtained on LEO1455VP equipped with an energy dispersive X-ray spectroscopy. Transmission electron microscope (TEM) images were obtained on a Philips Zeiss-EM10C transmission electron microscope with an accelerating voltage of 80 kV. Photocurrentdensity-voltage (J-V) curve was measured by using computerized digital multimeters (Ivium-n-Stat Multichannel potentiostat) and a variable load. A 300 W metal xenon lamp (Luzchem) served as asimulated sun light source, and its light intensity (or radiant power) was adjusted to simulated AM 1.5 radiation at 100 mW/cm2 with a filters for this purpose. PMP dyes-Cu(II) complex preparation: 2 gr of dried and powdered pomegranate peel was dissolved in 30 ml water under middle stirring for 30 minutes followed the prepared solution was filtered. 0.2 gr CuSO4.5H2O dissolved in 10 ml water was added to the filtered solution and stirred for 2 h at 60 °C. After thermal treatment, the system was maintained to cool down to room temperature and the resulting precipitates were collected. Finally, it was washed with distilled water and dried at 80 °C for 10 h. CIS synthesis: Prepared PMP dyes-Cu(II) complex and 0.15 gr InCl3 were suspended into 30 ml distilled water under stirring. After 10 min, 0.1 gr Na2SO3 and 3ml HCl (40%) were introduced to the mixture and after 5 min 0.1 gr TAA was added and the final solution was transferred to the autoclave maintained at 190 °C for 10 h (sample 1). The same experiment without HCl was performed to investigate the effect of HCl (sample 2). Fabrication of FTO/TiO2/CIS/PMP dyes/Pt-FTO: After cooling down to room temperature, the solution was transferred to a beaker under vigorous stirring for 5 minutes. After that, FTO/TiO2 was maintained for 10 h in the beaker. In this way, prepared nanoparticles together with dye were deposited on FTO/TiO2 film. Prepared FTO/TiO2/CIS/dye was washed with a little amount of water. Then counter-electrode was made from deposition of a Pt solution on FTO glass. Afterwards, this electrode was placed over FTO/TiO2/CIS/dye electrode [3].
3
3. Results and discussion The XRD results for samples 1 and 2 presented in Fig. 1 (a and b respectively) show broadened lines, which were assigned to tetragonal phase of CuInS2 (a = b = 5.5200 Å, and c = 11.1200Å) with space group of I-42d and JCPDS No. 38–0777.
Fig. 1. XRD patterns of a: sample 1 and b: sample 2.
No diffraction peaks relating to other species in Fig. 1a could be detected indicating that the obtained sample in the presence of HCl (sample 1) is pure, while XRD pattern of sample obtained without HCl (sample 2) revealed the presence of some impurity such as CuS and Cu2S in the final product which in turn confirms the fact that HCl is necessary for obtaining CuInS2 nanoparticles. Figs. 2a-d illustrate the SEM and TEM images of the PMP dyesCu(II) complex and CIS samples, respectively. Fig. 2a suggests that the complex is mainly composed of a large amount of sphere-like nanoparticles. Figs. 2b and c in Presented SEM images belongs to the prepared samples in presence and absence of HCl (samples 1 and 2, respectively). As clearly seen, in both synthetic conditions nanoparticles have been formed but nanoparticles prepared in acid absence have smaller sizes. Acid introducing to the reaction media causes decreasing of sulfide ion producing and subsequently decreases nucleation rate and 4
so nanoparticles will be coarser. According to the TEM image of the CIS (sample 1, Fig. 2d), the particle size of the product is about 10-15 nm.
Fig. 2. SEM images of a: PMP dyes-Cu(II) complex, b: sample 1, c: sample 2, and d: TEM image of sample 1.
Figs. 3a and b Show the FT-IR transition spectra of PMP dyes-Cu(II) complex and CIS nanoparticles obtained at 190 °C in presence of HCl (sample 1). In these spectra, stretching and bending vibrations of O–H appeared at
5
about 3425 and 1624 cm-1, respectively. The absorption peak at 1389 cm-1 corresponds to –COOH symmetry stretching vibrations, while absorptions at 2909 and 801 cm–1 are related to stretching and bending vibrations of C–H bond, respectively [4]. Moreover, the absorption peak at 570 cm-1 is due to Cu–O bond. Finally, the band at 1025 cm-1 is related to C–C vibrations [4]. According to Fig. 3b, it is obvious that there are not important peaks indicating that there is not any organic molecule absorbed on the surface of samples. In order to compare the effect of the adsorption mode on TiO2surface on the harvesting of light over a wide range of wavelengths, several tests were performed. The photovoltaic parameters obtained by measuring J-V curves (Figs. 3c and d) are shown in Table 1. The energy conversion efficiencies of the dye-sensitized solar cells using N719, CIS NPs, PMP dyes, and CIS-PMP dyes were 3.03, 0.12, 0.19, and 0.37%, respectively. Obviously a remarkable enhancement in efficiency takes place for the mixture of dye-nanoparticles compared to the pure dye or nanoparticles. Table 1 Energy conversion efficiency of DSSCs adsorbed with a: N719, b: CIS, PMP dyes and CIS-PMP dyes.
Dyes N719 CIS
PMP dyes CIS-PMP dyes
Voc (V) 0.75 0.52 0.48 0.54
Jsc (mA/cm2) 9.7 0.365 0.771 1.05
FF 0.42 0.62 0.51 0.66
η(%) 3.03 0.12 0.19 0.37
This enhancement is the result of barrier layer formation by nanoparticles which in turn increases electron lifetime [2]. Fig. 3e shows barrier layer and energy levels diagram of TiO2/CIS/PMP dyes. As clearly seen, LUMO of CuInS2 (-4.1 eV) is energetically lower than LUMO of dye (-3.51 eV) and higher than LUMO of TiO2 (-4.2 eV) revealing that electrons can be transferred from valance band of dye and CuInS2 to the conductance band of TiO2. (The examined highest occupied molecular orbital (HOMO) levels and the lowest unoccupied molecular orbital (LUMO) levels were calculated using Guo et al [2] method). The related reaction to form stoichiometric CuInS2 during hydrothermal process might be given in Eq (5). SO32- + H2O Æ SO42- + 2H+ + 2e
Eq. (1)
2Cu2+ + 2e Æ 2Cu+
Eq. (2) 6
2Cu++ S2- Æ Cu2S
Eq. (3)
2In3+ + 3S2- Æ In2S3
Eq. (4)
Cu2S + In2S3 Æ 2CuInS2
Eq. (5)
Fig. 3. FT-IR spectra of a: PMP dyes-Cu(II) complex, b: CIS nanoparticles and photocurrent-voltage curves of DSSCs adsorbed with c: N719, d: CIS, PMP dyes and CIS-PMP dyes, e: energy diagram of the photoanode.
In comparison with similar works, the current work is easier to control and more affordable. In this study, sodium sulfite was used instead of polyol solvents as a reducing agent to reduce of Cu2+ to Cu+ and this product (CuInS2) can be easily synthesized in aqueous media. Besides, PMP dyes were extracted by Cu2+ and new copper precursor was obtained which its using has many advantages such as: no need to any surfactant, possibility of 7
single step production of three layered solar cells, presentation a comprehensive method to increase of longevity of natural dyes and etc. 4. Conclusions Concisely, to improve the efficiency of solar cells, CuInS2 nanoparticles were synthesized using PMP dyesCu(II) and Na2SO3 as the new reagents in an acidic media through hydrothermal route. Pomegranate peel was used as a copper source. X-ray diffraction analysis showed that presence of HCl is crucial to synthesis of pure CIS nanoparticles. Finally FTO/TiO2/CIS/PMP dyes/Pt-FTO solar cell was prepared by single step deposition of dye and CIS on TiO2 nanoparticles for the first time and its performance was investigated. The results indicated that simultaneous use of dye and nanoparticles due to formation of barrier layer resulted in higher efficiencies. Acknowledgment Authors are grateful to council of University of Kashan for providing financial support to undertake this work by Grant No (159271/220). References [1] Zhou J, Li S, Gong X, Yang Y, Guo Y. Preparation of CuInS2 microspheres via a facile solution–chemical method. Mater Lett 2011; 65:2001–3. [2] Guo F, He J, Li J, Wu W, Hang Y, H Jianli. Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material. J Colloid Interf Sci 2013; 408:59–65. [3] Panahi-Kalamuei M, Salavati-Niasari M, Hosseinpour-Mashkani SM. Facile microwave synthesis, characterization, and solar cell application of selenium nanoparticles. J Alloy Compd 2014; 617:627–32. [4] Mohandes F, Salavati-Niasari M. Sonochemical synthesis of silver vanadium oxide micro/nanorods: Solvent and surfactant effects. Ultrason Sonochem 2013; 20:354–65.
8
Highlights ¾ CIS nanoparticles were synthesized using new starting reagents through hydrothermal route. ¾ Pomegranate marc peels (PMP) was used to prepare of copper precursor and dye solar cells. ¾ The XRD results indicated that presence of HCl is crucial to synthesis of pure CuInS2 (CIS). ¾ FTO/TiO2/CIS/PMP dyes/Pt-FTO solar cell was prepared for the first time.
9
Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents Mehdi Mousavi-Kamazani, Masoud SalavatiNiasari, Mohammad Sadeghinia
www.elsevier.com/locate/matlet
PII: DOI: Reference:
S0167-577X(14)02180-6 http://dx.doi.org/10.1016/j.matlet.2014.12.014 MLBLUE18165
To appear in:
Materials Letters
Received date: 19 November 2014 Accepted date: 2 December 2014 Cite this article as: Mehdi Mousavi-Kamazani, Masoud Salavati-Niasari, Mohammad Sadeghinia, Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2014.12.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile hydrothermal synthesis, formation mechanism and solar cell application of CuInS2 nanoparticles using novel starting reagents Mehdi Mousavi-Kamazani, MasoudSalavati-Niasari*, Mohammad Sadeghinia Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 87317-51167, I. R. Iran. *Corresponding author: Tel.: +98 361 5555 333, Fax: +98 361 555 29 30. E-mail address: [email protected] (MasoudSalavati-Niasari)
Abstract
CuInS2 (CIS) nanoparticles were synthesized through a simple hydrothermal method using
pomegranate marc peel (PMP) dyes-Cu(II) as a new copper precursor and sodium sulfite (Na2SO3) as a reducing agent. The PMP has several dyes such as proanthocyanidins and flavonoids which can be easily extracted by transition metal ions in which we have focused on this work to prepare of copper precursor and dye solar cells. Besides, the effect of HCl on the morphology and particle size of the product was investigated. Furthermore, to investigate the effect of different dyes and CIS nanoparticles on solar cell efficiencies several experiments were conducted. Keywords: CuInS2; Nanoparticles; Solar energy materials; Electron microscopy; Natural dye.
1.
Introduction
The chalcopyrite semiconductor CuInS2 (CIS) is particularly promising for photovoltaic applications due to its layer absorption coefficient of about 105 cm-1 and a direct band gap energy of approximately 1.54 eV which is in the optimum range for solar-energy conversion [1]. During recent years great attempts were performed to synthesis of this material and many procedures such as solvothermal, polyol and etc have been employed to prepare it [1]. To our knowledge, there is not much report about hydrothermal synthesis of mentioned
1
nanoparticles. Because selecting a convenient reducing agent to reduce the Cu2+ to Cu+ is faced restriction. Generally polyol solvents including ethylene glycol, propylene glycol and etc are used to synthesis because these solvents are able to reduce the Cu2+ to Cu+ at elevated temperatures. Nevertheless, these solvents are expensive and working with them is more difficult than water. Here we reported a simple hydrothermal route in which new PMP dyes-Cu(II) reagents as a copper source and sodium sulfite as a reducing agent were utilized to synthesis CIS nanoparticles. It has been proved that pomegranate peel is a rich source of different pigments such as phenolics, proanthocyanidins and flavonoids which are easily extracted. Since the ruthenium dyes such as N719 are expensive and toxic, natural dyes have attracted much attention during recent years. However, mildew and rot and subsequently their low persistence are challenging issues with the natural dyes. One of the most common approaches to overcome this problem is to convert the fruit essence to the powder. This procedure is time cost and expensive. Another method we have dealt with here is separating the pigments by complex formation with metallic ions. So we extracted the pomegranate peel pigments by Cu2+ ions. Moreover high persistency of prepared PMP dyes-Cu(II) complex, this complex can be used in single step in FTO/TiO2/CIS/dye three layered solar cells. These kinds of solar cells due to formation of barrier layer by CIS, has higher conversion than pure dye or CIS [2]. 2. Experimental Materials and characterization: All the chemical reagents were of analytical grade and were used as received without any further purification. The Pomegranate marc Peels (PMP) were collected and washed thoroughly with water to remove any impurities. After drying at room temperature, the samples were ground into powder by means of grinder. In order to synthesis of FTO/TiO2 and FTO/TiO2/CIS/Pt-FTO the same procedure similar to our previous method was selected [3]. Fourier transform infrared (FT-IR) spectra were recorded on Magna-IR, spectrometer 550 Nicolet with 0.125 cm-1 resolution in KBr pellets in the range of 400-4000 cm-1. X-ray diffraction (XRD) patterns were recorded by a Philips-X’PertPro, X-ray diffractometer using Ni-filtered Cu Kα
2
radiation at scan range of 10<2θ<80. Scanning electron microscopy (SEM) images were obtained on LEO1455VP equipped with an energy dispersive X-ray spectroscopy. Transmission electron microscope (TEM) images were obtained on a Philips Zeiss-EM10C transmission electron microscope with an accelerating voltage of 80 kV. Photocurrentdensity-voltage (J-V) curve was measured by using computerized digital multimeters (Ivium-n-Stat Multichannel potentiostat) and a variable load. A 300 W metal xenon lamp (Luzchem) served as asimulated sun light source, and its light intensity (or radiant power) was adjusted to simulated AM 1.5 radiation at 100 mW/cm2 with a filters for this purpose. PMP dyes-Cu(II) complex preparation: 2 gr of dried and powdered pomegranate peel was dissolved in 30 ml water under middle stirring for 30 minutes followed the prepared solution was filtered. 0.2 gr CuSO4.5H2O dissolved in 10 ml water was added to the filtered solution and stirred for 2 h at 60 °C. After thermal treatment, the system was maintained to cool down to room temperature and the resulting precipitates were collected. Finally, it was washed with distilled water and dried at 80 °C for 10 h. CIS synthesis: Prepared PMP dyes-Cu(II) complex and 0.15 gr InCl3 were suspended into 30 ml distilled water under stirring. After 10 min, 0.1 gr Na2SO3 and 3ml HCl (40%) were introduced to the mixture and after 5 min 0.1 gr TAA was added and the final solution was transferred to the autoclave maintained at 190 °C for 10 h (sample 1). The same experiment without HCl was performed to investigate the effect of HCl (sample 2). Fabrication of FTO/TiO2/CIS/PMP dyes/Pt-FTO: After cooling down to room temperature, the solution was transferred to a beaker under vigorous stirring for 5 minutes. After that, FTO/TiO2 was maintained for 10 h in the beaker. In this way, prepared nanoparticles together with dye were deposited on FTO/TiO2 film. Prepared FTO/TiO2/CIS/dye was washed with a little amount of water. Then counter-electrode was made from deposition of a Pt solution on FTO glass. Afterwards, this electrode was placed over FTO/TiO2/CIS/dye electrode [3].
3
3. Results and discussion The XRD results for samples 1 and 2 presented in Fig. 1 (a and b respectively) show broadened lines, which were assigned to tetragonal phase of CuInS2 (a = b = 5.5200 Å, and c = 11.1200Å) with space group of I-42d and JCPDS No. 38–0777.
Fig. 1. XRD patterns of a: sample 1 and b: sample 2.
No diffraction peaks relating to other species in Fig. 1a could be detected indicating that the obtained sample in the presence of HCl (sample 1) is pure, while XRD pattern of sample obtained without HCl (sample 2) revealed the presence of some impurity such as CuS and Cu2S in the final product which in turn confirms the fact that HCl is necessary for obtaining CuInS2 nanoparticles. Figs. 2a-d illustrate the SEM and TEM images of the PMP dyesCu(II) complex and CIS samples, respectively. Fig. 2a suggests that the complex is mainly composed of a large amount of sphere-like nanoparticles. Figs. 2b and c in Presented SEM images belongs to the prepared samples in presence and absence of HCl (samples 1 and 2, respectively). As clearly seen, in both synthetic conditions nanoparticles have been formed but nanoparticles prepared in acid absence have smaller sizes. Acid introducing to the reaction media causes decreasing of sulfide ion producing and subsequently decreases nucleation rate and 4
so nanoparticles will be coarser. According to the TEM image of the CIS (sample 1, Fig. 2d), the particle size of the product is about 10-15 nm.
Fig. 2. SEM images of a: PMP dyes-Cu(II) complex, b: sample 1, c: sample 2, and d: TEM image of sample 1.
Figs. 3a and b Show the FT-IR transition spectra of PMP dyes-Cu(II) complex and CIS nanoparticles obtained at 190 °C in presence of HCl (sample 1). In these spectra, stretching and bending vibrations of O–H appeared at
5
about 3425 and 1624 cm-1, respectively. The absorption peak at 1389 cm-1 corresponds to –COOH symmetry stretching vibrations, while absorptions at 2909 and 801 cm–1 are related to stretching and bending vibrations of C–H bond, respectively [4]. Moreover, the absorption peak at 570 cm-1 is due to Cu–O bond. Finally, the band at 1025 cm-1 is related to C–C vibrations [4]. According to Fig. 3b, it is obvious that there are not important peaks indicating that there is not any organic molecule absorbed on the surface of samples. In order to compare the effect of the adsorption mode on TiO2surface on the harvesting of light over a wide range of wavelengths, several tests were performed. The photovoltaic parameters obtained by measuring J-V curves (Figs. 3c and d) are shown in Table 1. The energy conversion efficiencies of the dye-sensitized solar cells using N719, CIS NPs, PMP dyes, and CIS-PMP dyes were 3.03, 0.12, 0.19, and 0.37%, respectively. Obviously a remarkable enhancement in efficiency takes place for the mixture of dye-nanoparticles compared to the pure dye or nanoparticles. Table 1 Energy conversion efficiency of DSSCs adsorbed with a: N719, b: CIS, PMP dyes and CIS-PMP dyes.
Dyes N719 CIS
PMP dyes CIS-PMP dyes
Voc (V) 0.75 0.52 0.48 0.54
Jsc (mA/cm2) 9.7 0.365 0.771 1.05
FF 0.42 0.62 0.51 0.66
η(%) 3.03 0.12 0.19 0.37
This enhancement is the result of barrier layer formation by nanoparticles which in turn increases electron lifetime [2]. Fig. 3e shows barrier layer and energy levels diagram of TiO2/CIS/PMP dyes. As clearly seen, LUMO of CuInS2 (-4.1 eV) is energetically lower than LUMO of dye (-3.51 eV) and higher than LUMO of TiO2 (-4.2 eV) revealing that electrons can be transferred from valance band of dye and CuInS2 to the conductance band of TiO2. (The examined highest occupied molecular orbital (HOMO) levels and the lowest unoccupied molecular orbital (LUMO) levels were calculated using Guo et al [2] method). The related reaction to form stoichiometric CuInS2 during hydrothermal process might be given in Eq (5). SO32- + H2O Æ SO42- + 2H+ + 2e
Eq. (1)
2Cu2+ + 2e Æ 2Cu+
Eq. (2) 6
2Cu++ S2- Æ Cu2S
Eq. (3)
2In3+ + 3S2- Æ In2S3
Eq. (4)
Cu2S + In2S3 Æ 2CuInS2
Eq. (5)
Fig. 3. FT-IR spectra of a: PMP dyes-Cu(II) complex, b: CIS nanoparticles and photocurrent-voltage curves of DSSCs adsorbed with c: N719, d: CIS, PMP dyes and CIS-PMP dyes, e: energy diagram of the photoanode.
In comparison with similar works, the current work is easier to control and more affordable. In this study, sodium sulfite was used instead of polyol solvents as a reducing agent to reduce of Cu2+ to Cu+ and this product (CuInS2) can be easily synthesized in aqueous media. Besides, PMP dyes were extracted by Cu2+ and new copper precursor was obtained which its using has many advantages such as: no need to any surfactant, possibility of 7
single step production of three layered solar cells, presentation a comprehensive method to increase of longevity of natural dyes and etc. 4. Conclusions Concisely, to improve the efficiency of solar cells, CuInS2 nanoparticles were synthesized using PMP dyesCu(II) and Na2SO3 as the new reagents in an acidic media through hydrothermal route. Pomegranate peel was used as a copper source. X-ray diffraction analysis showed that presence of HCl is crucial to synthesis of pure CIS nanoparticles. Finally FTO/TiO2/CIS/PMP dyes/Pt-FTO solar cell was prepared by single step deposition of dye and CIS on TiO2 nanoparticles for the first time and its performance was investigated. The results indicated that simultaneous use of dye and nanoparticles due to formation of barrier layer resulted in higher efficiencies. Acknowledgment Authors are grateful to council of University of Kashan for providing financial support to undertake this work by Grant No (159271/220). References [1] Zhou J, Li S, Gong X, Yang Y, Guo Y. Preparation of CuInS2 microspheres via a facile solution–chemical method. Mater Lett 2011; 65:2001–3. [2] Guo F, He J, Li J, Wu W, Hang Y, H Jianli. Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material. J Colloid Interf Sci 2013; 408:59–65. [3] Panahi-Kalamuei M, Salavati-Niasari M, Hosseinpour-Mashkani SM. Facile microwave synthesis, characterization, and solar cell application of selenium nanoparticles. J Alloy Compd 2014; 617:627–32. [4] Mohandes F, Salavati-Niasari M. Sonochemical synthesis of silver vanadium oxide micro/nanorods: Solvent and surfactant effects. Ultrason Sonochem 2013; 20:354–65.
8
Highlights ¾ CIS nanoparticles were synthesized using new starting reagents through hydrothermal route. ¾ Pomegranate marc peels (PMP) was used to prepare of copper precursor and dye solar cells. ¾ The XRD results indicated that presence of HCl is crucial to synthesis of pure CuInS2 (CIS). ¾ FTO/TiO2/CIS/PMP dyes/Pt-FTO solar cell was prepared for the first time.
9