- Email: [email protected]
Influence of FTO glass cleaning on DSSC performance
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Influence of FTO glass cleaning on DSSC performance Katrin Gossen, Andrea Ehrmann
⁎
T
Bielefeld University of Applied Sciences, Faculty of Engineering and Mathematics, ITES, Bielefeld, Germany
A R T IC LE I N F O
ABS TRA CT
Keywords: DSSC Dye-sensitized solar cell FTO glass Solvent Cleaning Preparation
Dye-sensitized solar cells (DSSCs) are under investigation in diverse research groups, working with a broad variety of dyes and several electrolytes and semiconductors. In typical laboratory experiments, DSSCs are often built using glasses pre-coated with fluorine-doped tin oxide (FTO) to make them conductive. Comparing papers from different groups, these FTO glasses are cleaned before use by different solvents. Unexpectedly, our recent study showed that the choice of this solvent influences the efficiency gained with a DSSC as well as its longevity. Comparing cells prepared with uncleaned FTO glasses and with glasses cleaned with water, acetone, isopropanol or ethanol, showed highest efficiencies for the uncleaned glasses, while cleaning with acetone or ethanol resulted in reduced efficiency or longevity.
1. Introduction Since their first description in the scientific literature [1], dye-sensitized solar cells (DSSCs) are being investigated by diverse research groups. While DSSCs are not yet as efficient as silicon-based solar cells, they have the advantages to be preparable outside a clean room from low-cost, non-toxic materials. Using natural dyes, relatively small efficiencies were gained, starting from values of the order of magnitude 0.1%-1% for pure natural dyes without chemical modifications and without nanostructuring the semiconductor [2–9], while slightly higher values can be reached, e.g., by using a semiconductor prepared in the shape of nano-rods [10]. To develop these dyes and the other parts of DSSCs further, it is necessary to build cells as reliable and reproducible as possible, ideally with unchanged parameters between different studies. Even parts of the DSSCs which are mostly not in the focus of investigations, such as the pressure between both electrodes and the way how the catalyst (often graphite) is applied on the counter electrode, can significantly alter the efficiencies of DSSCs [11]. Another parameter which is sometimes mentioned in scientific papers about DSSCs, but has only scarcely been investigated yet is the cleaning process of the FTO (fluorine-doped tin oxide) glasses which are mostly used in laboratory experiments. More et al. compared ultrasonic bath sonication with and without subsequent heat treatment and found that the latter was preferable [12]. Other researchers used rinsing with de-ionised water and isopropanol for cleaning the FTO glass [13], cleaning with soap solution, ethanol and distilled water [14], ultra-sonication in ethanol [15], or ultra-sonication with acetone, ethanol and water [10], to name a few. Several other papers do not mention this apparently unimportant preparation step. Here we report on experimental investigation of the influence of cleaning commercially available FTO glasses with ethanol, water, acetone, or isopropanol in comparison with uncleaned FTO glasses. Our results show that this step should ideally be unified between different research groups to reach a better comparability of their results or at least be mentioned in the experimental descriptions.
⁎
Corresponding author. E-mail address: [email protected] (A. Ehrmann).
https://doi.org/10.1016/j.ijleo.2019.02.041 Received 8 January 2019; Accepted 12 February 2019 0030-4026/ © 2019 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
Fig. 1. FTO glasses (from left to right) uncleaned and cleaned with water, ethanol, isopropanol, and acetone.
2. Experimental Fluorine-doped tin oxide coated glasses (Man Solar, Petten, The Netherlands) were used as counter electrodes and with an additional TiO2 layer as front electrodes. The latter was dyed with forest fruit tea (Mayfair), mixing 2.5 g tea with 30 ml distilled water for 10 min and afterwards dyeing the TiO2 layers in this solution for 10 min, too. Excess dye was rinsed with distilled water. Afterwards the front electrodes were dried in the air. The resistances between the short edges of the counter electrodes were measured using a multimeter. The counter electrodes were carefully cleaned with water, ethanol, isopropanol or acetone by soft rubbing with gloves, or alternatively used without cleaning. All cleaned electrodes were afterwards rinsed with water to avoid any possible interaction of residual solvents on the FTO glasses with the electrolyte which may affect the DSSC efficiency. Resistances were measured again before a graphite layer was applied using a pencil (J. S. Staedtler). Three samples were prepared per solvent. The electrodes were fixed with the conductive sides pointing to each other, creating an efficient area of 6 cm², before they were filled with iodine/triiodide based electrolyte (Man Solar). Electrical characterization of the DSSCs was performed using a Keithley 2450 sourcemeter, illuminating the samples with a daylight lamp (halogen lamp with a color temperature of 3000 K) at 100 mW/cm². 3. Results and discussion Fig. 1 depicts the FTO glasses after cleaning, with the uncleaned one as the reference. It is clearly visible that cleaning with any solvent is sufficient to wash off most of the originally visible dirt and stains, while in each case some small stains or small fibers are still visible. Next, Table 1 shows the influence of cleaning on the measured resistances between both short edges of the FTO glasses. Firstly, it must be mentioned that the resistances before cleaning vary strongly. Tests showed that this effect is not related to the measurement method or the exact position of the multimeter tips, but there is a real variance within one batch of FTO glasses. Former experiments revealed that this finding is not problematic since short circuit currents reached with these differing FTO glasses vary much less than these resistance values. Comparing the resistances before and after cleaning, water and ethanol slightly reduce the resistances (not significant), while isopropanol and especially acetone lead to an increase in the resistance. To give an impression of the typical variance between the current-voltage (I–U) curves of three nominally identical DSSCs, Fig. 2 depicts I–U curves of cells with acetone-cleaned counter electrodes on day 0 and day 30. While the general performance is long-term stable and the short-circuit voltages even slightly increase during the first month after preparation, the slopes of the curves slightly change, indicating a fill factor reduction with time. At both times, all three nominally identical cells show very similar I–U curves. This finding is also valid for the other cells, with some larger deviations on day 30 for cells in which the electrolyte has visibly evaporated from the non-sealed cells. A comparison of the time-dependent efficiencies for cells with counter electrodes cleaned with the different solvents is depicted in Fig. 3. Firstly, all cells show the highest efficiencies on day 3 which is a common finding for DSSCs prepared with the materials used here. It should also be mentioned that in all cases the DSSCs still work on day 30 although they are not sealed. Table 1 Resistances R between both short edges of the FTO glasses before and after cleaning. Solvent
Rbefore / Ω
Rafter / Ω
Water Ethanol Isopropanol Acetone Uncleaned
76 86 76 71 80
62 ± 13 61 ± 8 102 ± 6 177 ± 23 n. a.
± ± ± ± ±
254
11 4 14 14 11
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
Fig. 2. Current-voltage (I–U) curves, measured on DSSCs with acetone cleaned counter electrodes on different days.
Fig. 3. Time-dependent efficiencies reached with counter electrodes cleaned with different solvents.
According to the measurements of the resistances of the FTO glasses, it could have been expected that water and ethanol, slightly reducing the measured resistances, would result in the highest efficiencies, while acetone, creating the highest resistances, would perform worst. This is not the case. Unexpectedly, the highest efficiencies were reached with the uncleaned counter electrodes, although these ones clearly contained residual dirt and stains (cf. Fig. 1). On the other hand, the longevity is best for water and acetone as cleaning agents, rated by the difference between days 0 and 30. If only day 18 – on which the electrolyte is not yet partly evaporated from the cells – is taken into account in this comparison, all cells but those cleaned with ethanol show a slight increase of the efficiency from day 0 to day 18. It must be mentioned, however, that most differences are not significant, as the error bars reveal. Nevertheless our examination underlines the importance of taking the cleaning process into account since it may influence the efficiency as well as the longevity of DSSCs prepared with the low-cost materials described here. 4. Conclusion Counter electrodes of DSSCs were cleaned with different solvents or used uncleaned for DSSC preparation. Combined with TiO2 dyed with an anthocyanin-based dye, efficiencies between (0.031 ± 0.002) % and (0.043 ± 0.004) % were reached directly after preparation, while values between (0.028 ± 002) % and (0.035 ± 0.004) % were gained on day 30. While not all deviations are significant, the large span between these extremal values underlines the importance of taking into account the cleaning process. Future investigations will concentrate on the possible additional influence of ultrasonic treatment or heat treatment to increase not only efficiency and longevity of DSSCs, but also the comparability of results gained by different research groups. Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this paper. References [1] B. O’Reagan, M. Grätzel, A low cost, high efficiency solar cell based on dye sensitized colloidal TiO2 films, Nature 353 (1991) 737–740.
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Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
[2] I. Juhász Junger, D. Werner, E. Schwenzfeier-Hellkamp, A. Ehrmann, Influence of illumination spectra on DSSC performance, Optik 177 (2019) 8–12. [3] S. Lucioli, C. Di Bari, C. Forni, A. Di Carlo, E. Barrajón-Catalán, V. Micol, P. Nota, F. Teoli, F. Matteocci, A. Frattarelli, E. Caboni, Anthocyanic pigments from elicited in vitro grown shoot cultures of Vaccinium corymbosum L., cv. Brigitta Blue, as photosensitizer in natural dye-sensitized solar cells (NDSSC), J. Photochem. Photobiol. B: Biol. 188 (2018) 69–76. [4] Q. Liu, N. Gao, D.J. Liu, J.L. Liu, Y.Z. Li, Structure and photoelectrical properties of natural photoactive dyes for solar cells, Appl. Sci. 8 (1697) (2018). [5] I. Juhász Junger, S.V. Homburg, T. Grethe, A. Herrmann, J. Fiedler, A. Schwarz-Pfeiffer, T. Blachowicz, A. Ehrmann, Examination of the sintering process dependent properties of TiO2 on glass and textile substrates, J. Photon. Energy 7 (2017) 015001. [6] A.A. Ludin, M.A.M. Al-Alwani, A.B. Mohamad, A.A.H. Kadhum, N.H. Hamid, M.A. Ibrahim, M.A.M. Teridi, T.M.A. Al-Hakeem, A. Mukhlus, K. Sopian, Utilization of natural dyes from Zingiber officinale leaves and Clitoria ternatea flowers to prepare new photosensitisers for dye-sensitised solar cells, Int. J. Electrochem. Sci. 13 (2018) 7451–7465. [7] T.Y. Kim, J.H. Kim, H.B. Kim, K.H. Park, J.W. Lee, S.Y. Cho, Adsorption and kinetics properties of TiO2 photoelectrode using Natural Paprika Oleoresin (Capsicum annuum L.) dye for dye-sensitized solar Cells, Int. J. Electrochem. Sci. 13 (2018) 3935–3947. [8] D. Sinha, D. De, A. Ayaz, Performance and stability analysis of curcumin dye as a photo sensitizer used in nanostructures ZnO based DSSC, Spectrochim. Act A – Mol. Biomol. Spectrosc. 193 (2018) 467–474. [9] A. Ehrmann, T. Blachowicz, Comment on ‘Dye-sensitized solar cells using Aloe Vera and Cladode of Cactus extracts as natural sensitizers’ [Chem.Phys. Lett. 679 (2017) 97–101], Chem. Phys. Lett. 714 (2019) 227–229. [10] P. Sanjay, K. Deepa, J. Madhavan, S. Senthil, Optical, spectral and photovoltaic characterization of natural dyes extracted from leaves of Peltophorum pterocarpum and Acalypha amentacea used as sensitizers for ZnO based dye sensitized solar cells, Opt. Mater. 83 (2018) 192–199. [11] F. Hölscher, P.-R. Trümper, I. Juhász Junger, E. Schwenzfeier-Hellkamp, A. Ehrmann, Raising reproducibility in dye-sensitized solar cells under laboratory conditions, J. Renew. Sustain. Energy 10 (2018) 013506. [12] V. More, V. Shivade, P. Bhargava, Effect of cleaning process of substrate on the efficiency of the DSSC, Trans. Indian Ceram. Soc. 75 (2016) 59–62. [13] P.J. Holliman, A. Connell, M. Davies, M. Carnie, D. Bryant, E.W. Jones, Low temperature sintering of aqueous TiO2 colloids for flexible, co-sensitized dyesensitized solar cells, Mater. Lett. 236 (2019) 289–291. [14] A. Agasti, S.S. Nemala, S. Mallick, P. Bhargava, Stability study of co-electrodeposited CZTS counter electrode for dye sensitized solar cells, Sol. Energy 176 (2018) 325–333. [15] R. Senthilkumar, S. Ramakrishnan, M. Balu, P.C. Ramamurthy, D. Kumaresan, One-step hydrothermal synthesis of marigold flower-like nanostructured MoS2 as a counter electrode for dye-sensitized solar cells, J. Solid State Electrochem. 22 (2018) 3331–3341.
256
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.com/locate/ijleo
Influence of FTO glass cleaning on DSSC performance Katrin Gossen, Andrea Ehrmann
⁎
T
Bielefeld University of Applied Sciences, Faculty of Engineering and Mathematics, ITES, Bielefeld, Germany
A R T IC LE I N F O
ABS TRA CT
Keywords: DSSC Dye-sensitized solar cell FTO glass Solvent Cleaning Preparation
Dye-sensitized solar cells (DSSCs) are under investigation in diverse research groups, working with a broad variety of dyes and several electrolytes and semiconductors. In typical laboratory experiments, DSSCs are often built using glasses pre-coated with fluorine-doped tin oxide (FTO) to make them conductive. Comparing papers from different groups, these FTO glasses are cleaned before use by different solvents. Unexpectedly, our recent study showed that the choice of this solvent influences the efficiency gained with a DSSC as well as its longevity. Comparing cells prepared with uncleaned FTO glasses and with glasses cleaned with water, acetone, isopropanol or ethanol, showed highest efficiencies for the uncleaned glasses, while cleaning with acetone or ethanol resulted in reduced efficiency or longevity.
1. Introduction Since their first description in the scientific literature [1], dye-sensitized solar cells (DSSCs) are being investigated by diverse research groups. While DSSCs are not yet as efficient as silicon-based solar cells, they have the advantages to be preparable outside a clean room from low-cost, non-toxic materials. Using natural dyes, relatively small efficiencies were gained, starting from values of the order of magnitude 0.1%-1% for pure natural dyes without chemical modifications and without nanostructuring the semiconductor [2–9], while slightly higher values can be reached, e.g., by using a semiconductor prepared in the shape of nano-rods [10]. To develop these dyes and the other parts of DSSCs further, it is necessary to build cells as reliable and reproducible as possible, ideally with unchanged parameters between different studies. Even parts of the DSSCs which are mostly not in the focus of investigations, such as the pressure between both electrodes and the way how the catalyst (often graphite) is applied on the counter electrode, can significantly alter the efficiencies of DSSCs [11]. Another parameter which is sometimes mentioned in scientific papers about DSSCs, but has only scarcely been investigated yet is the cleaning process of the FTO (fluorine-doped tin oxide) glasses which are mostly used in laboratory experiments. More et al. compared ultrasonic bath sonication with and without subsequent heat treatment and found that the latter was preferable [12]. Other researchers used rinsing with de-ionised water and isopropanol for cleaning the FTO glass [13], cleaning with soap solution, ethanol and distilled water [14], ultra-sonication in ethanol [15], or ultra-sonication with acetone, ethanol and water [10], to name a few. Several other papers do not mention this apparently unimportant preparation step. Here we report on experimental investigation of the influence of cleaning commercially available FTO glasses with ethanol, water, acetone, or isopropanol in comparison with uncleaned FTO glasses. Our results show that this step should ideally be unified between different research groups to reach a better comparability of their results or at least be mentioned in the experimental descriptions.
⁎
Corresponding author. E-mail address: [email protected] (A. Ehrmann).
https://doi.org/10.1016/j.ijleo.2019.02.041 Received 8 January 2019; Accepted 12 February 2019 0030-4026/ © 2019 Elsevier GmbH. All rights reserved.
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
Fig. 1. FTO glasses (from left to right) uncleaned and cleaned with water, ethanol, isopropanol, and acetone.
2. Experimental Fluorine-doped tin oxide coated glasses (Man Solar, Petten, The Netherlands) were used as counter electrodes and with an additional TiO2 layer as front electrodes. The latter was dyed with forest fruit tea (Mayfair), mixing 2.5 g tea with 30 ml distilled water for 10 min and afterwards dyeing the TiO2 layers in this solution for 10 min, too. Excess dye was rinsed with distilled water. Afterwards the front electrodes were dried in the air. The resistances between the short edges of the counter electrodes were measured using a multimeter. The counter electrodes were carefully cleaned with water, ethanol, isopropanol or acetone by soft rubbing with gloves, or alternatively used without cleaning. All cleaned electrodes were afterwards rinsed with water to avoid any possible interaction of residual solvents on the FTO glasses with the electrolyte which may affect the DSSC efficiency. Resistances were measured again before a graphite layer was applied using a pencil (J. S. Staedtler). Three samples were prepared per solvent. The electrodes were fixed with the conductive sides pointing to each other, creating an efficient area of 6 cm², before they were filled with iodine/triiodide based electrolyte (Man Solar). Electrical characterization of the DSSCs was performed using a Keithley 2450 sourcemeter, illuminating the samples with a daylight lamp (halogen lamp with a color temperature of 3000 K) at 100 mW/cm². 3. Results and discussion Fig. 1 depicts the FTO glasses after cleaning, with the uncleaned one as the reference. It is clearly visible that cleaning with any solvent is sufficient to wash off most of the originally visible dirt and stains, while in each case some small stains or small fibers are still visible. Next, Table 1 shows the influence of cleaning on the measured resistances between both short edges of the FTO glasses. Firstly, it must be mentioned that the resistances before cleaning vary strongly. Tests showed that this effect is not related to the measurement method or the exact position of the multimeter tips, but there is a real variance within one batch of FTO glasses. Former experiments revealed that this finding is not problematic since short circuit currents reached with these differing FTO glasses vary much less than these resistance values. Comparing the resistances before and after cleaning, water and ethanol slightly reduce the resistances (not significant), while isopropanol and especially acetone lead to an increase in the resistance. To give an impression of the typical variance between the current-voltage (I–U) curves of three nominally identical DSSCs, Fig. 2 depicts I–U curves of cells with acetone-cleaned counter electrodes on day 0 and day 30. While the general performance is long-term stable and the short-circuit voltages even slightly increase during the first month after preparation, the slopes of the curves slightly change, indicating a fill factor reduction with time. At both times, all three nominally identical cells show very similar I–U curves. This finding is also valid for the other cells, with some larger deviations on day 30 for cells in which the electrolyte has visibly evaporated from the non-sealed cells. A comparison of the time-dependent efficiencies for cells with counter electrodes cleaned with the different solvents is depicted in Fig. 3. Firstly, all cells show the highest efficiencies on day 3 which is a common finding for DSSCs prepared with the materials used here. It should also be mentioned that in all cases the DSSCs still work on day 30 although they are not sealed. Table 1 Resistances R between both short edges of the FTO glasses before and after cleaning. Solvent
Rbefore / Ω
Rafter / Ω
Water Ethanol Isopropanol Acetone Uncleaned
76 86 76 71 80
62 ± 13 61 ± 8 102 ± 6 177 ± 23 n. a.
± ± ± ± ±
254
11 4 14 14 11
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
Fig. 2. Current-voltage (I–U) curves, measured on DSSCs with acetone cleaned counter electrodes on different days.
Fig. 3. Time-dependent efficiencies reached with counter electrodes cleaned with different solvents.
According to the measurements of the resistances of the FTO glasses, it could have been expected that water and ethanol, slightly reducing the measured resistances, would result in the highest efficiencies, while acetone, creating the highest resistances, would perform worst. This is not the case. Unexpectedly, the highest efficiencies were reached with the uncleaned counter electrodes, although these ones clearly contained residual dirt and stains (cf. Fig. 1). On the other hand, the longevity is best for water and acetone as cleaning agents, rated by the difference between days 0 and 30. If only day 18 – on which the electrolyte is not yet partly evaporated from the cells – is taken into account in this comparison, all cells but those cleaned with ethanol show a slight increase of the efficiency from day 0 to day 18. It must be mentioned, however, that most differences are not significant, as the error bars reveal. Nevertheless our examination underlines the importance of taking the cleaning process into account since it may influence the efficiency as well as the longevity of DSSCs prepared with the low-cost materials described here. 4. Conclusion Counter electrodes of DSSCs were cleaned with different solvents or used uncleaned for DSSC preparation. Combined with TiO2 dyed with an anthocyanin-based dye, efficiencies between (0.031 ± 0.002) % and (0.043 ± 0.004) % were reached directly after preparation, while values between (0.028 ± 002) % and (0.035 ± 0.004) % were gained on day 30. While not all deviations are significant, the large span between these extremal values underlines the importance of taking into account the cleaning process. Future investigations will concentrate on the possible additional influence of ultrasonic treatment or heat treatment to increase not only efficiency and longevity of DSSCs, but also the comparability of results gained by different research groups. Conflict of interest The authors declare that there is no conflict of interest regarding the publication of this paper. References [1] B. O’Reagan, M. Grätzel, A low cost, high efficiency solar cell based on dye sensitized colloidal TiO2 films, Nature 353 (1991) 737–740.
255
Optik - International Journal for Light and Electron Optics 183 (2019) 253–256
K. Gossen and A. Ehrmann
[2] I. Juhász Junger, D. Werner, E. Schwenzfeier-Hellkamp, A. Ehrmann, Influence of illumination spectra on DSSC performance, Optik 177 (2019) 8–12. [3] S. Lucioli, C. Di Bari, C. Forni, A. Di Carlo, E. Barrajón-Catalán, V. Micol, P. Nota, F. Teoli, F. Matteocci, A. Frattarelli, E. Caboni, Anthocyanic pigments from elicited in vitro grown shoot cultures of Vaccinium corymbosum L., cv. Brigitta Blue, as photosensitizer in natural dye-sensitized solar cells (NDSSC), J. Photochem. Photobiol. B: Biol. 188 (2018) 69–76. [4] Q. Liu, N. Gao, D.J. Liu, J.L. Liu, Y.Z. Li, Structure and photoelectrical properties of natural photoactive dyes for solar cells, Appl. Sci. 8 (1697) (2018). [5] I. Juhász Junger, S.V. Homburg, T. Grethe, A. Herrmann, J. Fiedler, A. Schwarz-Pfeiffer, T. Blachowicz, A. Ehrmann, Examination of the sintering process dependent properties of TiO2 on glass and textile substrates, J. Photon. Energy 7 (2017) 015001. [6] A.A. Ludin, M.A.M. Al-Alwani, A.B. Mohamad, A.A.H. Kadhum, N.H. Hamid, M.A. Ibrahim, M.A.M. Teridi, T.M.A. Al-Hakeem, A. Mukhlus, K. Sopian, Utilization of natural dyes from Zingiber officinale leaves and Clitoria ternatea flowers to prepare new photosensitisers for dye-sensitised solar cells, Int. J. Electrochem. Sci. 13 (2018) 7451–7465. [7] T.Y. Kim, J.H. Kim, H.B. Kim, K.H. Park, J.W. Lee, S.Y. Cho, Adsorption and kinetics properties of TiO2 photoelectrode using Natural Paprika Oleoresin (Capsicum annuum L.) dye for dye-sensitized solar Cells, Int. J. Electrochem. Sci. 13 (2018) 3935–3947. [8] D. Sinha, D. De, A. Ayaz, Performance and stability analysis of curcumin dye as a photo sensitizer used in nanostructures ZnO based DSSC, Spectrochim. Act A – Mol. Biomol. Spectrosc. 193 (2018) 467–474. [9] A. Ehrmann, T. Blachowicz, Comment on ‘Dye-sensitized solar cells using Aloe Vera and Cladode of Cactus extracts as natural sensitizers’ [Chem.Phys. Lett. 679 (2017) 97–101], Chem. Phys. Lett. 714 (2019) 227–229. [10] P. Sanjay, K. Deepa, J. Madhavan, S. Senthil, Optical, spectral and photovoltaic characterization of natural dyes extracted from leaves of Peltophorum pterocarpum and Acalypha amentacea used as sensitizers for ZnO based dye sensitized solar cells, Opt. Mater. 83 (2018) 192–199. [11] F. Hölscher, P.-R. Trümper, I. Juhász Junger, E. Schwenzfeier-Hellkamp, A. Ehrmann, Raising reproducibility in dye-sensitized solar cells under laboratory conditions, J. Renew. Sustain. Energy 10 (2018) 013506. [12] V. More, V. Shivade, P. Bhargava, Effect of cleaning process of substrate on the efficiency of the DSSC, Trans. Indian Ceram. Soc. 75 (2016) 59–62. [13] P.J. Holliman, A. Connell, M. Davies, M. Carnie, D. Bryant, E.W. Jones, Low temperature sintering of aqueous TiO2 colloids for flexible, co-sensitized dyesensitized solar cells, Mater. Lett. 236 (2019) 289–291. [14] A. Agasti, S.S. Nemala, S. Mallick, P. Bhargava, Stability study of co-electrodeposited CZTS counter electrode for dye sensitized solar cells, Sol. Energy 176 (2018) 325–333. [15] R. Senthilkumar, S. Ramakrishnan, M. Balu, P.C. Ramamurthy, D. Kumaresan, One-step hydrothermal synthesis of marigold flower-like nanostructured MoS2 as a counter electrode for dye-sensitized solar cells, J. Solid State Electrochem. 22 (2018) 3331–3341.
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