COMPARISON BETWEEN SPIN COATING AND MAGNETRON ...
COMPARISON BETWEEN SPIN COATING AND MAGNETRON SPUTTERING Pt THIN FILMS AIMING SOLAR CELLS R. S. Moraes1, R. L. P. Gonçalves4, C. Stegemann1, A. S. da Silva Sobrinho1, D. A. Duarte2,3, M. Massi1,4 D. M. G. Leite1 and E. Saito4 1
Plasma and Process Laboratory, Technological Institute of Aeronautics, São José dos Campos, SP, Brazil. 2 Catholic University of Santa Catarina, Joinville, SC, Brazil. 3 Center of Mobility Engineering, Federal University of Santa Catarina, Joinville, SC, Brazil. 4 Institute of Science and Technology, Federal University of São Paulo, São José dos Campos, SP, Brazil. Dye-sensitized solar cells (DSCs), known as photoelectrochemical solar cells, are extensively studied because the low cost materials. To ensure efficiently charge transport in this kind of devices, it's important that the counter-electrode (CE) with platinum catalytic layer improve electron collection, catalyzing iodide-tri-iodide reaction. In this work two different methods was employed to form the Pt catalyst film, magnetron sputtering and spin coating. To sputtering method, a pure platinum target was sputtered by argon, depositing metallic platinum thin films. For spin coating method, a commercial Solaronix Platisol T liquid paint was used as platinum catalyst. The thickness of films was measured by a profilometer and sheet resistance by four-point probe measurements. The former tests was carried out and thickness for sputtering method was approximately 393 nm. Electrical characterization showed approximately 395 mΩ/□ for metallic platinum obtained by sputtering, quite smaller than 7.8 Ω/□ measured for films obtained by spin coating. To evaluate the catalytic activity first was employed a simple method with hydrogen peroxide. The presence of tiny bubbles of oxygen was observed, suggesting the presence of activated platinum for both methods. To confirm this, CV (Cyclic Voltammetry) technique was used to better analyze the catalytic activity of platinum layer.
Keywords: dye-sensitized solar cell, counter-electrode, Pt catalyst film.
Introduction Since Grätzel and O'Regan started in 1991 [1], dye-sensitized solar cells are extensively studied around the world. Although the efficiency of this kind of cells is not competitive with silicon based solar cells yet, low cost materials and inexpensive manufacturing processes are attractive for organic solar cells [2,3,4,5,6]. The counter electrode consist of a transparent conductive oxide (TCO) glass and the platinum catalyst film. This platinum film is important to improve the electron collection, catalyzing iodide-triiodide reaction that occurs in the interface between counter electrode and electrolyte, increasing the efficiency of the solar cell [7]. In this work, two different methods were tested to deposit a platinum thin film on TCO. The former technique was magnetron sputtering that provides a metallic thin film. Platinum presents a high value of
sputtering yield, providing higher values of deposition rates [8]. The other technique employed to deposit platinum thin film was spin coating. This is a consolidate technique used to dye solar cells applications [7,9]. Parameters related to this two processes was varied and the response was evaluated on the films properties. Experimental part Two different kinds of methods were used to form the platinum films, magnetron sputtering and spin coating. A DC sputtering system was employed, which a 1.33 inch pure platinum target was sputtered by argon. The principal processes parameters are 20W of DC power, pressure of 3.2 mTorr during deposition and distance between target-sample of 20 mm and five minutes of deposition. In the spin coating processes, a commercial Solaronix Platisol T liquid paint was used as platinum catalyst. Four different speeds was tested, 1000, 2000, 3000 and 4000 rpm and 20 s was the total time processes for each test. After the spin coating processes the samples were fired by heat treatment at 450°C. The thickness of films was measured by a profilometer and sheet resistance by four-point probe measurements. Cyclic Voltametry measurements were performed by potentiostatic control by commercial equipment (Metrohm) with Ag/Ag+ as a reference electrode, pure platinum wire as a counter electrode in commercial Solaronix MPN-50 electrolyte solution (3-methoxypropionitrile solvent). Results and discussion
Current density (mA/cm2)
The film thickness for sputtering method was approximately 393 nm that is enough to provide charge-transport at the counter electrode and electrolyte interface [10,11]. Electrical characterization showed approximately 395 mΩ/□ for metallic platinum obtained by sputtering, quite smaller than 7.8 Ω/□ measured for films obtained by spin coating. Was not possible to measure the thickness of spin coated films by profilometer because films were too thin. Different speeds in spin process don't change the sheet resistance of films. To evaluate the catalytic activity first was employed a simple method with hydrogen peroxide. The presence of tiny bubbles of oxygen was observed, suggesting a presence of activated platinum for both methods. The voltametric response suggests a strong catalytic response attributed to at least one redox pair [7]. Figure 1 shows the voltammetry curve for spin coating film. Further studies have to be performed to evaluate the adhesion of platinum thin film and their consequence on the sequential redox reaction. 3 2 1 0 -1 -2 -3 -4 -1.2
-0.8
-0.4
0.0
0.4
0.8
Potential (V vs. Ag/Ag+) Fig. 1 – Voltammetry curve obtained in Solaronix MPN-50 electrolyte solution at 40mV.s-1.
Conclusions Platinum catalyst films were deposited onto TCO. Two different methods was employed. Sputtered films presented lower sheet resistance than spin coated films, showing that metallic films have highest conductivities. In relation of charge transport efficiency for these counter electrodes, qualitative method with hydrogen peroxide showed that the presence of tiny bubbles of oxygen suggested a presence of activated platinum for both methods. To confirm this hypothesis, CV tests were carried out in spin coated platinum films, showing that there at least a redox pair, confirming the presence of activated platinum. CV analysis must to be realized to metallic platinum films to compare with spin coated films analysis.
References 1. O’REGAN, B.; GRÄTZEL, M. A low-cost, high-efficiency solar cell based on dyesensitized colloidal TiO2 films. Nature, v. 353, p. 737, 1991. 2. HAGFELDT, A. et al. Dye-sensitized solar cells. Chemical reviews, v. 110, n. 11, p. 6595-663, 2010. 3. JENA, A. et al. Dye Sensitized Solar Cells: A Review. Transactions of the Indian Ceramic Society, v. 71, n. 1, p. 1-16, 2012. 4. JUNG, H.; LEE, J.-K. Dye Sensitized Solar Cells for Economically Viable Photovoltaic Systems. The Journal of Physical Chemistry Letters, v. 4, n. 10, p. 1682-1693, 2013. 5. MARTINSON, A. et al. New architectures for dye-sensitized solar cells. Chemistry - A European Journal, v. 14, n. 15, p. 4458-67, 2008. 6. GRÄTZEL, M. Recent advances in sensitized mesoscopic solar cells. Accounts of chemical research, v. 42, n. 11, p. 1788-98, 2009. 7. ZHAO, C. et al. Screen ‐ printed Pt counter electrodes exhibiting high catalytic activity. Chinese Journal of Catalysis, v. 35, n. 2, p. 2-7, 2014. 8. LAEGREID, N.; WEHNER, G. Sputtering Yields of Metals for Ar+ and Ne+ Ions with Energies from 50 to 600 ev. Journal of Applied Physics, v. 32, n. 3, p. 365369, 1961. 9. GRANQVIST, C. Transparent conductors as solar energy materials: A panoramic review. Solar Energy Materials and Solar Cells, v. 91, n. 17, p. 1529-1598, 2007. 10. FANG, X. et al. Effect of the thickness of the Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell. Journal of Electroanalytical Chemistry, v. 570, n. 2, p. 257-263, 2004. 11. FANG, X. et al. Performances characteristics of dye-sensitized solar cells based on counter electrodes with Pt films of different thickness. Journal of Photochemistry and Photobiology A: Chemistry, v. 164, p. 179-182, 2004. Acknowledgement: CAPES, CNPq
Plasma and Process Laboratory, Technological Institute of Aeronautics, São José dos Campos, SP, Brazil. 2 Catholic University of Santa Catarina, Joinville, SC, Brazil. 3 Center of Mobility Engineering, Federal University of Santa Catarina, Joinville, SC, Brazil. 4 Institute of Science and Technology, Federal University of São Paulo, São José dos Campos, SP, Brazil. Dye-sensitized solar cells (DSCs), known as photoelectrochemical solar cells, are extensively studied because the low cost materials. To ensure efficiently charge transport in this kind of devices, it's important that the counter-electrode (CE) with platinum catalytic layer improve electron collection, catalyzing iodide-tri-iodide reaction. In this work two different methods was employed to form the Pt catalyst film, magnetron sputtering and spin coating. To sputtering method, a pure platinum target was sputtered by argon, depositing metallic platinum thin films. For spin coating method, a commercial Solaronix Platisol T liquid paint was used as platinum catalyst. The thickness of films was measured by a profilometer and sheet resistance by four-point probe measurements. The former tests was carried out and thickness for sputtering method was approximately 393 nm. Electrical characterization showed approximately 395 mΩ/□ for metallic platinum obtained by sputtering, quite smaller than 7.8 Ω/□ measured for films obtained by spin coating. To evaluate the catalytic activity first was employed a simple method with hydrogen peroxide. The presence of tiny bubbles of oxygen was observed, suggesting the presence of activated platinum for both methods. To confirm this, CV (Cyclic Voltammetry) technique was used to better analyze the catalytic activity of platinum layer.
Keywords: dye-sensitized solar cell, counter-electrode, Pt catalyst film.
Introduction Since Grätzel and O'Regan started in 1991 [1], dye-sensitized solar cells are extensively studied around the world. Although the efficiency of this kind of cells is not competitive with silicon based solar cells yet, low cost materials and inexpensive manufacturing processes are attractive for organic solar cells [2,3,4,5,6]. The counter electrode consist of a transparent conductive oxide (TCO) glass and the platinum catalyst film. This platinum film is important to improve the electron collection, catalyzing iodide-triiodide reaction that occurs in the interface between counter electrode and electrolyte, increasing the efficiency of the solar cell [7]. In this work, two different methods were tested to deposit a platinum thin film on TCO. The former technique was magnetron sputtering that provides a metallic thin film. Platinum presents a high value of
sputtering yield, providing higher values of deposition rates [8]. The other technique employed to deposit platinum thin film was spin coating. This is a consolidate technique used to dye solar cells applications [7,9]. Parameters related to this two processes was varied and the response was evaluated on the films properties. Experimental part Two different kinds of methods were used to form the platinum films, magnetron sputtering and spin coating. A DC sputtering system was employed, which a 1.33 inch pure platinum target was sputtered by argon. The principal processes parameters are 20W of DC power, pressure of 3.2 mTorr during deposition and distance between target-sample of 20 mm and five minutes of deposition. In the spin coating processes, a commercial Solaronix Platisol T liquid paint was used as platinum catalyst. Four different speeds was tested, 1000, 2000, 3000 and 4000 rpm and 20 s was the total time processes for each test. After the spin coating processes the samples were fired by heat treatment at 450°C. The thickness of films was measured by a profilometer and sheet resistance by four-point probe measurements. Cyclic Voltametry measurements were performed by potentiostatic control by commercial equipment (Metrohm) with Ag/Ag+ as a reference electrode, pure platinum wire as a counter electrode in commercial Solaronix MPN-50 electrolyte solution (3-methoxypropionitrile solvent). Results and discussion
Current density (mA/cm2)
The film thickness for sputtering method was approximately 393 nm that is enough to provide charge-transport at the counter electrode and electrolyte interface [10,11]. Electrical characterization showed approximately 395 mΩ/□ for metallic platinum obtained by sputtering, quite smaller than 7.8 Ω/□ measured for films obtained by spin coating. Was not possible to measure the thickness of spin coated films by profilometer because films were too thin. Different speeds in spin process don't change the sheet resistance of films. To evaluate the catalytic activity first was employed a simple method with hydrogen peroxide. The presence of tiny bubbles of oxygen was observed, suggesting a presence of activated platinum for both methods. The voltametric response suggests a strong catalytic response attributed to at least one redox pair [7]. Figure 1 shows the voltammetry curve for spin coating film. Further studies have to be performed to evaluate the adhesion of platinum thin film and their consequence on the sequential redox reaction. 3 2 1 0 -1 -2 -3 -4 -1.2
-0.8
-0.4
0.0
0.4
0.8
Potential (V vs. Ag/Ag+) Fig. 1 – Voltammetry curve obtained in Solaronix MPN-50 electrolyte solution at 40mV.s-1.
Conclusions Platinum catalyst films were deposited onto TCO. Two different methods was employed. Sputtered films presented lower sheet resistance than spin coated films, showing that metallic films have highest conductivities. In relation of charge transport efficiency for these counter electrodes, qualitative method with hydrogen peroxide showed that the presence of tiny bubbles of oxygen suggested a presence of activated platinum for both methods. To confirm this hypothesis, CV tests were carried out in spin coated platinum films, showing that there at least a redox pair, confirming the presence of activated platinum. CV analysis must to be realized to metallic platinum films to compare with spin coated films analysis.
References 1. O’REGAN, B.; GRÄTZEL, M. A low-cost, high-efficiency solar cell based on dyesensitized colloidal TiO2 films. Nature, v. 353, p. 737, 1991. 2. HAGFELDT, A. et al. Dye-sensitized solar cells. Chemical reviews, v. 110, n. 11, p. 6595-663, 2010. 3. JENA, A. et al. Dye Sensitized Solar Cells: A Review. Transactions of the Indian Ceramic Society, v. 71, n. 1, p. 1-16, 2012. 4. JUNG, H.; LEE, J.-K. Dye Sensitized Solar Cells for Economically Viable Photovoltaic Systems. The Journal of Physical Chemistry Letters, v. 4, n. 10, p. 1682-1693, 2013. 5. MARTINSON, A. et al. New architectures for dye-sensitized solar cells. Chemistry - A European Journal, v. 14, n. 15, p. 4458-67, 2008. 6. GRÄTZEL, M. Recent advances in sensitized mesoscopic solar cells. Accounts of chemical research, v. 42, n. 11, p. 1788-98, 2009. 7. ZHAO, C. et al. Screen ‐ printed Pt counter electrodes exhibiting high catalytic activity. Chinese Journal of Catalysis, v. 35, n. 2, p. 2-7, 2014. 8. LAEGREID, N.; WEHNER, G. Sputtering Yields of Metals for Ar+ and Ne+ Ions with Energies from 50 to 600 ev. Journal of Applied Physics, v. 32, n. 3, p. 365369, 1961. 9. GRANQVIST, C. Transparent conductors as solar energy materials: A panoramic review. Solar Energy Materials and Solar Cells, v. 91, n. 17, p. 1529-1598, 2007. 10. FANG, X. et al. Effect of the thickness of the Pt film coated on a counter electrode on the performance of a dye-sensitized solar cell. Journal of Electroanalytical Chemistry, v. 570, n. 2, p. 257-263, 2004. 11. FANG, X. et al. Performances characteristics of dye-sensitized solar cells based on counter electrodes with Pt films of different thickness. Journal of Photochemistry and Photobiology A: Chemistry, v. 164, p. 179-182, 2004. Acknowledgement: CAPES, CNPq
