Preparation of Platinum (Pt) Counter Electrode Coated by Electrochemical Technique at High Temperature for Dye-sensitized Solar Cell (DSSC) Application

Pt counter electrode was coated by electrochemical method. Electrolyte solution was synthesized by platinum (IV) choloride (PtCl4) powder dissolved in hydrochloric acid solution. Pt films were deposited on the FTO substrate. Deposition time of 10, 30 and 60 minutes, the coating current of 5, 10, 15 and 20 mA and electrolyte solution temperatures for Pt layer synthesis of 25, 30 and 40°C were varied. Surface morphology and optical properties was analyzed by digital microscopic and UV-vis spectrophotometer. Pt films exhibit uniform surface area highly for all the conditions of coating current in the deposition time of 30 and 40 minutes at 40°C. Transmittance values of Pt films deposited on FTO substrate has approximately of 5 to 50 % show that occur high reflection corresponding to dye molecule absorption increases. DSSC device was fabricated from the TiO2 standard and immersed in dye N719 for 24 hours. Efficiency was measured by solar simulator. Efficiency value obtains as high as 5.91 % for the coating current, deposition time and solution temperature of 15 mA, 30 minutes and 40°C. Summary, influence of temperature effects efficiency increasing. Pt counter electrode can be prepared easily and the suitable usefully for DSSC.


Introduction
The DSSC is photovoltaic which principle is similarly to light synthesis of leaves. Since 1994, M. Grätzel presented the DSSC concept [1]. After in 2008, the efficiency of DSSC was developed until to present which it can be increases as high as 10% under light intensity standard (100 mW/cm 2 , AM 1.5). Special characteristic is the electrons transfer occurred under electric field and reduction and oxidation reaction inner cell. The counter electrode synthesis was made from the Platinum (Pt), graphite (C) and catalyst element but this research used popularly the Pt counter electrode [2][3][4][5][6][7][8][9][10].
This work, we interested increasing high surface area and catalyse by Pt counter electrode. Pt counter electrode was coated by electrochemical method. It focus is on influence of electrolyte solution temperature for Pt layer synthesis to DSSC cell efficiency.

Preparation of the Pt counter electrode
Pt counter electrode was coated by electrochemical method which system consists of the dc power supply control, heating to electrolyte solution and substrate holder can adjust distance of electrode as shown in the Figure 1. Electrolyte solution was synthesized by platinum (IV) choloride (PtCl 4 ) powder (purity, 99.9%) dissolved in hydrochloric acid solution (HCl, 0.00156 M, purity of 99.99 %). Pt layer were deposited on the FTO substrate. Electrolyte concentration and the distance between positive and negative electrode (2 cm) were fixed under stir with magnetic stirrer continuously. The deposition time of 10, 30 and 60 minutes, the coating current of 5, 10, 15 and 20 mA and temperatures of 25, 30 and 40°C, respectively were varied.

Preparation of the TiO 2 working electrode
TiO 2 blocking layer was coated by spin coating technique which the solution was synthesized from Titanium diisopropoxidebis (C 16 H 28 O 6 Ti) 0.5 ml mixed with Isopropanal 10 ml. The TiO 2 working electrode was prepared by screen painting method on TiO 2 blocking/FTO substrate (commercial TiO 2 powder particle size of 32 and 5 nm, Alfa Aesar, USA, 99.999% purity and Degussa P25, AEROXIDE). After, The TiO 2 layer on the TiO 2 -blocking-layer/FTO/SLG specimens were immersed in the sensitizer ruthenium 535 bis-TBA solution (N719 dye) face-up for 24 hours at room temperature and then rinsed with ethanol.

Cells assembly
Two sides of DSSC cell were glued together using, for example, Parafilms, gasket SX117-60PF (SOLARONIX) or Ethylene-vinyl acetate (EVA). The seal was cut to form a frame around the glass electrodes. Heat from a hot air gun was then applied to the cells, thus forming the seal. Then, the   I I / 3 electrolyte (MPN-100, SOLARONIX) was injected into the cell. The area of the cell was typically 1.25 x 1.25 cm 2 and 0.7 x 1 cm 2 . Finally, the photocurrent conversion under standard AM 1.5 radiation (100 mW/cm 2 ) was measured.

Characterization tools
The characterization tools are X-ray diffraction (XRD) (PANalytical, EMPYREAN), UV-vis spectrophotometer (UV-1800) and Solar simulator (PEC-L11) were used for its structural and optical properties and photocurrent conversion of cell.

Results and Discussion
Image of the Pt films on FTO substrate by elctrochemical Method shows opaque light which it is black color as shown in the   The transmittance spectra of Pt film shows in the Figure 4 which transmittance light has very less. On other hand, the transmittance spectrum obtains up to 5 -50% for deposition time of 30 to 60 minutes. Show that, Pt counter electrode can be reflecting light into cell highly corresponding to increases photon absorption of dye-sensitizer. Thus, colour characteristic of Pt layer somewhat opaque light.
The photocurrent -voltage curve of DSSC device shows in the Figure 5. Parameter of performance has the current density ( SC J ) are 11.70 mA/cm 2

Conclusion
Influence of temperature effects to efficiency increasing which highest efficiency of DSSC cell can be obtain as high as 5.90%. Therefore, Pt counter electrode coated by chemical method can be prepared easily and the suitable usefully for DSSC application. The plane explicitly of Pt film on FTO substrate is (111) which it confirm the Pt crystalline layer. XRD patterns look like crystalline. Pt counter electrode can be reflecting light into cell highly corresponding to increases photon absorption of dye-sensitizer. Thus, colour characteristic of Pt layer somewhat opaque light. Our results show that this simple preparation of Pt layer can be applied as a counter electrode for DSSCs.