DEVELOPMENT OF DYE SENSITIZED ORGANIC SOLAR CELLS USING ECOFRIENDLY DYES EXTRACTED FROM FROM Epipremnum Aureum AND Acalypha Godseffia Sunday Chukwuemeka Emmanuel, Dr. N. Ananthi, Dr. M. S. P Subathra
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[email protected] Key words: TiO2, DSSC, natural dyes, ITO glass slides, carbon soot, sintering Abstract In this study, we investigated the photovoltaic efficiency of DSSC (Dye Sensitized Solar Cell) using Two different organic dyes extracted from natural sources namely Acalypha godseffia and Epipremnum aureum Commercially obtained TiO2 powder, coated over the conducting glass substrate was used as the photo anode and the same coated with carbon soot was used as the photo cathode. UV spectrophotometer and photoluminescence spectrophotometer was used to characterize the dyes to find their absorption and emission maxima respectively. X- Ray diffractometer was used to characterize the TiO2 electrode film. SEM analysis was also carried out to study the surface morphology. The life and efficiency of DSSC can be improved by studying the dye absorption process and the thickness, size and shape of TiO2 coating. Thus, low cost solar cells can be developed with significant power conversion efficiency I. INTRODUCTION Depletion of fossil fuels has led the world to shift from the conventional energy sources to renewable energy to meet the growing energy demand. Although the process is gradual but the potential of renewable energy has been well talked about in the past decade. The conversion of solar energy into different forms has been the core of the research for the recent past years. DSSCs have been attracting attention of both researchers and industries worldwide since 1991. Due to its low material cost, easy and inexpensive methods of fabrication and reasonably good power conversion efficiency, DSSCs are being considered to be a potential alternative to expensive conventional inorganic solar cells. There has been a continuous effort in searching for affordable organic solar energies among which dye-sensitized solar cells thus far demonstrate the highest energy conversion efficiency, and have been regarded as the most prospective technology. Unlike silicon solar cells, electrons and holes in a DSSC are transported in two different phases, TiO2 and electrolyte respectively, and because of which the chances of recombination in the cell become low. Hence, DSSCs do not require ultra-high pure materials unlike inorganic solar cells. DSSC fabricated with the inclusion of Nano crystalline materials has been effective in diverting from the classical solid state junction devices. In this study two different organic dyes extracted from natural sources namely Acalypha godseffia and Epipremnum aureum were used to sensitize the DSSC.
II. EXPERIMENTAL A. Materials
The chemicals used for the experiment were pure and of analytical grade. They were purchased and used as received. The chemicals used were stannous chloride, methanol, acetone, pure Iodine crystals, Potassium iodide, and Poly ethylene glycol. The glassware (test tubes, glass rod, beakers, etc.) were procured from Borosil, India. Indium Tin Oxide conductive glass slides (75 mm × 25 mm× 1.1 mm) were procured from Sigma Aldrich. Sunlight was used as the light source. C. Preparation of electrolyte Pure iodine crystals and potassium iodide were taken in the ratio ~ 1: 6.5 respectively and dissolved in appropriate quantity of poly ethylene glycol. This has to be prepared freshly. D. Deposition of catalyst Carbon soot from the candle was deposited on to the conducting side of the ITO glass slide. This was used as the catalyst. E. Extraction of dye Methanol was used as the solvent for the extraction of dyes from natural sources F. Construction A dye-sensitized solar cell consists of four main parts, all sealed between conductive glass. The first major component of a DSSC is the semiconductor. Titanium (IV) Oxide was used for this purpose. This serves to act as an electron transfer medium, and causes electrons to flow through the circuit.The next component of the cell is the photo-sensitized dye. In this study natural organic dyes, such as Acalypha godseffia and Epipremnum aureum were used. When the dye is struck by photons, it absorbs them and donates electrons to the TiO2 semiconductor. This causes current to flow through the circuit. Between the TiO2 and the counter electrode is an electrolyte solution. Iodide solution was used. This electrolyte is responsible for carrying charge between the electrode and counter electrode. The charge is carried between the redox reaction from I3 - to I-. The rate of this reaction is critical in determining the efficiency of the solar cell. The final component of a DSSC is the catalyst. Carbon soot was used as the catalyst in this work. It serves to catalyze the reduction of I3
- to I-. Fig. 1 Schematic representation of Dye Sensitized Solar Cell
G. Flow chart Mask with Scotch tape on the conducting side of ITO glass.
Apply TiO2 paste and flatten it on the same side of the ITO Sinterglass. the TiO2 paste at 350 °C for 30 min in a furnace and add the dye drop wise on to the TiO2 surface. Allow it to dry for 3 min. Then add the electrolyte drop wise.
Coat another ITO slide with carbon soot which serves as the counter electrode. Place the electrodes facing each other with the help of binder clips.
Cell sample
The two electrodes (photo anode and cathode) should be combined as soon as the electrolyte is added. Leads were taken with the help of copper wires form each electrode using alligator clips. Voltage and current measurements were done using a multimeter. III. RESULTS AND DISCUSSION A. UV-Vis spectroscopic studies The maximum absorption and the optical density were measured for all the dyes and TiO2.
Fig.2 Absorption spectrum of TiO2 (semiconductor)
UV-VISIBLE spectrum of Epipremnum Aureum Dye
UV-VISIBLE spectrum of Acalypha godseffiana
IV Characteristics of Epipremnum aureum VOC = 0.77 v JSC = 7.58 mA/cm2 Im(Maximum current) = 6 mA/cm2 Vm(Maximum voltage) = 0.56 v
ff(Fill factor) = ImVm/JSCVOC = 0.576 ɳ (Efficiency) = [VOC*JSC*ff/100]*100 = 3.362%
IV Characteristics of Acalypha godseffia VOC = 0.77 v JSC = 9.21 mA/cm2 Im(Maximum current) = 7.95 mA/cm2 Vm(Maximum voltage) = 0.55 v
ff(Fill factor) = ImVm/JSCVOC = 0.61656 ɳ (Efficiency) = [VOC*JSC*ff/100]*100 = 4.372%
Dye extracted from Acalypha godseffia Leave
Dye Extracted from Epipremnum Aureum
Cell made from Epipremnum Aureum Dy
Cell made from Acalypha godseffia Dye
IV. CONCLUSION The successful use of DSSC depends on stability and conversion efficiency. Stability has been found to be affected in DSSC when exposed to UV light It can be concluded, that currently available DSSC-technology is not applicable for a largescale implementation. Cheaper cell components (organic dyes, other iodide source), which give high conversion efficiencies and a good long term stability, need to be developed before the price for a DSSC can compete with other thin film solar cells. Although Organic dyes have higher molar extinction coefficients, their lower stability limits them to be preferred. The efficiency has already risen from 7%, of the initial cells two decades back, to 11% leading to the invasion of Dye sensitized solar cells commercially over the conventional Si based solar cells in the coming future. ACKNOWLEDGEMENT I acknowledges Karunya University for providing a comfortable environment for me to carry out my work. I also acknowledge chemistry department karunya university for provision of Facility and analytical support. The authors acknowledge Department of Electrical and Electronic Engineering for their support and I also thank my guide Dr. M. Ananthi and Dr. Subathra for their help and support and help.
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