Effect of Gel Electrolyte Mass Fraction on Dye-Sensitized Solar Cell Using Carbon Nanotube Composite-Papers

In recent years with the gradual focus on environmental issues, renewable energy sources have gained more and more attention, among which solar energy has gained widespread attention for its wide range and cleanliness, etc. This study investigates the new type of dye sensitized solar cells (DSSC), which are produced by the redox reaction of dyes. The aim of this study is to achieve unique dye sensitized solar cells by using carbon nanotube (CNT) composite papers (CNTCPs) which this study is developing.<br/>Since the CNTs contained in the CNTCP have metallic or semiconducting property, the use of the CNTCP as the cathode and anode of the DSSC has enabled the realization of a paper-DSSC with low cost and reduced environmental pollution. However, in our previous research, the paper-DSSC evaporated and leaked the contained electrolyte after about twenty minutes of operation when using a liquid electrolyte. To extend the life of the paper-DSSC, in this study, the safety and durability of the electrolyte is tried to improve by introducing a gel electrolyte, as follows:<br/>Firstly to make our CNTCPs, we add 48 mg of single-walled CNT and 70 mg of dispersant (Sodium Dodecyl Sulfate) in 36 ml of pure water. Next, this mixed solution is ultrasonically dispersed for 1 hour by using an ultrasonic homogenizer to prepare a CNT dispersion. 1 g of pulp is then blended in 1000 ml of pure water for 1 hour in a blender to obtain the pulp dispersion. The resulting metallic CNT dispersion is mixed with the pulp dispersion and the CNTCP is produced by the modified Japanese washi papermaking method. In the same way, 4 mg of semiconducting CNTs and 36mg of purple sweet potato color are dispersed in 18ml of water. The paper is then mixed with the pulp dispersion to produce a semiconducting CNTCP. The paper is then dried and shaped by heat pressing.<br/>Here, the gel electrolyte is made, the same as the liquid electrolyte used last time, this time still using iodine and potassium iodide as the main materials to carry out the redox reaction. 38.2 mg of iodine and 200 mg of potassium iodide are first dissolved in 20 mg of acetonitrile by heating in a water bath at 60 degrees centigrade, after it is completely dissolved, polyethylene glycol (PEG) was added, after it is dissolved again, the temperature is adjusted to 80 degrees centigrade and PolyVinylidene DiFluoride (PVDF), after all dissolved, the dispersion is placed in an oven at 70 degrees centigrade for 15 to 20 hours, when most of the acetonitrile has evaporated, the electrolyte at this point takes on a viscous liquid form.<br/>The electrolyte is dropped between the two laminated papers just made and when the remainder has evaporated, the electrolyte takes on a gel-like appearance. In our current study, this paper-DSSC was successfully made to generate electricity and extended its lifetime to more than 2 hours by using 1 g PEG and 1 g PVDF, obtaining fill-factor (FF; performance evaluation index) of 0.22 and a photovoltaic conversion efficiency of 6.9×10^-5%.<br/>In order to obtain higher photovoltaic conversion efficiency, the concentration ratio of PEG and PVDF is tried to be adjusted this time to compare the effect of this electrolyte on the photovoltaic conversion efficiency of paper-DSSCs at different ratios. Without changing condition for semiconductor electrodes, gel electrolytes with PEG: PVDF of 5:5, 6:4 and 4:6 are added into the paper-DSSCs as trial. As results, we found that changing the ratio of PEG and PVDF tended to affect the photovoltaic conversion efficiency. We are now trying to find the suitable condition for the ratio.<br/>We believe that desired paper-DSSCs with high photovoltaic conversion efficiency and lifetime can be obtained by using carbon nanotube composite paper and our approaches.