A Comparative Study of Quasi-solid Nanoclay Based Electrolyte and Liquid Electrolyte Dye Sensitized Solar Cells
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A Comparative Study of Quasi-solid Nanoclay Based Electrolyte and Liquid Electrolyte Dye Sensitized Solar Cells Laura Main, Lakshmi Munukutla, Brian Fauss, Travis Curtis, and Arunachalanadar M. Kannan Arizona State University, Department of Engineering, 6075 S. Williams Campus Loop, Mesa, AZ 85212, U.S.A. ABSTRACT Dye sensitized solar cells (DSSCs) are currently being explored as a cheaper alternative to the more common silicon (Si) solar cell technology with improved performance in low light conditions and less sensitivity to varying angles of incident light. One of the major challenges facing DSSCs is loss of the liquid electrolyte, through evaporation or leakage, which lowers stability and leads to increased degradation. To address this, batches of gel electrolyte cells are fabricated with 7 wt% nanoclay gel electrolyte and liquid electrolyte and were evaluated at standard test conditions over time. The gel cells achieved efficiencies as high as 9.18% compared to the 9.65% achieved by the liquid cells. Over a period of 10 days, the liquid cells degraded less than 20% of its maximum efficiency. By contrast, the gel cell's efficiency did not decrease to 20% of its maximum efficiency until 45 days. After several measurements, the liquid cells showed visible signs of leakage through the sealant, whereas the gel cells did not. This resistance to leakage likely contributed to the improved performance of the quasi-solid cells over liquid electrolyte DSSCs. INTRODUCTION In 1991 Michael Grätzel and Brian O’Regan first introduced DSSCs with a conversion efficiency of 7.1% [1]. Since that time, new innovations with materials and design processes have resulted with a recorded efficiency of 12.3%, from a cell using a porphyrin dye and a Co(II/III)tris(bipyridyl)-based redox electrolyte [2]. DSSCs consist of a working electrode, which is coated with the dye soaked TiO2 nanoparticles, and is the electrode exposed to light, and the counter electrode that is coated with the catalyst material, usually platinum (Pt). Electrolyte fills the space between electrodes, and the electrons flow from working electrode through external circuit to the counter electrode. When the dye absorbs photons from the sun, it becomes photo excited, and injects an electron into the conduction band of the TiO2. Within the electrolyte a redox reaction takes place at the working electrode, which donates an electron to the dye, and at the cathode, the triiodide (I3-) accepts an electron from the Pt coated conductive glass, a reduction reaction takes place regenerating the redox couple, and the cycle is completed without causing permanent chemical transformation of any material involved.
The electrolyte facilitates two important tasks in the DSSC process. It serves as the transport mechanism for the redox mediator from the TiO2 electrode to the counter electrode and also serves to regenerate the dye molecule at the TiO2 side, which has been oxidized following the electron injection into the conduction band of the TiO2. This is very important because it prev
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