Development of Third Generation Solar Cells

1. BACKGROUND • OBJECTIVES • The development of a high-performance DSSC with good stability and feasible processibility is the goal of most studies. The key concerns of DSSC research include the improvement of device performance and stability. Hence, this study aims to: • increase the absorption band of the natural dye extract from the Philippine fruit Duhatby addition of metal ions, • diminish evaporation of the electrolyte system by utilizing a carrageenan gel electrolyte, and • construct a prototype device using duhat anthocyanins, and sealed using a silicone sealant. Transparent conducting FTO glass substrate Nanoporous TiO2 (anatase) thin film Adsorbed dye-sensitizer Carbon counter-electrode Figure 1.DSSC mechanism: Absorbed light excites a dye electron to the conduction band of the TiO2. The electron goes to the counter electrode by passing through an external load, completing the circuit. The original state of the dye is restored by electron donation from I-; I- is regenerated by reduction of I3- . Injection of electrolyte Figure 2.Fabrication of DSSC prototype. (a) (b) (c) Figure 8. Sealed DSSC device. Figure 5. The chemical structures of the three types of carrageenan. a) k-carrageenan; b) i-carrageenan; and c) λ-carrageenan.6 Figure 6. Incorporating the gel electrolyte into the DSSC: The carrageenan-dye-TiO2 layer was soaked in liquid iodide solution. Figure 6. The exponential decay of photovoltage output from the liquid electrolyte device displays the rapid decline of the cell’s stability over time. Figure 7. Sample exponential decay of photovoltage output for the k-carrageenan electrolyte devices. Figure 10. Testing the 1.5-V DSSC system Figure 4. The UV-vis spectra of the crude duhat anthocyanin extract with Cr3+ and with Fe3+. What are DSSCs? Dye-sensitized solar cells (DSSCs) are photoelectro-chemical devices that use photosensitization of wide-band-gap mesoporous oxide semiconductors. Why DSSCs? The impending decline of oil and gas sources on earth1 has motivated efforts to find cost-effective methods of utilizing renewable energy sources, e.g., sunlight. And making solar energy affordable is a leading Engineering Challenge for the 21st Century. The DSSC is a realistic alternative to the conventional silicon solar cell, because it promises competitive cost-to-efficiency ratio. ATENEO DE MANILA UNIVERSITY Katrina D. Malabanan, John Paul B. Garcia, Jenna Riz D. Pasco, and Erwin P. Enriquez* Department of Chemistry, School of Science and Engineering DSSC Market With solar cell production growing by 50% annually over the past six years, cumulative world production now stands at 3.8 GW.2 The market for DSSCs was established at $3.5 M in 2007, and is expected to reach $58.1 M in 2010.3 Development of Third Generation Solar Cells METAL ION-ANTHOCYANIN DYE-SENSITIZER CARRAGEENAN GEL ELECTROLYTE PROTOTYPE USING DUHAT A commercial silicone sealant was applied onto the DSSC prototypes until no leaks were observed, and ensuring that the conductive junctions of the device are not covered. The compatibility of the silicone sealant to the type of electrolyte was determined. The KI/ethylene glycol electrolyte solution proved to be suitable for the sealed DSSC prototypes, which generated an average of 0.344 - 0.361 V. These DSSCs were then connected in series to obtain a system with a total voltage output of 1.5 V. Gel electrolytes consisting of a liquid iodide solution in a carrageenan matrix were prepared and incorporated into DSSC prototypes. Figure 3.The equilibrium between the flavylium and the quinonoidal form of anthocyanins.5 Anthocyanins are responsible for the red, purple and blue colors in many fruits and flowers. Their visible absorption band shifts to the red upon complexation with metal ions, including aluminum, iron, tin, titanium, chromium and uranium.5 They were successfully employed as sensitizers for DSSC applications. The effect of added metal ions on the absorption band of anthocyanins from Syzigium cumini (or duhat) and their performance on dye-sensitized solar cells were investigated. Table 1. DSSC System Performance Addition of carrageenan significantly increased the conductivity of the electrolyte system. However, there was no apparent improvement in device performance in terms of photovoltage. Nevertheless, the polymer matrix diminished the evaporation of the I-/I3- redox couple, thereby improving device stability over time. No. of DSSCs Day 1 Day 2 Day 3 (V) (V) (V) Figure 9. The 1.5-V DSSC system connected in series. 5 1.51 1.53 1.61 The measured total photovoltage output of the DSSC system was only 86-89% of the expected system output. Measurements were made using an overhead projector lamp (intensity ≈ 633 W/m²) as the light source. The DSSC system was used to power a digital clock that runs on 1.2 V. The fabricated DSSC system using duhat dye extract proved to work reproducibly like a small battery. Additions of Sn2+, Cr3+ and Fe3+ showed increased absorption bands in comparison with the absorption bands of the crude anthocyanin extracts. Statistically, the addition of Cr3+ to the duhat dye increased the performance of the crude duhat dye as a sensitizer. It was also found that the crude duhat dye performed better than the duhat dye with Fe3+ ions. Literature Cited (1) Hart, P.; Skrebowski, C. Energy Bulletin. May 30, 2007 http://www.energybulletin.net/30537.html (2) http://st4tic.wordpress.com/2008/01/02/solar-cell-production-jumps-50-percent-in-2007 (3) http://solarcellsinfo.com/dyecell/node/2117 Acknowledgements Ms. Christine Querebillo for her MSE thesis paper. EPE acknowledges the Ateneo for a Professorial Chair grant. (4) Hagfeldt, A.; Grätzel, M. Molecular Photovoltaics. Acc. Chem. Res. 2000, 33, 269-277. (5) Cherepy, N. J.; Smestad, G. P.; Gratzel, M.; Zhang, J. J. Phys. Chem.B [Online] 1997, 101, 9342-9351. (6) Chaplin, M. “Carrageenan.” http://www. lsbu.ac.uk/water/hycar.html