A study of TiO 2 binder-free paste prepared for low temperature dye-sensitized solar cells
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Klaudia Wagner and David Officer Intelligent Polymer Research Institute, University of Wollongong, Innovation Campus, Fairy Meadow, New South Wales 2519, Australia (Received 7 May 2012; accepted 16 October 2012)
A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2 suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical performance of TiO2 electrodes, cast as single layers, was dependent on the thermal treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent of residual organics and found that acetates from the TiO2 precursor preparation were retained within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness 4 lm produced an energy conversion efficiency as high as 5.4% using this simple thermal treatment.
I. INTRODUCTION
Since the pioneering work of O’Regan and Grätzel in 1991,1 there has been great interest by the research community to understand the fundamental interactions of components (i.e., semiconductor oxide, sensitizer, and electrolyte) within the dye-sensitized solar cell (DSSC). This focus has led to many refinements in both materials and processes, which have improved the energy conversion efficiency of conventional DSSCs to 12.3%.2 A prime area of development has been centered on the mesoporous TiO2 architecture, which is used as high surface area electrodes for electron transport. TiO2 electrodes for DSSC are typically prepared by coating with a viscous paste prepared with organic binders onto a conducting glass substrate, followed by thermal treatment at temperatures .400 °C to allow organic compound elimination and subsequent particle binding and adhesion to the substrate.3 Currently, a key driver in the commercialization of DSSCs is the preparation of robust TiO2 electrodes at low temperature (#150 °C). This reduction in process temperature opens up the possibility of using polymer substrates in continuous roll-to-roll processing. Several process methods have been explored in the preparation of low temperature electrodes. They include mechanical compression,4–9 hydrothermal necking of a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.354 488
J. Mater. Res., Vol. 28, No. 3, Feb 14, 2013
titanium salts,10–12 ultraviolet (UV)–O3 curing,13–15 and microwave sintering.16,17 Although the compression method in combination with UV–O3 treatment has reported an efficiency of 7.6% on indium tin oxide (ITO)/polyethylene naphtalate (PEN), integration of such a process in DSSC device fabrication remains challenging. Casting of films onto substrates is by far the preferred method of preparing electrodes for DSSC. However, additives for low temperature TiO2 paste must provide adequate viscosity and volatility to produce uniform porous structures. An interesting method reported by Park et al.18,19 utilizes a binder-free formulation by adding
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