Addressing Bottlenecks in Dye-sensitized Solar Cell Manufacture Using Rapid Near-infrared Heat Treatments
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Addressing Bottlenecks in Dye-sensitized Solar Cell Manufacture Using Rapid Near-infrared Heat Treatments Trystan Watson, Cecile Charbonneau, Matthew Carnie, Ian Mabbett, Martyn Cherrington and David Worsley* SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation and Knowledge Centre, Baglan, Port Talbot, UK, SA12 7AX. * Corresponding author : [email protected] ABSTRACT A primary challenge to the industrial uptake of dye-sensitized solar cells (DSC) is the ability to improve manufacturing efficiency. New thinking is required in terms of lowering cost, improving the process steps and increasing throughput. The typical manufacture of a DSC contains a number of long process steps; the sintering and dyeing of the TiO2 are prime examples. The current solution is to batch process on rigid substrates or use long energy intensive convection ovens for flexible metal substrates. Here we present a method for reducing some of the bottlenecks in the manufacturing process using near infra red radiation to speed up the thermal treatment of TiO2 and silver inks reducing their processing times to 12 and 2 seconds from normal process times of 30 and 10 minutes respectively. INTRODUCTION The development of the dye-sensitized solar cell (DSC) by Grätzel and co-workers in the early 1990s has drawn considerable attention as a low cost alternative to conventional silicon solar cells [1–4]. A DSC typically consists of a mesoporous layer of TiO2 applied to a conducting substrate such as glass (with transmitting conducting oxide applied) or titanium metal. The TiO2 layer is sensitized with a monolayer of dye (often Ru based) which absorbs photons in the visible region and becomes excited. The electrons are subsequently injected into the conduction band of the TiO2 whereby they percolate between TiO2 particles to the conducting substrate electrode. After passing through the external circuit the electrons are reintroduced to the dye via an electrolyte (frequently an iodide/triiodide (I-/I3-) redox couple) mediated by a platinised counter electrode. Key challenges exist when considering the transition of dye-sensitized solar cells from the laboratory bench to the factory floor with a number of industrialisation projects aimed at taking DSC technology to flexible roll to roll manufacture [5]. Typically a laboratory type DSC cell takes up to 24 hours to build rendering some of the practical methodologies infeasible for a continuous roll to roll process. Figure 1 shows a manufacturing scheme for a DSC in a typical laboratory environment where no time constraints are applied in order to maximise efficiency. It can be seen that there are a number of rapid processes and a number of “bottlenecks”. The steps that take more than a few minutes are TiO2 sintering and dyeing, Pt heat treatment and Ag sintering for current collection. This paper focuses on the sintering of TiO2 and Ag with Pt heat treatment and dyeing being dealt with elsewhere [6,7].
Figure 1. Typical manufacturing scheme for a dye-sensitized solar cell and a
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