As mentioned in the introduction, nc-DSCs are expected in the short term to be available for low-power applications, competing with other thin film technologies, among which amorphous silicon is already an established technology.
One aspect of indoor applications which makes sealing somewhat less critical is the low temperature range under operation and storage, as well as the possibility of using electrolytes with high viscosity and high boiling point. For commercialisation of indoor dye devices, it is of the utmost importance to simplify and optimize the currently known process steps.
In the above-mentioned European project , a number of partners have investigated every aspect of the production and testing of nc-DSC for indoor applications. The goal of the project was to design a production line for indoor modules and to calculate the total cost. It was concluded that, among the various possible fabrication concepts, production of the monolithic concept described in Sect. 7.3.2 is in principle the most attractive for industrial production of Dye Indoor PV modules. A large part of the activity focused on processing large batches of mini-modules, for which the individual process steps have already been mentioned in Sect. 7.3.2.
Fig. 7.6. (a) Standard screen-printing equipment, (b) Master plates leaving the in-line drying furnace after screen-printing, (c) Master plates after sintering in a batch oven
Since modules are prepared with several elements in series, the TCO on the glass substrate must be structured in thin lines in order to separate individual elements. Therefore, cleaned Sn02:F master plates with a size of 10 x 10 cm2 are structured using a Nd:YAG laser. Three layers are subsequently deposited on the TCO plate using standard screen-printing equipment in a clean room environment (Fig. 7.6a). Three different screen-print pastes have been developed for the monolithic cell design, containing ТІО2, zirconium dioxide, and carbon black, respectively, as well as organic me – dia/binders.
After each printing step, the master plates are dried using an in-line IR belt furnace (Fig. 7.6b). This involves levelling the layers, evaporating the paste solvent and then substantially shrinking the layers. After the drying step, the layers are fired at 450°C in a batch oven to burn out organic residuals (Fig. 7.6c). These processing steps are carried out with commercially available materials and equipment, e. g., laser structuring, screen-printing, and standard drying and sintering ovens.
Further process steps such as dye coloration, electrolyte filling and seal – ing/lamination, leading to sealed completed modules, have also been carried out on 10 x 10 cm2 substrates. For these process steps, dedicated equipment has been developed from the laboratory stage, since it is not commercially available. A photo of a fully processed master plate is shown in Fig. 7.7. It contains 4 modules of 5 cells each (total area of 1 module 20 cm2) on one TCO plate of 100 cm2. These modules were intended for LCD powered price tags on supermarket shelves.
The five-cell dye module with the design showed in Fig. 7.7 was compared with a commercially available amorphous Si module (for price tag application) and similar performance was demonstrated for the active module area. The I-V parameters are shown in Table 7.1.
Table 7.1. Comparison between I-V parameters of an amorphous silicon module and a five-cell dye module
Fig. 7.7. Fully processed master plate (10 x 10 cm2), containing 4 mini-modules. The dye used is N719 [Ru(NCS)2(2,2′-bipyridyl-4,4,-dicarboxylate)2]- A molten salt, hexylmethylimidazolium iodide (HMII) containing 10 mM І2, was used as the electrolyte