Stabilization of metal counter electrodes for dye solar cells

Abstract

The purpose of this study was to identify stable metal based counter electrodes (CE) for dye solar cells (DSC). Previous studies have shown that stainless steel (StS 304) suffers from corrosion when used as a counter electrode. Therefore metals which have inherently higher corrosion resistance, such as stainless steel types 321, 316 and 316L, Inconel 600 and titanium, were investigated here. When using thermal platinization for the preparation of the catalyst layer on CE, only the titanium foil based metal based DSC remained consistently stable in the 1000 h light soaking test. The counter electrodes were also prepared with sputtering ~20 nm thick layer of Pt which provides a highly uniform layer on the CE which acts also as a protective coating on the metal. With sputtered Pt, DSC on all studied metals expect for Inconel remained at 80-95 % of the initial efficiency after light soaking test for 1000 h.

Do Counter Electrodes on Metal Substrates Work with Cobalt Complex Based Electrolyte in Dye Sensitized Solar Cells?

“…Although not all metals were stable in the cobalt electrolyte, it can be said that the cobalt electrolyte was in fact less aggressive than the iodine ones (relative to the reference cells on glass): In our recent study a cell with StS 304 as the counter electrode substrate degraded fully within 24 hours with an iodine based electrolyte, 8 whereas here it was as stable as the glass for the entire study period (500 h). Literature also shows that Cu degrades in the iodine electrolyte in a few seconds (the electrolyte changes color as it is being filled to the cells) 5 whereas here with cobalt it took longer (tens of minutes) for the visible changes to appear.…”

“…In 19 previous studies with StS based electrodes in iodine electrolyte, the low temperature treatments have resulted in a higher catalytic activity compared to thermal platinization in contrast to the case of glass based electrodes. 4,8 This feature is assumed to be a result of higher contact resistance between the metal and the catalyst layer caused by the growth of an oxide layer between them in the heat treatment. Unrelated to the actual electrocatalytic activity of the catalyst particles themselves, this would affect both cobalt and iodide based cells, as found in the experiments.…”

“…8 A corrosion blocking layer such as a sputtered Pt layer can improve the stability in the case of many metals, but even that is not sufficient if the metal is highly prone towards corrosion. 8 In particular the cheap metals are often prone to corrosion and to enable their use without costly coatings, a non-aggressive electrolyte is needed. One approach is to change the redox couple.…”

“…Many of them have been suggested for dye solar cells earlier to be used with iodine based electrolyte. [3][4][5][6][7][8] Earlier studies have also…”

Low Cost Ferritic Stainless Steel in Dye Sensitized Solar Cells with Cobalt Complex Electrolyte

“…on the other electrode). [4][5][6] Here, the SEM images did not reveal any marks of corrosion in the surface of the aged ferritic steel as the example in Figure 7 shows. Furthermore, the elemental analysis combined to SEM imaging did not show any apparent corrosion products at the other electrode (i.e.…”