Researchers at UNIST in Korea may have overcome the problem of carbon-based electrocatalysts for dye-sensitized solar cells with their new catalyst made from edge-selenated graphene nanoplatelets.

DSSCs consist of a dye-coated titanium oxide photoanode, an electrolyte and a counter electrode (CE). Currently, the most widely used electrolytes in DSSCs are iodide/triode ones, and the most common CE is an optically transparent thin film of platinum (Pt) nanoparticles on fluorine-doped tin oxide (Pt-FTO). While Pt-based materials are among the most efficient CEs, Pt is an expensive precious metal that is in short supply. That is why researchers are constantly looking for alternative CE materials and the best candidates so far appear to be carbon-based. Such materials include carbon nanotubes, porous carbon, carbon spheres, active carbon and graphene. A major problem, however, with carbon-based CEs is that they are active enough in Co(II)/Co(III) electrolytes (and have a high PCE, here), but not sufficiently so in I-/I3- electrolytes.

The UNIST team has now made a new edge-selenated graphene nanoplatelet (SeGnP) CE material that has a better overall PCE and electrocatalytic performance in both electrolytes compared to Pt-based CEs. The researchers prepared their SeGnPs by mixing graphite and selenium powders together using high-velocity stainless steel balls in a planetary ball mill reactor. “The kinetic energy generated by the balls unzips graphitic C-C bonds and cracks Se-Se bonds,” explains the team. “Activated C and Se atoms can then form covalent C=Se and C-Se-C bonds along the broken edges of SeGnP.” They characterized the SeGnPs produced using various techniques, including atomic resolution transmission electron microscopy (AR-TEM).

While it is relatively known that functionalized graphene can effectively catalyze the iodide redox mediator with performance similar to that of platinum, this work has shown quite clearly the significant importance of graphene as a catalyst. The team hopes that the new catalyst "will inspire researchers to make other Pt-free CE materials, which may help to push forward practical applications of DSSCs".

The group will now be looking into different porous carbon-based materials, such as metalloids and light non-metal heteroatom-doped graphene nanoplatelets, to use as counter-electrodes in dye-sensitised solar cells.