Comprehensive review of carbon materials as counter electrodes in dye-sensitized solar cells: Efficiency assessment and deposition methods

Due to their minimal material cost, simple fabrication procedures and eco-friendly nature, dye-sensitized solar cells (DSSCs) are a potential low-cost substitute for traditional silicon based solar cells. They are composed of several components, and each one has a distinct operation, such as titanium dioxide (TiO2) a porous semi-conductor works as the photoanode, platinum/carbon/composite/conductive polymer-based materials as the counter electrode (CE), and natural/synthetic/organic-based sensitized dye as a sensitizer with the electrolyte as the electron transfer bridge. Research is being conducted on each of its components; some are optimized to a certain extent, while others continue to stimulate attention. Normally, platinum (Pt) is used as the CE for higher efficiency but due to its cost, several studies are taking place for cost-effective alternatives since the CE has recently been on the radar for large-scale production. Lately, various conductive and electro-catalytically active materials have been used as the CE including Pt, carbon black, mesoporous carbon, graphite, graphene, carbon nanotubes, metals, composites and conducting polymers. Moreover, not only do these materials have an influence on the performance but the deposition method also determines the energy conversion efficiency, stability, and performance of the overall cell, so the deposition method is all very critical in the construction of the cell. This review analysis covers (a) the fundamentals of DSSCs, (b) deposition techniques for both photo and counter electrode, (c) deposition methods exclusively for counter electrode, (d) various carbonaceous materials used as alternatives to Pt, and (e) conductive polymers as counter electrodes.