DOI: 10.1002/ijch.201400213 Recent Progress on Reduced Graphene Oxide-Based Counter Electrodes for Cost-Effective Dye-Sensitized Solar Cells Suresh Kannan Balasingam [a] and Yongseok Jun* [b] 1. Introduction Since modern society relies entirely on an energy-based economy, the existing fossil fuel reserves are expected to run out in a few decades, causing future generations to face a severe energy crisis. Moreover, the existing fossil fuel-based energy technologies emit greenhouse gases, which have a great impact on the environment, including what is known as global warming. [1] To solve these two key issues, alternative energy conversion systems that could solely depend on renewable energy resources (e.g., solar, wind, tidal, or geothermal energy) need to be de- veloped. Of these, solar cells are one of the prominent energy conversion devices, in which the direct conversion of solar to electrical energy could be feasible. In addition, the sun supplies an abundant amount of solar energy throughout the day, indicating that this energy source is unlimited. The solar cell technology currently available on the market is based on first- and second-generation solar cells (e.g., silicon, CdTe, and copper indium gallium [di]selenide solar cells) that have the merits of high effi- ciency and long-term stability. However, the cost of these modules is very high, which prevents this technology from reaching widespread clients. To reduce the cost of solar cells, third-generation solar cells have been under progressive research for the past few decades. [2] Dye-sen- sitized solar cells (DSSCs) are one type of third-genera- tion solar cells that has attracted many researchers be- cause of their numerous merits, including the following: low cost, ease of fabrication, variety of colors, and high power conversion efficiency (PCE). [3] Recent literature on DSSCs reported a maximum efficiency of around 13 %, which revealed that the technology is commercially viable if we could reduce the cost of the solar cell compo- nents. [4] DSSCs are composed of dye-coated mesoporous TiO 2 on fluorine-doped tin oxide (FTO)-coated glass as a working electrode, an iodine-based electrolyte, and a thin Pt layer coated on FTO-coated glass as a CE. The two most expensive components are the FTO-coated glass substrate and Pt-coated CE. Substitution of the FTO-coated glass substrate with various metal substrates either on the working or counter electrode part could cer- tainly reduce the cost of the DSSCs. This possibility was briefly discussed in our previous feature article. [5] Anoth- er approach is to replace the noble Pt metal-based CEs with carbonaceous materials and/or non-noble metal oxide/chalcogenide-based composite catalysts, which have been briefly described in previous review articles. [6] Of Abstract : Dye-sensitized solar cells (DSSCs) are one type of highly efficient low-cost solar cells among third-generation photovoltaic devices. Replacing the expensive components of DSSCs with alternative inexpensive and earth-abundant materials would further reduce their price in the solar cell market. Recently, graphene-based low-cost counter electro- des (CEs) have been developed, which could serve as a po- tential alternative to the expensive platinum-based CEs. In this review article, we have summarized recent research on various reduced graphene oxide (rGO)-based composite CE materials, methods for their synthesis, their catalytic activity, and the effective utilization of such CEs in DSSCs. The pho- tovoltaic performance of DSSCs made of rGO-based compo- site CEs were compared with the reference Pt-based cells, and the photovoltaic parameters are summarized in tables. Keywords: composites · counter electrodes · catalysis · reduced graphene oxide · dye-sensitized solar cells [a] S. K. Balasingam Department of Chemistry School of Natural Science Ulsan National Institute of Science and Technology (UNIST) Ulsan 689-798 (Republic of Korea) [b] Y. Jun Department of Materials Chemistry and Engineering Konkuk University Seoul 143-701 (Republic of Korea) Tel: (+ 82) 2-450-0440 e-mail: yjun@konkuk.ac.kr Isr. J. Chem. 2015, 55, 955 – 965 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 955 Review