I. Introduction
There has been an increasing demand for sustainable and clean energy resources due to the depletion of fossil fuels [1]. Reduction of CO2 emissions and utilization of renewable energy sources are the only hope to solve the global warming issues [2], [3]. Especially, photovoltaic technology is much attractive because of its eco-friendly nature. Among the various photovoltaic dye-sensitized solar cells (DSSCs) explored so far, DSSC is one of the frontier areas of research in energy conversion [4], [5]. After seminal work of O'regan and Gratzel [6], DSSC became a key area of research for researchers all over the world. The low fabrication cost, ease of fabrication, and comparable power conversion efficiencies (PCEs) make DSSC a potential alternative for conventional silicon solar cells [7]. A typical DSSC comprises four key components—namely, photoanode (mostly TiO2 or ZnO), counter electrode (platinum), dye (ruthenium-based dyes), redox electrolyte (iodide/tri-iodide). The PCE of DSSC depends largely on the choice of materials used in the components such as photoanode and counter electrode. Therefore, it is very crucial to choose suitable materials in order to prepare the components for DSSC to achieve greater PCE. In this regard, titania aerogels, a promising photoanode material, were used as it provides highly interconnected 3-D structures including large pores and high surface area [8]. These properties of titania aerogel help to increase the PCE of DSSC, because the dye uptake is high and allows easy penetration to electrolytes [9], [10]. Recently, our group developed titania aerogel-based QS-DSSC and achieved a power conversion efficiency above 5% [11]. However, the use of platinum counter electrode makes the fabrication expensive. Therefore, in order to reduce the fabrication cost, there is a necessity to choose suitable counter electrode materials. The previous reports suggest that many carbon sources, such as graphite [12]–[17], carbon nanotubes [18]–[21], and nanofibers [22], were used as efficient counter electrode materials for DSSC applications. Especially, graphite received great attention of researchers because of its low cost, natural abundance, and interesting electrical and mechanical properties [14], [23]. In addition to this, graphite can be composited with metal oxide to use as photoanode [24]–[27] or as pristine graphite for counter electrode of DSSC with better performance, enhanced DSSC stability [12], [18], [28], [29].