Graphene based photoanode for DSSCs with high performances

Catalytic Effect of 1,4-Dioxane on the Kinetics of the Oxidation of Iodide by Dicyanobis(bipyridine)iron(III) in Water

Dye-sensitized solar cells (DSSCs) are a technically and financially viable alternative to today’s photovoltaic systems using p-n junctions. The two functions are isolated here, which are unlike traditional systems where the semiconductor is thought to perform both light absorption and charge carrier transport. This article discusses the potential use of dicyanobis(bipyridine)iron(III) to oxidize iodide as a sensitizer in DSSCs. However, it is critical to understand the kinetics of this essential process in order to understand the mechanism of electron transport. The oxidation of iodide by dicyanobis(bipyridine)iron(III) in three reaction media was studied: water, 10% v/v 1,4-dioxane-water, and 20% v/v 1,4-dioxane-water. The reaction was carried out in a regular laboratory setting, with no special sensitive conditions or the use of expensive materials, making it a cost-effective and practical method. Dicyanobis(bipyridine)iron(III) oxidized iodide in selected media at 0.06 M ionic strength and constant temperature. The reaction was subjected to a spectrophotometric analysis. The data were acquired by measuring the rise in visible absorbance as a function of time after the formation of dicyanobis(bipyridine)iron(II). The reaction proceeded with an overall fractional (0.5), first order, and third order in water, 10% media, and 20% media, respectively. The presence of dicyanobis(bipyridine)iron(III) in either of the reaction media had no effect on the rate. The effect of protons (H+) on the rate constant indicated resistance in water and catalysis in dioxane-water media containing 10–20% dioxane. When the ionic strength was raised, there was no change in the rate constant in water, but there was a deceleration in both binary solvent media. In an aqueous medium, the thermodynamic parameters of activation were computed as Ea 46.23 kJ mol−1, 24.62 M s−1, ΔH# 43.76 kJ mol−1, ΔS# −226.5 J mol−1 K−1, and ΔG# 111.26 kJ mol−1 (25 °C). By increasing the rate of the reaction to its maximum, this study discovered the binary solvent media with the highest catalytic efficiency, i.e., 20% v/v 1,4-dioxane-water, which may increase the efficiency of DSSCs without using any expensive material or unusual experimental conditions.

Recent advances in graphene-based materials for dye-sensitized solar cell fabrication

In the past few years, dye-sensitized solar cells (DSSCs) have received considerable research attention, as potential alternatives to the commonly used, but expensive, silicon-based solar cells owing to the low-cost, facile fabrication procedures, less impact on the environment, capability of working even under low incoming light levels, and flexibility of DSSCs. However, the relatively low power conversion efficiencies (PCEs) and poor long-term operational stability of DSSCs still limit their large-scale and commercial applications. As a consequence, this has prompted tremendous research effort towards the realization of high performance and sustainable devices, through tailoring of the properties of the various DSSC components, via approaches such as introducing novel materials and new synthesis techniques. Among these, the application of novel materials, especially carbon-based materials, such as graphene and its derivatives, is more appealing due to their excellent optoelectronic, mechanical, thermal and chemical properties, which give them ample potential to replace or modify the traditional materials that are commonly used in the fabrication of the various DSSC components. In addition, the low-cost, abundance, non-toxicity, large specific surface area, flexibility and superior stability of graphene-based materials have enabled their recent use as photoanodes, i.e., transparent conducting electrodes, semiconducting layers and dye-sensitizers, electrolytes and counter electrodes in DSSCs. Recently, the introduction of graphene-based materials into DSSCs resulted in a pronounced increase in PCE from ∼0.13 to above 12.00%. Thus, employing the recent breakthroughs can further improve the optoelectronic properties of the various DSSC components and, hence, close the gap between DSSCs and their silicon-based counterparts that are currently exhibiting desirable PCEs of above 26%. Therefore, this review focuses on the recent applications of graphene-based materials as photoanodes, electrolytes and counter electrodes, for the possible fabrication of all-carbon-based DSSCs. The limitations, merits and future prospects of graphene-based DSSCs are discussed, so as to improve their photovoltaic performance, sustainability and cost-effectiveness.

Influence of Sputtering Temperature of TiO2 Deposited onto Reduced Graphene Oxide Nanosheet as Efficient Photoanodes in Dye-Sensitized Solar Cells

Renewable solar energy is the key target to reduce fossil fuel consumption, minimize global warming issues, and indirectly minimizes erratic weather patterns. Herein, the authors synthesized an ultrathin reduced graphene oxide (rGO) nanosheet with ~47 nm via an improved Hummer's method. The TiO2 was deposited by RF sputtering onto an rGO nanosheet with a variation of temperature to enhance the photogenerated electron or charge carrier mobility transport for the photoanode component. The morphology, topologies, element composition, crystallinity as well as dye-sensitized solar cells' (DSSCs) performance were determined accordingly. Based on the results, FTIR spectra revealed presence of Ti-O-C bonds in every rGO-TiO2 nanocomposite samples at 800 cm-1. Besides, XRD revealed that a broad peak of anatase TiO2 was detected at ~25.4° after incorporation with the rGO. Furthermore, it was discovered that sputtering temperature of 120 °C created a desired power conversion energy (PCE) of 7.27% based on the J-V plot. Further increase of the sputtering temperature to 160 °C and 200 °C led to excessive TiO2 growth on the rGO nanosheet, thus resulting in undesirable charge recombination formed at the photoanode in the DSSC device.

Three-dimensional graphene networks and RGO-based counter electrode for DSSCs

Graphene is considered to be a potential replacement for the traditional Pt counter electrode (CE) in dye-sensitized solar cells (DSSCs). Besides a high electron transport ability, a close contact between the CE and electrolyte is crucial to its outstanding catalytic activity for the I3 -/I redox reaction. In this study, reduced graphene oxide (RGO) and three-dimensional graphene networks (3DGNs) were used to fabricate the CE, and the graphene-based CE endowed the resulting DSSC with excellent photovoltaic performance features. The high quality and continuous structure of the 3DGNs provided a channel amenable to fast transport of electrons, while the RGO afforded a close contact at the interface between the graphene basal plane and electrolyte. The obtained energy conversion efficiency (η) was closely related to the mass fraction and reduction degree of the RGO that was used. Corresponding optimization yielded, for the DSSCs based on the 3DGN-RGO CE, a value of η as high as 9.79%, comparable to that of the device using a Pt CE and hence implying promising prospects for the as-prepared CE.

Selective adsorption and decomposition of pollutants using RGO-TiO2 with optimized surface functional groups

Reduced graphene oxide (RGO) samples with optimized types of surface functional groups were hybridized with TiO2 to achieve the selective adsorption and removal of various pollutants. A high ratio of hydroxyl groups was found to be remarkably advantageous for the adsorbtion and decomposition of rhodamine-B (and similar pollutants), while a high ratio of carboxyl groups was found to promote the ability to adsorb and decompose phenol. Moreover, the presence of carboxyl groups on the RGO edge provides a pre-condition to form a close chemical connection with TiO2, which has been proven by the obtained electron paramagnetic resonance (EPR) curve, infrared spectroscopy (IR) and electron lifetime. The resulting composite photocatalysts display excellent photocatalytic activities under both UV- and visible-light illumination, indicating that the well-designed surface micro-circumstances of the RGO are quite significant.