Chapter Solution-Processed Graphene-Based Transparent Conductive Electrodes as Ideal ITO Alternatives for Organic Solar Cells

The isolation of free-standing graphene in 2004 was the spark for a new scientific revolution in the field of optoelectronics. Due to its extraordinary optoelectronic and mechanical properties, graphene is the next wonder material that could act as an ideal low-cost alternative material for the effective replacement of the expensive conventional materials used in organic optoelectronic applications. Indeed, the enhanced electrical conductivity of graphene combined with its high transparency in visible and near-infrared spectra, enabled graphene to be an ideal low-cost indium tin oxide (ITO) alternative in organic solar cells (OSCs). The prospects and future research trend in graphene-based TCE are also discussed. On the other hand, solution-processed graphene combines the unique optoelectrical properties of graphene with large area deposition and flexible substrates making it compatible with printing and coating technologies, such as roll-to-roll, inkjet, gravure, and flexographic printing manufacturing methods. This chapter provides an overview of the most recent research progress in the application of solution-processed graphene-based films as transparent conductive electrodes (TCEs) in OSCs. (a) Chemically converted graphene (CCG), (b) thermally and photochemically reduced graphene oxide, (c) composite reduced graphene oxide-carbon nanotubes, and (d) reduced graphene oxide mesh films have demonstrated their applicability in OSCs as transparent, conductive electrodes

Solution-Processed Graphene-Based Transparent Conductive Electrodes as Ideal ITO Alternatives for Organic Solar Cells

The isolation of free-standing graphene in 2004 was the spark for a new scientific revolution in the field of optoelectronics. Due to its extraordinary optoelectronic and mechanical properties, graphene is the next wonder material that could act as an ideal low-cost alternative material for the effective replacement of the expensive conventional materials used in organic optoelectronic applications. Indeed, the enhanced electrical conductivity of graphene combined with its high transparency in visible and near-infrared spectra, enabled graphene to be an ideal low-cost indium tin oxide (ITO) alternative in organic solar cells (OSCs). The prospects and future research trend in graphene-based TCE are also discussed. On the other hand, solution-processed graphene combines the unique optoelectrical properties of graphene with large area deposition and flexible substrates making it compatible with printing and coating technologies, such as roll-to-roll, inkjet, gravure, and flexographic printing manufacturing methods. This chapter provides an overview of the most recent research progress in the application of solution-processed graphene-based films as transparent conductive electrodes (TCEs) in OSCs. (a) Chemically converted graphene (CCG), (b) thermally and photochemically reduced graphene oxide, (c) composite reduced graphene oxide-carbon nanotubes, and (d) reduced graphene oxide mesh films have demonstrated their applicability in OSCs as transparent, conductive electrodes

Triplet excitations in carbon nanostructures

We show that the energy differences between the lowest optical singlet exciton and the lowest triplet exciton in semiconducting single-walled carbon nanotubes with diameter $\sim 1$ nm and graphene nanoribbons with widths $\sim 2$ nm are an order of magnitude smaller than in the $\pi$-conjugated polymer poly(para-phenylenevinylene). Our calculated energy gaps between the singlet and triplet excitons are in excellent agreement with the measured values in three different nanotubes with diameters close to 1 nm. The spatial extent of the triplet exciton is nearly the same as that of the singlet exciton in wide nanotubes and nanoribbons, in contrast to that in $\pi$-conjugated polymers, in which the triplet exciton exhibits strong spatial confinement. Weakly confined behavior of the triplet state begins in nanoribbons with widths as narrow as 2.5 times the graphene unit lattice vector. We discuss possible consequences of the small singlet-triplet energy difference in the carbon nanostructures on device applications.Comment: 9 pages, 2 tables, 4 figure

Monitoring Charge Exchange in P3HT-Nanotube Composites Using Optical and Electrical Characterisation

Charge exchange at the bulk heterojunctions of composites made by mixing single wall nanotubes (SWNTs) and polymers show potential for use in optoelectronic devices such as solar cells and optical sensors. The density/total area of these heterojunctions is expected to increase with increasing SWNT concentration but the efficiency of solar cell peaks at low SWNT concentrations. Most researchers use current–voltage measurements to determine the evolution of the SWNT percolation network and optical absorption measurements to monitor the spectral response of the composites. However, these methods do not provide a detailed account of carrier transport at the concentrations of interest; i.e., near or below the percolation threshold. In this article, we show that capacitance–voltage (C–V) response of (metal)-(oxide)-(semiconducting composite) devices can be used to fill this gap in studying bulk heterojunctions. In an approach where we combine optical absorption methods withC–Vmeasurements we can acquire a unified optoelectronic response from P3HT-SWNT composites. This methodology can become an important tool for optoelectronic device optimization