Graphene‐Based Integrated Photovoltaic Energy Harvesting/Storage Device

Abstract

Energy scavenging has become a fundamental part of ubiquitous sensor networks. Of all the scavenging technologies, solar has the highest power density available. However, the energy source is erratic. Integrating energy conversion and storage devices is a viable route to obtain self-powered electronic systems which have long-term maintenance-free operation. In this work, we demonstrate an integrated-power-sheet, consisting of a string of series connected organic photovoltaic cells (OPCs) and graphene supercapacitors on a single substrate, using graphene as a common platform. This results in lighter and more flexible power packs. Graphene is used in different forms and qualities for different functions. Chemical vapor deposition grown high quality graphene is used as a transparent conductor, while solution exfoliated graphene pastes are used as supercapacitor electrodes. Solution-based coating techniques are used to deposit the separate components onto a single substrate, making the process compatible with roll-to-roll manufacture. Eight series connected OPCs based on poly(3-hexylthiophene)(P3HT):phenyl-C61-butyric acid methyl ester (PC60 BM) bulk-heterojunction cells with aluminum electrodes, resulting in a ≈5 V open-circuit voltage, provide the energy harvesting capability. Supercapacitors based on graphene ink with ≈2.5 mF cm(-2) capacitance provide the energy storage capability. The integrated-power-sheet with photovoltaic (PV) energy harvesting and storage functions had a mass of 0.35 g plus the substrate.

Adsorptive graphene doping: Effect of a polymer contaminant

“…We find that PMMA residues reduce the doping strength and facilitate degradation when HNO 3 and MoO 3 are employed, but induce a beneficial effect for AuCl 3 . Following vacuum annealing at elevated temperatures, AuCl 3 -doped graphene is up to five times more stable than the HNO 3 and MoO 3 counterparts.…”

“…Following HNO 3 or MoO 3 treatment, we find that the extent of polymer contamination induces a negative effect on the doping strength (Figs 1(a) to 1(d)). Primarily, the absolute sheet resistivity for heavilycontaminated graphene appears to be consistently higher than that for the sparsely-contaminated counterpart (Fig 1(a,c)), regardless of the fact that PMMA mildly p-dopes graphene.…”

“…[27] The presence of an additional shoulder at slightly lower wavenumber than the G peak is assigned to carbon contamination of the graphene layer. The fact this is absent in the spectra for HNO 3 and AuCl 3 dopants suggests that the doping process removes some contaminants from the graphene, whilst its presence in the spectra for MoO 3 dopant helps explain the highly unstable MoO 3 doping observed.…”

“…Herein, we assess the stability of HNO 3, MoO 3 , and AuCl 3 dopants upon transferred graphene with different extents of polymer contamination. Sheet resistivity measurements prove polymer residues induce a significant degenerative effect in terms of doping stability for HNO 3 and MoO 3 and a stabilizing effect for AuCl 3 . Further characterization by Raman spectroscopy and atomic force microscopy provides insight into the stability mechanism.…”

“…[1][2][3][4] For example, graphene has been proposed as a cheaper, flexible, and more sustainable alternative to indium tin oxide (ITO) for use in solar cells or touchscreen displays. [5] One such property is the very high carrier mobility afforded by graphene's unique band structure.…”