Photoinduced Optical Transparency in Dye-Sensitized Solar Cells Containing Graphene Nanoribbons

Abstract

We describe the use of few-layer graphene nanoribbons, either attached to counter electrodes or dispersed into electrolyte, to induce optical transparency of an iodide/triiodide redox couple in a dye-sensitized solar cell (DSSC). We then evaluate the effect of reversible bleaching of the electrolyte on the DSSC performance. This bleaching effect is related to an energy transfer from photoexcited quantum-dot-like regions to the triiodide (I 3 À ) radical ions in the electrolyte, saturating their absorption in the visible optical range. DSSC power conversion efficiency using few-layer graphene nanoribbons at the counter electrode (5.8%) did not deteriorate when the electrolyte became optically transparent. The increased transparency of the electrolyte resulted in a decreased photocurrent density (from 17.6 to 14.2 mA/cm 2 ), an unchanged open circuit voltage of 750 mV, and a slightly increased fill factor (from 0.45 to 0.55). When the few-layer graphene nanoribbons were introduced into the electrolyte directly by ultrasonication, a semitransparent DSSC was found to have increased its power conversion efficiency in an optically inverted setup from 5.75% to 7.01%, arising from an increase in photocurrent from 9.9 to 12.1 mA/cm 2 . This significant photocurrent increase demonstrates that the effect of electrolyte bleaching can be used for further improving power conversion efficiency for inverted and tandem DSSCs, in which light has to pass through the electrolyte to generate photocurrent on one or more photocells.

One-step synthesis of graphene nanoribbon–MnO2 hybrids and their all-solid-state asymmetric supercapacitors

“…[12][13][14][15][16] Recently, several techniques have been explored to synthesize GNRs with reduced defects, such as chemical vapor deposition (CVD), 17 chemical, 18 lithographic, 19,20 and solution-based oxidative methods. 21,22 Compared with the graphene prepared from oxidized graphite, GNR has a characteristic geometry with widths varying from a few to several hundreds of nanometers and a length in the micrometer scale, which provides it with particular interest for the design and development of carbon-based nanomaterials or hybrids. 23,24 Due to their extraordinary electrical, optical, thermal, and mechanical properties resulting from their unique geometry, GNRs have been conveniently designed for various nanoscale device applications, such as supercapacitors, 25 photovoltaics 26 and eld effect transistors.…”

High temperature structural transformations of few layer graphene nanoribbons obtained by unzipping carbon nanotubes

“…6 The narrow graphene nanoribbons produced by oxidative unzipping are typically annealed prior to their use in devices 12,13 or electrodes. 14,15 While there are studies dealing with the evolution of functional groups on the reduced graphene nanoribbons showing them to be stable when annealed up to 800 C, 16 the morphological changes that the graphene nanoribbons undergo when annealed at higher temperatures are unknown, and it is the purpose of the present work to study these structural changes.…”

Influence of edge defects on Raman spectra of graphene

“…The quantitative ratio of oxygen and carbon atoms increases the D / G band intensity ratio [20]. Studies of nanoribbons from graphene oxide show that the ratio of these bands is higher than 1, which also confirms the effect by the shape of the sheet [21].…”