Paper and graphene sandwich yields cheap disposable displays

June 09, 2016 // By Julien Happich
By sandwiching a sheet of ordinary printing paper (impregnated with a ionic liquid electrolyte) between two films of multilayer graphene (MLG), researchers from the Bilkent University in Ankara, Turkey, were able to design reconfigurable and foldable paper displays, which they hope could find their way in cheap disposable applications.

The experiment stems from prior research performed by Prof. Coskun Kocabas' team, demonstrating that the reversible intercalation of ions into multilayer graphene (by applying a bias voltage), can modulates the optical absorption of these layers, turning them from dark metallic to transparent.

Contouring shape-specific electrodes in the MLG film and connecting them with silver-based conductive paint, the researchers simply used the multilayer graphene films as a high-contrast optically reconfigurable medium to turn on and off segments of the display. Under a bias voltage, the anions of the ionic liquid intercalate into the graphene layers and block the interband transitions in the visible spectrum, they wrote in a ACS Photonics paper "Graphene-Enabled Optoelectronics on Paper".

The intercalation cycle (going transparent) takes relatively long, about 4 seconds while the de-intercalation cycle (going back to dark) takes under 0.5s, which suggests such displays would mostly be suited to signage applications where content is not refreshed too frequently.

(left) the planar paper display showing a MLG electrode patterned using a plotter. (right) The number-shaped segment display in operation showing the isolated elements controlled individually.

A colour display could be formed by
printing halftone colour toner on the paper
prior to sandwiching it between the
MLG electrodes.

In their paper, the researchers detail several implementations operating with a bias voltage from 0 to 4V, some with pre-defined electrode patterns that would turn transparent and stand out from their dark metallic background. They also suggest the printing of matching colour patterns on the paper substrate prior to applying the MLG film, so as to reveal colour when the electrodes turn transparent.