Paper/graphene sandwich yields cheap, disposable flexible displays
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 four seconds while the de-intercalation cycle (going back to dark) takes under 0.5 s, which suggests such displays would mostly be suited to signage applications where content is not refreshed too frequently.
printing halftone color 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 4 V, 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 color patterns on the paper substrate prior to applying the MLG film, so as to reveal color when the electrodes turn transparent.
They also demonstrated a 5×5 multipixel paper display using a cross bar structure. The back and front graphene electrode strips, 5 mm wide and 25 mm long, yield square addressable pixels each 5×5 mm in size. By applying various bias voltage of 0, 2, and −2 V to the rows and columns, they could control the color of the intersecting area, again turning it from metallic to paper-view. The display remained operational upon being folded or even creased.
A limitation though, is the oxidization of the doped graphene layers, but the researchers are confident that coating the surface with a thin polymer layer could drastically improve the durability of such a display. Next, Kocabas’ team went to port their manufacturing method to a roll-to-roll compatible process, transferring multilayer graphene films onto A4-size printing paper.
As the researchers conclude in their paper, cutting, folding, and printing are common processes in the printing industry, which could take this novel paper-display approach to their advantage to design cheap reconfigurable displays with unique 3D shapes and colors.
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