The realization of optoelectronic devices on paper has been an outstanding challenge due to the large surface roughness and incompatible nature of paper with optical materials. In our brand new research, published in ACS Photonics (“Graphene enabled optoelectronics on paper“), we demonstrate a new class of optoelectronic devices on a piece of printing paper using graphene as an electrically reconfigurable optical medium. We reported a proof-of-concept ultra-thin electrochromic displays on a piece of paper and we anticipate that our results provide a significant step for realization of low-cost, disposable, and ubiquitous optoelectronics on unconventional substrates. Our aim is to convert the proposed device structure to a product level electronic paper by including the readout circuit and increase the resolution of the display by decreasing the individual cell size.
Optical properties of graphene can be controlled by doping. Doping alters the rate of interband and intraband electronic transitions of graphene and yields electro-modulation of optical absorbance in a very broad spectrum. Optical contrast achieved by atomically thin graphene is limited by the optical absorption of 2.3 percent, which is defined by fundamental constants. In our previous work (“Graphene Based Flexible Electrochromic Devices,” Scientific Reports 4, 6484 (2014)), we showed that multilayer graphene films yield high-contrast optically reconfigurable medium which is suitable for display applications on unconventional substrates. In our brand new research, by integrating a large area multilayer (ML) graphene on a piece of printing paper, we managed to fabricate optoelectronic devices on paper using electro-modulation of graphene layer via reversible intercalation process. The paper device consists of two multilayer graphene layers transfer-printed on both sides of the paper. In this configuration, ML-graphene simultaneously operates as the electrically reconfigurable optical medium and electrically conductive electrodes. In addition, the paper substrate yields a flexible and foldable mechanical support for the graphene layers and it holds the electrolyte (room temperature ionic liquid) in the network of hydrophilic cellulose fibers.
Fig. 1. Graphene on paper and the electrically controlled color change.
Electronic paper has been the most attractive application aiming to reconfigure the displayed information electronically on a sheet of printing paper. Paper-based substrates have been an ambition of research in various fields ranging from medical diagnosis to display technologies aiming to create low cost and ubiquitous devices. For example, paper-based microfluidic devices, electronic circuits, even robotic systems have been developed. In terms of display technology, several techniques have been developed based on electrophoretic motion of particles, thermochromic dye, electrowetting of liquids, to realize electronic paper (e-paper) that has great potential for consumer electronics. Contrasting the primary aim of e-paper, these technologies, however, are not compatible with conventional cellulose-based printing papers. With this motivation, using multilayer graphene as an electrically reconfigurable optical medium, we demonstrate an optoelectronic framework compatible with a conventional printing paper.
The key attributes of our devices are the simplicity of device architecture, high optical contrast, and broadband operation. Compatibility with roll-to-roll fabrication processes enables scalable approaches for large area applications such as e-paper. We illustrated the promises of the method by fabricating multi-pixel display devices on paper. With the advanced optical and mechanical properties of our graphene based devices We are expecting to contribute specifically to e-paper technology.
Since the paper is not compatible with the chemical fabrication steps due to its rough surface and physical instability, the main challenge is to develop alternative fabrication techniques devoted for the graphene-on-paper technology. We have already made a great progress on developing smart fabrication steps, however there are still some technical challenges to be solved about proper encapsulation.
Dr. Emre Ozan Polat is a post-doctoral researcher with ICFO — The Institute of Photonic Sciences in Barcelona, Spain. [email protected]
