Wearable light emitting transistors for future communication devices

Nowadays, display and communication devices are supplementary items, many times posing transportation problems to the user, due to volume, weight and size, making them uncomfortable and inconvenient to use and carry. Current technology and innovation efforts look for alternative substrates, materials and ideas that eliminate or reduce much of these inconveniences. Products have been developed not only with reduced size and weight, but also improved flexibility. These products, including e-readers or rollable displays mimic more traditional forms of displaying information such as the information printed on paper. However, all of these applications are far from being fully integrated in basic objects of our society.

This proposal seeks to establish a new ground-breaking technology for flexible, transparent, comfortable and easy to carry textile-embedded communication devices. The approach to realize this aim is to build the first fibre-embedded device with controllable light emission: a light-emitting transistor completely entrenched in a fabric. This will be achieved by combining organic semiconductors and dielectrics with graphene as conductive layer, in a novel concept that merges flexibility, transparency, optoelectronic properties and fabrication compatibility of these materials with textiles.

Graphene and organic semiconductors combine mechanical flexibility and optical transparency with excellent electronic characteristics and low-temperature processing and are ideal for non-conventional substrates such as fibres of textiles. With just 3-4 Å thickness, monolayer graphene not only ensures high transparency, but it is bendable and stretchable. Together with its robustness and high conductivity, it is an extremely good candidate to replace current metallic electrodes. Polymers and organic small molecules, on the other hand, present a wide range of electrical behaviour, from conductors to insulators, with the possibility of solution processing. Several families of organic compounds present semiconductor behaviour and are successfully used in organic field-effect-transistors. Another advantage of organic materials is the possibility of chemical modification to add functionalities or change mechanical and optoelectronic properties. Such unique properties, allied with the potential that organic-semiconductor devices have demonstrated for display technology make it reasonable that a ground-break idea of wearable displays is achievable.

The outputs of the proposed project, the development of textile-embedded optoelectronic devices, will be fundamental to the development of smart textiles as well as of transparent and flexible electronics. Achieving this goal is of strategic importance to secure a leading role of UK in these research fields. The results of this research are also likely to be of wide use in consumer applications. For instance, the project will allow the development of completely new approaches for integrated electronics and forms of displaying information, capable to be embedded into our everyday clothing. Since textiles are so present in society, the ability to embed display-based information and communication devices into wearable textiles would transform our clothing into mobile phones, displays with electronic newspapers or GPS-activated maps, and would certainly facilitate interactions and exchanges between individuals and communities. Such devices represent a radical alternative to conventional technologies as they must bend, stretch, compress, twist and deform into complex shapes while maintaining their levels of performance and reliability. Establishing the foundations for this future in electronics is also essential for other societal needs, such as biomedical monitoring, communication tools for the sensory impaired people, and personal security.

Devices embedded into textiles, for simple, comfortable and handy transport could be used for display and communication devices, expanding social interactions. For instance, simple information display on clothes that could change colour for security alert, or display with informative tags in sport or social events could be attained. Furthermore, simple information like an address, maps or medicine alert to provide assistance to children or senior people could also be envisioned. The use of embedded discrete wearable devices would avoid loses and facilitate acceptance from the person who would wear it. More complex displays, combining communication technology could lead in the future to textile GPS or phones. Moreover, through the development of new fabrication techniques and innovative materials, this strategy could also be applied to other type of textile applications in the fields of health, security and energy harvesting. For example, in health care monitoring, fibre embedded light emitting devices can be used to integrate monitor displays that show and govern the usage of drug implants through a wireless communication system. Since textiles are a basic product in people's life, completely integrated devices could improve social care and inclusion, as well as opening new possibilities for health care. Wearable power sources that could use body heat and kinetic energy produced on movement as well as textile photovoltaics are also potential applications where technology developed by this project could be employed.

The outputs of our project, the development of graphene and organic materials based optoelectronic devices, will be fundamental to the development of transparent and flexible electronics. We have identified a number of areas that would potentially benefit from graphene and organic materials based transparent flexible devices. These include: photovoltaic devices, electronic circuits, sensors, detectors and displays. The ability to embed transparent graphene-based electronic circuits, sensors and detectors into windows in public areas is of great interest and would improve national security. Transparent devices have the potential to improve social welfare by transforming the windscreens of cars, trains and airplanes into display controls and GPS-activated maps. Transparent photovoltaic devices embedded in the windows in houses and offices will allow the production of electricity via solar energy. Graphene could be orders of magnitude cheaper than the indium tin oxide (ITO) electrodes and the silicon transistors currently used in vast numbers in many industrial sectors. The use of graphene in these devices opens up an entirely new avenue towards the development of efficient and economical transparent optoelectronics, thus fostering the economic competitiveness of the UK. Apart from their expense, today`s transparent devices, based on ITO, can create major recycling problems. Many other materials that are currently used in these devices, such as carbon nanotubes may be carcinogenic if they become airborne and are inhaled. The chances that graphene could be inhaled are very low since this material is a two-dimensional sheet which can be fabricated in large areas (100cmx100cm). Thus, by incorporating graphene in devices, the components of the future will not have negative effects on our health, will be much easier to recycle, and thereby will be environmentally more attractive.