Self-powered transparent paper promises new wave of ‘smart transparent paper electronics’
Thu 16 Jul 2015
International researchers recently presented a report [PDF paywalled] promising the advent of paper that generates power natively, with the initial scope of developing systems to prevent forgery and prevent the theft of valuable paintings – but the research suggests far wider possibilities, since the paper construct contains a latent charge not dependent on energy input from users, nor from bacteria and ‘dirty water’.
The paper – entitled ‘Self-Powered Human-Interactive Transparent Nanopaper Systems’ – was presented at the online edition of ACS Nano, with the team led by Prof. Jun Zhou from the Wuhan National Laboratory for Optoelectronics, and School of Optical and Electronic Information, together with Ass.Prof. Liangbing Hu from the University of Maryland’s Department of Materials Science and Engineering & Energy Research Center.
The paper utilises electret materials – derived from ‘electricity’ and ‘magnet’ – which are able to retain residual charges in a manner similar to the more familiarly understood magnet. Electret technology is not new, and was being used in microphones and other solid state devices as early as 1960 [Wayback]. But the research group’s Transparent Paper-Based Flexible Generator (TPFG) incorporates carbon nanotubes (CNTs) to facilitate the residual charge in an end-product that is in every way more flexible – and clear.
The TPFG comprises two electrode components in the form of two transparent sheets of Nanopaper overlaid with a film of CNTs, with one of the sheets also coated in 30µm polyethylene (PE) film which contributes the cardinal non-fluorine electret. When the coated aspects are joined their retaining charges output electrostatic induction effects which provide the power.
Commenting on the design Prof. Zhou explained “The variation of the air gap between the two components has a key role in the generation of the alternating electric currents…When the TPFG is in the original – equilibrium – state, no free electrons will flow in the external circuit. However, when a vertical compression is applied to the TPFG, the air gap becomes smaller and more positive charges will be induced in the bottom CNT electrode. As a result, the equilibrium state is broken and current will flow from the top CNT electrode to the bottom CNT electrode,”
The team are continuing their research with a view to improving long-term stability. No mention is made of the duration of practical power output – or the point at which the paper will become ‘flat’ in every sense – nor of the possibilities of ‘recharging’ transparent self-powered paper, if the customary wear and tear it might be expected to receive don’t potentially make the point moot. The TPFG is noted to perform less efficiently in humid environments, and in its current state is not suitable for configurations that put it in contact with skin, prompting Prof. Zhou and associates to consider alternative electret materials such as conductive polymers and silver nanowires.
The research team has developed prototype (art) anti-theft and anti-fake systems based on TPFG technology.
In 2013 Disney research into paper that generates energy from touching, rubbing and sliding garnered media attention, whilst a foldable paper battery powered by bacteria and ‘dirty water’ was proposed by engineer Seokheun Choi of Binghamton University in June. Transparent plastic substrates are also making new headway in the fields of RFID manufacture [PDF] and photovoltaic (solar powered) cells [PDF].