The technology behind these new and exciting advances involves C60 Nanorods and Inorganic Photodoping[ii] and was developed by researchers at University of Surrey. One dimensional single-crystal nanorods of C60 possess unique optoelectric properties which makes them perfect for use in manufacturing low-cost large-area flexible photoconductor devices. Researchers were able to enhance the photosensitivity of the C60 nanorods by using a very low photodoping mechanism. Photodoping is used to solve a naturally occurring problem. When a C60 nanorod photoconductor device is irradiated with photons most of the excited electrons are concentrated in trap states rather than being available to contribute to the photocurrent as a whole, which reduces the responsivity and decreases the photosensitivity overall. To counteract this and to improve the photo-oxidation stability and extend the sensitivity of the device, researchers then introduced a photodopant. This fills the traps that naturally occur when C60 suffers degradation. These photodopants must form a type-II heterojunction so that when the composite is photoexcited the photodopants provide the additional electrons needed to fill the C60 traps states. This encourages the photosensitivity needed to detect the full spectrum of light.
Typically when photodopant devices are introduced the donor to acceptor ratio is very high and the devices rely primarily on the absorption and conductivity of the donor material. In this case in order to achieve the photosensitivity required for the use of these light sensors in a medical setting, the photodopants introduced enhance the photosensitivity of the acceptor material (i.e. the C60 nanorods) and not the donor material. To validate that the photodoped C60 nanorods truly experienced an enhancement of photosensitivity, the research team University of Surrey compared the responsivity spectrum of all the photodoped devices to that of an undoped C60 nanorod device. When the tests were done and comparisons were read results showed that responsivity was increased in the photodoped devices by up to two orders of magnitude. This reinforced the idea that via an ultralow doping mechanism and careful selection of dopants and photodopants, both mobility and the photoconductivity of such a trap rich molecular organic semiconductor can be enhanced by many orders of magnitude.
While this technology may not be implemented and readily available to all within the next year, chances are that within the next decade these light sensors could be a standard part of all medical practices’. This could conceivably greatly enhance preventative care and drive down costs of major procedures. It also has major implications for security and military personnel as well. It is appropriate to note that without the availability of semiconductor processing this technology would never have been plausible.
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[i] University of Surrey. (2014, May 23). New sensor could light the way forward in low-cost medical imaging. ScienceDaily. Retrieved May 23, 2014 from www.sciencedaily.com/releases/2014/05/140523082928.htm
[ii] Rinku Saran, Vlad Stolojan, Richard J. Curry. (23 May 2014). Ultrahigh Performance C60 Nanorod Large Area Flexible Photoconductor Devices via Ultralow Organic and Inorganic Photodoping. Scientific Reports, 2014; 4 DOI: 10.1038/srep05041