Photonic synapses combine sensing and processing in a single device, so they are promising candidates to emulate visual perception of a biological retina. However, photonic synapses with wavelength selectivity, which is a key property for visual perception, have not been developed so far. Herein, organic photonic synapses that selectively detect UV rays and process various optical stimuli are presented. The photonic synapses use carbon nitride (C3 N4 ) as an UV-responsive floating-gate layer in transistor geometry. C3 N4 nanodots dominantly absorb UV light; this trait is the basis of UV selectivity in these photonic synapses. The presented devices consume only 18.06 fJ per synaptic event, which is comparable to the energy consumption of biological synapses. Furthermore, in situ modulation of exposure to UV light is demonstrated by integrating the devices with UV transmittance modulators. These smart systems can be further developed to combine detection and dose-calculation to determine how and when to decrease UV transmittance for preventive health care.

/pdf/retina-inspired-carbon-nitride-based-photonic-synapses-for-4vkoa89ook.pdf

Retina-Inspired Carbon Nitride-Based Photonic Synapses for Selective Detection of UV Light.

Significant advances have been made recently in the area of organic electronics and optoelectronics based on small molecules as a result of the synthesis of new soluble and air-stable molecules. First reported 20 years ago, organic transistors quickly became a focus of intense research and development in academic and industrial laboratories. The great progress achieved thus far offers an opportunity for the production of new small electro-active molecules and the implementation of low-cost device fabrication technologies. This review focuses on recently synthesized p- or n-type organic semiconductors, particularly those suitable for fabrication of solution-processed and/or air-stable field effect transistors with an emphasis on low-cost wet processes. The numerous recent efforts realized in optoelectronics, particularly on phototransistors based on small molecules, offer various opportunities in applications for such organic compounds. Copyright © 2011 Society of Chemical Industry

Organic transistors and phototransistors based on small molecules

We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants’ radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

Thermoelectric Properties of Indium and Gallium Dually Doped ZnO Thin Films

Au cours de cette synthese destinee a mon Habilitation a Diriger des Recherches, je dresse dans un premier temps le bilan de mes contributions menees sur la periode 2005-2014 et centrees sur l’etude de systemes hybrides organiques/inorganiques varies pour l’optique non lineaire et l’optoelectronique. En particulier, j’aborderai les specificites des materiaux inorganiques nanostructures, puis celles des materiaux organiques -conjugues, avant d’illustrer les phenomenes physiques originaux decoulant de leur association. Les developpements effectues depuis ma nomination au sein de l’Institut XLIM (UMR 7252, Universite de Limoges/CNRS) en 2007 illustreront plus directement mon implication dans le domaine de la conversion photovoltaique de l’energie, avec notamment un travail particulier dedie aux cellules solaires hybrides a l’etat solide, ainsi qu’aux composites polymeres semi-conducteurs / nano-objets. Fort de cette experience pluridisciplinaire dans le domaine des Nanotechnologies, de la caracterisation physique et optoelectronique, ainsi que des processus photo-physiques associes, je proposerai finalement des contributions a court terme et a plus long terme dans les domaines de la recuperation d’energie et des telecommunications optiques sans fils.

https://hal.archives-ouvertes.fr/tel-01132515/document

Composites Hybrides Organiques/Inorganiques Pour la Conversion de l'Énergie et l'Optoélectronique

Light- and bias-induced effects in pentacene-based thin film phototransistors with a photocurable polymer dielectric

Electronic transport and optical properties of thin oxide films

We report on the processing and characterization of organic photocouplers and phototransistors. These optoelectronic components were realized on the same transparent substrate by coupling an organic light emitting diode (OLED) with a photoconductive material such as pentacene. Various OLEDs with emission peaks in the green (550 nm) and the blue (450 nm) have been tested in order to optimize the photocoupler performance in terms of photocurrent gain ( I photocurrent / I dark ) and response times. In the first hand, we showed that the photocurrent gain increases as the wavelength decreases, and in the second hand, that the rise and decay times, corresponding, respectively to the illumination time of the component and to the time required for the device to come back to its initial state, are faster for photons of high energy: from a wavelength of 450 nm, the recombination processes are fast enough so that no photocurrent persists during relaxation. Moreover, we examined the performance of a phototransistor based on the coupling of an OLED (with an emission peak at 550 nm) as an input unit with a transistor (based on pentacene and polymethylmethacrylate as the dielectric gate) as an output unit. The characteristics of the transistor under illumination and at maximal luminance are consistent with a charge carrier mobility and a threshold voltage of about 0.03 cm 2  V −1  s −1 and 12.5 V, respectively.

Visible light effect on the performance of photocouplers/phototransistors based on pentacene

In this paper, the fabrication and characterisation of pentacene-based photoconductors using indium tin oxide electrodes obtained by ion beam sputtering are discussed. The photoelectric properties of pentacene under red (632 nm) and ultraviolet (365 nm) illuminations were investigated. We have shown that the photocurrent was dependent on the wavelength, bias voltage and illumination side of the device. Moreover, we have demonstrated with transparent electrodes that the top contact configuration yields better performance compared to the bottom contact configuration. We obtained a maximum photoconductivity gain of approximately 3 × 10 and a faster dynamic response when the photoconductor with top contact geometry was illuminated with ultraviolet light from the semiconductor side (top illumination), with a photoconductivity estimated at 10 cm.

/pdf/transparent-pentacene-based-photoconductor-high-3lbgs44qg0.pdf

Firas Hijazi

Papers

Electronic transport and optical properties of thin oxide films

Visible light effect on the performance of photocouplers/phototransistors based on pentacene

Transparent pentacene-based photoconductor: High photoconductivity effect

Transparent conductive ZnO thin films processed from solution: influence of doping on optical and electrical properties

Electronic transport and physical properties of metallic oxide films