Visible light effect on the performance of photocouplers/phototransistors based on pentacene
15 Feb 2008-Materials Science and Engineering B-advanced Functional Solid-state Materials (Elsevier)-Vol. 147, pp 303-306
TL;DR: In this article, an organic light emitting diode (OLED) with a photoconductive material such as pentacene was used to optimize the photocoupler performance in terms of photocurrent gain and response times.
Abstract: 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.
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TL;DR: Organic photonic synapses that selectively detect UV rays and process various optical stimuli are presented and in situ modulation of exposure to UV light is demonstrated by integrating the devices with UV transmittance modulators.
Abstract: 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.
178 citations
TL;DR: In this paper, a review of 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, is presented.
Abstract: 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
96 citations
TL;DR: In this article, a pentacene-based thin film phototransistors were fabricated with a photocurable polymer insulator and their electrical stability was monitored when the devices were exposed to light sources at different wavelengths.
35 citations
TL;DR: In this paper, the authors have shown that using an optical excitation at a wavelength of 365nm photoconductivity modifies the carrier density without changing the mobility, and that there is no significant change in the mobility value when the transistor is bent in the direction of the current flow.
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References
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01 May 1992
TL;DR: In this article, the Shockley-Read one-center model and two-center recombination effects are discussed. But the model does not consider the effect of photo effects at grain boundaries.
Abstract: 1. Introductory concepts 2. Photoconductivity 3. One-center recombination models 4. The Shockley-Read one-center model 5. Two-center recombination effects 6. Recombination mechanisms 7. Steady-state photoelectronic analysis 8. Transient photoelectronic analysis 9. Photoeffects at grain boundaries 10. Amorphous semiconductors 11. Photovoltaic effects 12. Quantum wells and superlattices Bibliography Index.
542 citations
TL;DR: In this article, the photovoltaic effect in diode structures formed with thin films (100 nm) of the conjugated polymer poly(p-phenylene vinylene), PPV, sandwiched between electrodes of indium/tin oxide, ITO, and either aluminium, magnesium or calcium.
Abstract: We report measurements of the photovoltaic effect in diode structures formed with thin films (100 nm) of the conjugated polymer poly(p-phenylene vinylene), PPV, sandwiched between electrodes of indium/tin oxide, ITO, and either aluminium, magnesium or calcium. Under illumination incident through the ITO contact, large open-circuit voltages were measured, which saturated at approximately 1.2 V for Al and Mg devices, and approximately 1.7 V for Ca devices. Quantum efficiencies (short-circuit current/incident photon flux) of order 1% were measured at low intensities (0.1 mW cm-2). The spectral response of the photocurrent demonstrates that photon absorption near the electron-collecting electrode optimizes the photocurrent, indicating that device performance is limited by low electron mobilities in the bulk PPV. The photocurrent exhibits a weak temperature dependence, with an activation energy that is a function of the electric field in the polymer. We have used these measurements to estimate an exciton binding energy in PPV of approximately 0.4 eV.
342 citations
TL;DR: In this paper, a high performance OFET with pentacene and copper phthalocyanine (CuPC) was fabricated from organic phototransistors (OPTs) based on the geometry of organic field effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined.
Abstract: Organic phototransistors (OPTs) were fabricated from pentacene and copper phthalocyanine (CuPC) based on the geometry of organic field-effect transistors (OFETs); and the effect of the wavelength of the incident light source on their performance was examined High performance OFETs with pentacene and CuPC were fabricated and the characteristics of the OPTs were examined under UV and visible-light irradiations with top illumination The CuPC and pentacene OPTs show a high responsivities of 05–2 and 10–50A∕W and maximum IPh∕IDark of 3000 and 13×105, respectively, under 365nm UV light However, under visible light, at a wavelength of 650nm, the pentacene OPTs had 100 times less responsivity, 015–045A∕W, and a IPh∕IDark of 1000, even though an absorption coefficient three times larger was observed at this wavelength than at 365nm A strong correlation was found between the performance of the OPTs and the incident photon to current conversion efficiency spectra of an organic semiconductor The strong depen
194 citations