B. Arredondo

High-Bandwidth Organic Photodetector Analyzed by Impedance Spectroscopy

An organic bulk heterojunction photodetector (OPD) is fabricated on the basis of a blend of poly(3-hexyl thiophene):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6) C61. The OPD responsivity is calculated from current density-voltage characteristic (J-V) under green-LED illumination obtaining 1 A/W. Frequency response at different biases is measured, which shows a high-3-dB cutoff frequency of 343 kHz at -3 V . Impedance measurements are carried out at different reverse biases, and the results are fitted with a small signal equivalent circuit. The device cutoff frequency (fc) can be estimated with the parameters extracted from this circuit obtaining good agreement between measured and calculated (fc).

Bis(pyridylpyrazolate)platinum(II): a mechanochromic complex useful as a dopant for colour-tunable polymer OLEDs

The photoluminescence and mechanochromic behaviour of the bis(3-(3,5-bis(dodecyloxy)phenyl)-(5-pyridin-2-yl)pyrazolate)platinum(II) complex PT12, selected from a series of Pt(II) compounds with N,N′-pyridylpyrazolate ligands, has been investigated. The electroluminescence properties of polymer OLEDs based on PT12-doped polyfluorene (PFO) are also described. Addition of PT12 induces the formation of the PFO β-phase, a much more ordered phase with enhanced colour stability at high bias and high photoluminescence quantum efficiency. Additionally, the characteristic blue emission of PFO is red-shifted for PT12 concentrations equal to or higher than 3%. Depending on the dopant concentration and the applied current, the colour coordinates of these polymer OLEDs undergo a broad shift in the CIE colour space. In addition, through the strategic use of keto defect sites, white-emitting devices can be fabricated with a very small addition of PT12.

A project-oriented integral curriculum on Electronics for Telecommunication Engineers

This paper describes the Electronics curriculum in the Telecommunication Engineer degree at Rey Juan Carlos University (URJC) in Spain. Telecommunication Engineering started in the 2003–2004 academic year. In these years, all the electronic courses have been set up with a main practical orientation and with Project Based Learning (PBL) activities, both compulsory and voluntary. Once these courses have been successfully implemented we have reoriented some of the practical activities to be more interlaced. In this sense, projects involving students of different courses have been developed, as well as projects involving students from different years. All these activities fit in the principles promulgated by the Declaration of Bologna, which results in the actual updating of the university degree structure in Spain.

Extraction of circuital parameters of organic solar cells using the exact solution based on Lambert W-function

The electrical behavior of organic solar cell (OSC) has been analyzed using a simple circuital model consisting on an ideal diode together with a series and parallel resistances (RS and RP respectively). Applying Kirchhoffs Laws to the circuit leads to a transcendental equation that can be solved numerically without approximations using the Lambert W function. Theoretical expression has been fitted to experimental current-voltage (I-V) curves under forward bias, obtaining fairly accurate values for the electrical parameters. This model has been validated comparing the extracted parameters for dark and illumination conditions of different devices. Results show good agreement for RS, and ideality factor (η). Electrical parameters obtained in this work are also compared to those ones extracted using an approximated method often employed by other authors 1. We conclude that approximated method leads to reasonable good values for RS, RP and η. However, in the case of Rp the voltage range chosen to fit the data with the exact method must be constrained to the fourth quadrant, where the role of parallel resistance is more critical. To validate the model, a bunch of organic solar cells with structure ITO/ poly(3,4-ethylenedioxythiophene)-poly (4-styrene sulfonate (PEDOT:PSS)/ poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM)/Al has been fabricated in inert atmosphere. Different active layers were deposited varying the P3HT:PCBM ratio (1:0.64, 1:1, 1:1.55) and the active layer thickness (ranging from 100 to 280 nm). Devices are encapsulated inside the glove-box prior its characterization outside the glove-box. Electro optical characterization has been performed with a halogen lamp. Values extracted for RS range from 142 Ω to 273 Ω, values for RP range from 25 kΩ to 331 kΩ. Ideality factor ranges from 5 to 17.

Novel lithographic technology for OLED-based display manufacturing

Common cathode organic electroluminescent diode matrices, based on a new CN-derivative of poly(2,7-fluorene phenylidene) have been developed by photolithography. Optical characterization reveals their interesting properties as white-light emitters. In addition, 7times5 pixel alphanumeric display prototypes have been manufactured using a novel lithographic technique that saves processing steps and costs.

P-172: Determination of Hole Mobilities in New Blue Emitting Organic Diodes by Means of Impedance Spectroscopy

In this work we have fabricated passive diode matrices based on a new blue emitting organic electroluminescent polymer. In order to determine the capacitive response at typical display operating frequencies, impedance vs frequency measurements have been carried out at different bias. In addition, hole mobilities have been extracted by fitting a new theoretical model to the measured admittance, that takes into account the effect of an injection barrier, obtaining values from 10−12 m2/Vs to 10−10 m2/Vs with increasing bias.

An All-Organic Flexible Visible Light Communication System

Visible light communication systems can be used in a wide variety of applications, from driving to home automation. The use of wearables can increase the potential applications in indoor systems to send and receive specific and customized information. We have designed and developed a fully organic and flexible Visible Light Communication system using a flexible OLED, a flexible P3HT:PCBM-based organic photodiode (OPD) and flexible PCBs for the emitter and receiver conditioning circuits. We have fabricated and characterized the I-V curve, modulation response and impedance of the flexible OPD. As emitter we have used a commercial flexible organic luminaire with dimensions 99 × 99 × 0.88 mm, and we have characterized its modulation response. All the devices show frequency responses that allow operation over 40 kHz, thus enabling the transmission of high quality audio. Finally, we integrated the emitter and receiver components and its electronic drivers, to build an all-organic flexible VLC system capable of transmitting an audio file in real-time, as a proof of concept of the indoor capabilities of such a system.

Thickness dependence of organic photodetector bandwidth

Organic bulk heterojunction photodiodes based on a blend of poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-1-phenyl-(6, 6)C61 (P3HT:PCBM) have been fabricated with different active layer thicknesses. Current-voltage characteristics and cut-off frequency were measured under Green-LED illumination. Impedance measurements were performed and a simple equivalent circuit was used to fit the resulting Cole-cole diagram. Parameters obtained from the fit were used to estimate the theoretical photodetector cut-off frequency and compared to the experimental one. The material dielectric constant was estimated using the capacitance obtained from the impedance fit.

Influence of cathode in organic solar cells performance

In this work we have fabricated and characterized organic solar cells (OSC) based on blends of polyhexylthiophene (P3HT) and [6,6]-phenil-C61-butyric acid methyl ester (PCBM) with two different cathodes: Al and LiF/Al. Current- Voltage (I-V) curves under illumination have been measured and fitted with the standard equivalent circuit in order to extract circuital parameters, such as series and parallel resistances (Rs and Rp) ideality factor (n) and inverse saturation current (I0). The introduction of a thin layer (0.5 nm) of LiF between active layer and Al increases the open circuit voltage (Voc) but slightly reduces short current (Isc) and fill factor (FF). The overall result is a slight increase of the efficiency, from 2.53 % to 2.57 %. Circuital parameters have been extracted with two methods (approximated an exact), and results show that structures with LiF layer have lower parasitic effects (lower Rs and higher Rp).

A complete model for electrical behaviour of single carrier organic diodes in the presence of a field-dependent mobility

In this paper we propose a model to simulate electrical conduction of single carrier organic diodes in the presence of a barrier for carrier injection, and considering a field-dependent carrier mobility. An analytical expression for the internal electric field function, that simplifies operation with the resulting non-linear equation system, is provided. The results of the model are compared with those from other existing approaches that assume simplifications. Finally, the current density versus voltage curves predicted by this model for diodes with different active layer thicknesses show a good agreement with the experimental results.