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  • Roberto Pacios
Roberto Pacios

Roberto Pacios
Ikerlan · Microfluidic, Microsensors, Encapsulation and Microsystems Integration and Organic Electronics Department

PhD Physics

About

39
Publications
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2,695
Citations

Publications

Publications (39)
Article
There is an increasing demand for built-in flow sensors in order to effectively control microfluidic processes due to the high number of available microfluidic applications. The possible solutions should be inexpensive and easy to connect to both, the microscale features and the macro setup. In this paper, we present a novel approach to integrate a...
Article
Solution-processed organic photovoltaics are advantageous due to their low-cost large area manufacturing techniques, such as slot-die coating, gravure printing and roll-to-roll coating. The final microstructure of a polymer:fullerene bulk-heterojunction (BHJ) film is a competition between solution thermodynamics (e.g. solubility, miscibility…) and...
Article
Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applicati...
Conference Paper
Full-text available
We present a simple, low-cost, pioneering technique for the metallization of polymeric substrates that allows manufacturing of 3D-PCBs for fully encapsulated Smart Systems. This 3D packaging approach provides a compact solution to integrate MEMs with fluidics in a durable substrate, opening the door to adapting Smart Systems to harsh environments o...
Article
Full-text available
In spite of the impressive development achieved by organic photovoltaics throughout the last decades, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing,...
Article
Full-text available
Accurate characterization and reporting of organic photovoltaic (OPV) device performance remains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing.The presented article...
Article
Full-text available
In this work we study the different electrical loss pathways occurring during the operation of bulk heterojunction solar cells by using a variety of electrical and optical characterization techniques beyond the current density–voltage curve (J–V): Impedance Spectroscopy (IS), Charge Extraction (CE) and Transient Photovoltage (TPV). Two sets of devi...
Article
Abstract This work studies the charge carrier collection efficiency in organic bulk-heterojunction solar cells based on polymer:fullerene blends. An equivalent circuit with a specific recombination term is proposed to describe the behavior of this type of devices. It is experimentally shown that this recombination term determines the slope of the c...
Article
In this work, diketopyrrolopyrrole-based polymer bulk heterojunction solar cells with inverted and regular architecture have been investigated. The influence of the polymer:fullerene ratio on the photoactive film nanomorphology has been studied in detail. Transmission Electron Microscopy and Atomic Force Microscopy reveal that the resulting film mo...
Article
This work describes a patterning technique for the photoactive layer of organic photovoltaic modules. We demonstrate the fabrication of efficient poly[3-(hexyl)thiophene-2,5-diyl]:[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) based organic photovoltaic modules through a specific surface treatment, based on the deposition of a fluorinated s...
Article
Full-text available
Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, tra...
Article
We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a transparent conducting electrode. Current limitations to achieve high conversion efficiencies are overcome with the combination of Ag NW and specifically designed ZnO nanoparticles (NP). The new transparent electrode presents improved optoelectronic prop...
Chapter
Full-text available
Quantum dots (QDs) are inorganic semiconductor particles that exhibit size and shape dependent optical and electronic properties. Due to the typical dimension in the range of 1-100 nm, the surface-to-volume ratios of the materials become large and their electronic states become discrete. Moreover, due to the fact that the size of the semiconductor...
Article
Organic field effect transistors, photodiodes and solar cells based on polymer–fullerene blend active lay-ers are printed electronic applications under intense studies. We show that the viscosity of the inkjet for-mulation, substrate temperature, drop spacing and the height of the droplet in relation to the surface are critical parameters to achiev...
Article
Full-text available
1-Dimensional nanostructured ZnO electrodes have been demonstrated to be potentially interesting for their application in solar cells. Herein, we present a novel procedure to control the ZnO nanowire optoelectronic properties by means of surface modification. The nanowire surface is functionalized with ZnO nanoparticles in order to provide an impro...
Article
Full-text available
In this study, full coincidence between impedance spectroscopy and transient photovoltage techniques in measuring recombination kinetics of photogenerated charge carriers in inverted polymer:fullerene organic solar cells with ZnO hole-blocking layer is reported. Carrier lifetime exhibits values at illumination intensities near 1 sun within the micr...
Article
Here the role of metal oxide (ZnO) electron-selective layers in the operating mechanisms of bulk-heterojunction polymer−fullerene solar cells is addressed. Inverted as well as regular structures containing ZnO layers at the cathode contact have been analyzed using capacitance methods in the dark and impedance spectroscopy under illumination. We sys...
Article
We have measured the charge transfer processes on near IR small molecule solution processes solar cells under working conditions. The results show that there are two different behavior, for the device under working conditions, controlled by the intrinsic properties of the organic bulk-heterojunction phase to store charges at the different organic m...
Article
Full-text available
We report organic photovoltaic devices in which the standard ITO transparent electric contact has been substituted by lower cost ultrathin metallic electrodes. Solution and vacuum processable n and p-type semiconductors provide the electrode with the rectifying behavior of the diode. We are in this way able to invert the built-in electric field at...
Article
Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective electrodes for electron collection. The interfacial charge transfer reactions, under working conditions, that limit the energy conversion efficiency of these devices have been measured and compared to the standard OPSC geometry which collects the electrons...
Article
Full-text available
Energy distributions [density-of-states (DOS)] of defects in the effective band gap of organic bulk heterojunctions are determined by means of capacitance methods. The technique consists of calculating the junction capacitance derivative with respect to the angular frequency of the small voltage perturbation applied to thin film poly(3-hexylthiophe...
Article
We present a detailed study and experimental recipes to tune the outcoming light of single layer polymeric diodes fabricated with commercially available polyfluorene. The standard blue emission peaking at 440 nm can be tuned to obtain even white emission by controlling the deliberate oxidation of the material. Furthermore, with the addition of inor...
Article
Since the demonstration of efficient hybrid photovoltaic devices using CdSe/P3HT, a number of different QD/polymer molecular solar cells have been investigated. However, considerably less attention has been paid to the photo-induced processes occurring in these devices, in particular the strong dependence that device efficiencies show upon QD conce...
Article
Full-text available
In order to get a deeper understanding of the conduction mechanisms limiting the electrical characteristics of ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells, dark current-voltage measurements at different temperatures were analyzed using a compact electrical equivalent circuit previously used in p/n junctions. Between 0.2 V and 0.6 V, the current-voltage...
Article
Charge carrier diffusion and recombination in an absorber blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) with indium tin oxide (ITO) and aluminium contacts have been analyzed in the dark by means of impedance spectroscopy. Reverse bias capacitance exhibits Mott–Schottky-like behavior indicating the form...
Article
In this paper, a new method for obtaining poly(3,4-ethylenedioxythiophene) (PEDOT/PSS)/gold nanocomposites is described. In a first step, PEDOT/PSS gold nanoparticle aqueous dispersions were obtained by simultaneous chemical synthesis of PEDOT and gold nanoparticles in the presence of PSS that acts as a stabilizer. In a second step, these PEDOT/PSS...
Article
Full-text available
Poly(3,4-ethylenedioxithiophene)/poly(styrene sulphonate) (PEDOT/PSS) aqueous dispersions were mixed with aqueous gold nanoparticle and aqueous silver nanoparticle colloids. PEDOT/gold nanoparticles (Au NP) and PEDOT/silver nanoparticles (Ag NP) films were obtained by solvent casting the corresponding aqueous solutions. The nanocomposite films show...
Article
Full-text available
We present a study of dark air-exposure degradation of organic solar cells based on photoactive blends of the conjugated polymer, poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Photovoltaic devices were fabricated on indium tin oxide (ITO) glass with or without a...
Article
A study of the photo-oxidation of films of poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) blended with [6,6]-phenyl C-61-butyric acid methyl ester (PCBM), and solar cells based thereon, is presented. Solar-cell performance is degraded primarily through loss in short-circuit current density, J(SC). The effect of the sam...
Article
Full-text available
We present a study of charge transfer in polyfluorene: [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend films. After photoexciting the conjugated polymer, electrons are very quickly transferred onto the PCBM leaving positive charges in the polymer. The presence of new photogenerated species in both polymer and PCBM can be demonstrated by pho...
Article
Full-text available
We present a study of charge recombination in polyfluorene:[6,6]-Phenyl C61-butyric acid methyl ester (PCBM) blend photovoltaic cells. The recombination kinetics of photogenerated charge carriers are investigated at room temperature by frequency and time domain photoinduced absorption. Monomolecular and bimolecular recombination processes are discu...
Article
We present a study of charge transport in polyfluorene:[6,6]-phenyl C<sub>61</sub> -butyric acid methyl ester (PCBM) blend films. The electron and hole mobilities, measured via time-of-flight photocurrent experiments, show a strong dependence on the PCBM concentration. As a result, ambipolar transport can be obtained in blends of two otherwise unip...
Article
We present a study of photocurrent generation and charge transport in polyfluorene/PCBM blend films. Diode rectification ratios of 106 and photocurrent (PC) enhancements of four orders of magnitude over the dark response make the polyfluorene/PCBM blend system a sensitive photodiode material and one of the most promising polymer blend systems for u...
Article
The photosensitivity of semiconducting polymers can be enhanced by blending donor (D) and acceptor (A) polymers to optimise photoinduced charge separation. The photoluminescence of two such polymers, an acceptor poly(9,9-dioctylfluorene-co-benzothidiadiozole) (BT) and a donor poly(9,9-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenylbenzi...

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