The Experts below are selected from a list of 17568 Experts worldwide ranked by ideXlab platform
Ananth Dodabalapur - One of the best experts on this subject based on the ideXlab platform.
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Bimolecular recombination coefficient calculation by in situ potentiometry in a bulk Heterojunction organic photovoltaic material
Applied Physics Letters, 2013Co-Authors: Eric Danielson, Zi En Ooi, Christopher J. Lombardo, Ananth DodabalapurAbstract:Polymer fullerene bulk Heterojunction (BHJ) systems are an important class of active materials; however, charge transport and recombination mechanisms in these materials are not yet completely understood. We use lateral bulk Heterojunction Devices to perform in situ potentiometry on the BHJ system P3HT:PCBM. From current vs. voltage measurements performed at different light intensities, we provide evidence that the recombination mechanism in this material is bimolecular. The potential profile of the device channel is also constructed from these measurements, which is then used to determine the mobility of both charge carriers and calculate the bimolecular recombination coefficient.
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characterization of charge transport via in situ potentiometry in bulk Heterojunction organic photovoltaic materials
SPIE Organic Photonics + Electronics, 2012Co-Authors: Eric Danielson, Christopher Lombardo, Ananth DodabalapurAbstract:The most promising active material for organic photovoltaic (OPV) cells is the polymer/fullerene bulk Heterojunction (BHJ) system, but charge transport and recombination mechanisms in these materials have yet to be completely understood. We report the use of lateral bulk Heterojunction Devices to perform novel material diagnostics on the BHJ system. Using electron beam lithography, we fabricate Devices with up to 24 voltage probes embedded in the channel in order to perform in situ potentiometry. From current vs. voltage measurements performed at a variety of light intensities, we are able to describe the charge transport properties in three distinct regions of a polymer/fullerene BHJ device and determine the dominant recombination mechanism of the OPV material. We note that these are the first such measurements performed on OPV materials. Such measurements will be very useful for materials diagnostics.
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analysis of photocurrents in lateral geometry organic bulk Heterojunction Devices
Applied Physics Letters, 2012Co-Authors: Zi En Ooi, Christopher Lombardo, K L Chan, Ananth DodabalapurAbstract:Lateral-geometry organic bulk Heterojunction (BHJ) Devices resemble field-effect transistors without a gate and are useful for probing electrical characteristics of BHJ blends. The lateral structure allows physical access to the BHJ during device operation and lends itself well to device modelling. Photocurrent-voltage data from P3HT:PCBM-based lateral Devices were found to possess features of space-charge limited (SCL) extraction. Numerical simulations indeed suggest a physical picture of SCL operation, effectively dividing the device into a photogenerative zone and a photoconducting zone. Based on these simulations, an analytical model was created to describe SCL photocurrents that account for channel lengths and bimolecular recombination.
Niyazi Serdar Sariciftci - One of the best experts on this subject based on the ideXlab platform.
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efficiency of bulk Heterojunction organic solar cells
Progress in Polymer Science, 2013Co-Authors: Markus Scharber, Niyazi Serdar SariciftciAbstract:During the last years the performance of bulk Heterojunction solar cells has been improved significantly. For a large-scale application of this technology further improvements are required. This article reviews the basic working principles and the state of the art device design of bulk Heterojunction solar cells. The importance of high power conversion efficiencies for the commercial exploitation is outlined and different efficiency models for bulk Heterojunction solar cells are discussed. Assuming state of the art materials and device architectures several models predict power conversion efficiencies in the range of 10–15%. A more general approach assuming device operation close to the Shockley–Queisser-limit leads to even higher efficiencies. Bulk Heterojunction Devices exhibiting only radiative recombination of charge carriers could be as efficient as ideal inorganic photovoltaic Devices.
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Negative capacitance and its photo-inhibition in organic bulk Heterojunction Devices
Organic Electronics, 2009Co-Authors: Christoph Lungenschmied, Eitan Ehrenfreund, Niyazi Serdar SariciftciAbstract:We report the dynamic admittance, both in the dark and under illumination, of Heterojunctions made of poly(3-hexyl thiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (P3HT:PCBM) blends, which are used in efficient organic solar cells. In the dark there appears a huge low frequency negative capacitance which we associate with slow electron hole bimolecular recombination at the Heterojunction interfaces. Surprisingly, under photoexcitation the negative capacitance gradually disappears with increasing light intensity. We attribute this positive photoinduced capacitance to the combined effect of (1) long lived photogenerated charges at the P3HT:PCBM interfaces that increase electron-hole bimolecular recombination rate, which in turn renders the capacitance less negative and (2) trapped photogenerated charges that increase the capacitance upon re-emission.
Christoph J Brabec - One of the best experts on this subject based on the ideXlab platform.
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physics of organic bulk Heterojunction Devices for photovoltaic applications
Journal of Applied Physics, 2006Co-Authors: Christoph Waldauf, M Scharber, Pavel Schilinsky, Jens Hauch, Christoph J BrabecAbstract:We present investigations of organic photovoltaic Devices consisting of bulk Heterojunction layers made from several material combinations. All of the investigated systems reveal close similarities to the behavior of classical pn-junction Devices. The consequences of the pn-junction-like behavior on the device parameters and performance are presented. Furthermore, device characteristics and parameters of the pristine materials are correlated, resulting in a model that permits an identification of high potential materials, a performance prediction, and a device optimization. The resulting model is able to predict an open circuit voltage and a fill factor and their evolution with the light intensity or thickness of the active layer. It simplifies the identification of the internal morphology and therefore the choice of appropriate solvents. Necessary parameters concerning the choice of electrode materials are also provided.
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recombination and loss analysis in polythiophene based bulk Heterojunction photodetectors
Applied Physics Letters, 2002Co-Authors: Pavel Schilinsky, Christoph Waldauf, Christoph J BrabecAbstract:The monochromatic external quantum efficiency of a bulk Heterojunction photodetector based on a blend of poly-3(hexylthiophene) with a methanofullerene is reported to be as high as 76% at the peak maximum at 25 °C. Analysis of the temperature dependence, the illumination intensity dependence together with absorption measurements in reflection geometry, allow calculation of the internal quantum efficiency of the device close to 100% at the peak maximum. Recombination of photoinduced carriers is negligible or even absent in these photodetectors when operated in the photovoltaic mode. Optical losses in these bulk Heterojunction Devices are analyzed.
Wai-yeung Wong - One of the best experts on this subject based on the ideXlab platform.
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organic donor materials based on bis arylene ethynylene s for bulk Heterojunction organic solar cells with high v oc values
Chemistry-an Asian Journal, 2015Co-Authors: Wai-yeung Wong, Qian Liu, Zhiyuan Xie, Hongmei Zhan, Fengrong Dai, Li ZhaoAbstract:A series of purely organic small molecules 1-4 based on bis(arylene ethynylene)s with various electron-rich aromatic bridges, such as benzene, cyclopentadithiophene (CDT), and diphenyl(p-tolyl)amine, were synthesized by a Sonogashira coupling reaction. Their optical, electronic, and electrochemical properties were fully characterized. The photovoltaic properties of these molecules as donor materials and [6,6]-phenyl-C71 -butyric acid methyl ester as an acceptor material in solution-processed bulk Heterojunction Devices were studied. Among them, CDT-bridged molecule 2 exhibited the best photovoltaic performance and achieved a power conversion efficiency of 3.28 %. In addition, the photovoltaic efficiencies of these molecules are higher than their corresponding platinum-containing counterparts, probably owing to their stronger light absorption and improved open-circuit voltage.
Zi En Ooi - One of the best experts on this subject based on the ideXlab platform.
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Bimolecular recombination coefficient calculation by in situ potentiometry in a bulk Heterojunction organic photovoltaic material
Applied Physics Letters, 2013Co-Authors: Eric Danielson, Zi En Ooi, Christopher J. Lombardo, Ananth DodabalapurAbstract:Polymer fullerene bulk Heterojunction (BHJ) systems are an important class of active materials; however, charge transport and recombination mechanisms in these materials are not yet completely understood. We use lateral bulk Heterojunction Devices to perform in situ potentiometry on the BHJ system P3HT:PCBM. From current vs. voltage measurements performed at different light intensities, we provide evidence that the recombination mechanism in this material is bimolecular. The potential profile of the device channel is also constructed from these measurements, which is then used to determine the mobility of both charge carriers and calculate the bimolecular recombination coefficient.
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analysis of photocurrents in lateral geometry organic bulk Heterojunction Devices
Applied Physics Letters, 2012Co-Authors: Zi En Ooi, Christopher Lombardo, K L Chan, Ananth DodabalapurAbstract:Lateral-geometry organic bulk Heterojunction (BHJ) Devices resemble field-effect transistors without a gate and are useful for probing electrical characteristics of BHJ blends. The lateral structure allows physical access to the BHJ during device operation and lends itself well to device modelling. Photocurrent-voltage data from P3HT:PCBM-based lateral Devices were found to possess features of space-charge limited (SCL) extraction. Numerical simulations indeed suggest a physical picture of SCL operation, effectively dividing the device into a photogenerative zone and a photoconducting zone. Based on these simulations, an analytical model was created to describe SCL photocurrents that account for channel lengths and bimolecular recombination.