Mapping electric field distributions in biased organic bulk heterojunctions under illumination by nonlinear optical microscopy

Morris, J. D.; Atallah, Timothy; Lombardo, Christopher; Park, Heungman; Dodabalapur, Ananth; Xy, Zhu

doi:10.1063/1.4788707

Cited by 20 publications

(14 citation statements)

References 27 publications

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“…Similar EFISH measurements on PSBTBT:PCBM films did not shown rapid SCR formation, suggesting that these materials may be more resilient to environmental degradation. 22 EFISH can also be used to measure actual charge carrier concentrations within different device regions, utilizing the differential form of Gauss's law…”

Section: Efish Microscopymentioning

confidence: 99%

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Analysis of bulk heterojunction material parameters using lateral device structures

et al. 2014

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Abstract. We review the key optoelectronic properties of lateral organic bulk heterojunction (BHJ) device structures with asymmetric contacts. These structures are used to develop a detailed model of charge transport and recombination properties within materials used for organic photovoltaics. They permit a variety of direct measurement techniques, such as nonlinear optical microscopy and in situ potentiometry, as well as photoconductive gain and carrier drift length studies from photocurrent measurements. We present a theoretical framework that describes the charge transport physics within these devices. The experimental results presented are in agreement with this framework and can be used to measure carrier concentrations, recombination coefficients, and carrier mobilities within BHJ materials. Lateral device structures offer a useful complement to measurements on vertical photovoltaic structures and provide a more complete and detailed picture of organic BHJ materials. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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Section: Efish Microscopymentioning

confidence: 99%

“…Details on EFISH microscopy fundamentals can be found in previously published work. 22,23 A laser pulse energy was selected so as to generate an average photocurrent density equivalent to that generated under AM1.5 illumination.…”

Section: Efish Microscopymentioning

confidence: 99%

Analysis of bulk heterojunction material parameters using lateral device structures

et al. 2014

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“…This observed imbalance is consistent with EFISH measurements of lateral P3HT:PCBM devices over similar time scales. 27 A rapid increase in the voltage across the electron dominated SCR was noted and attributed to photo-oxidation introducing negatively charge electron traps, resulting from moisture within the device. 27,28 This procedure was repeated with the same P3HT:PCBM solution, but with 5% by volume of the solvent additive DIO (1,8-diiodooctane).…”

Section: A Degradation Under High Background Pressurementioning

confidence: 98%

Use of lateral structures to monitor and evaluate degradation of key photovoltaic parameters in an organic bulk heterojunction material

Danielson

Ooi

Dodabalapur

2014

Journal of Applied Physics

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Charge transport and recombination mechanisms within organic bulk heterojunction (BHJ) systems have been studied using lateral devices to perform in situ potentiometry. We have developed a simplified measurement technique using two types of lateral structures to elicit key charge transport parameters and study the time and process dependence of the carrier mobilities and their ratio. Small geometry lateral devices are used to evaluate the mobility of the slower carrier within the P3HT:PCBM material system. Larger structures with 5 in situ voltage probes are used to construct a simple potential profile of the device channel and accurately determine the carrier mobility ratio. These two measurements enable the calculation of carrier densities and the recombination coefficient. We monitor the change in these parameters as the P3HT:PCBM film degrades in the presence of oxygen and also examine the effect of the solvent additive 1,8-diiodooctane on this degradation mechanism. By exposing ethanol vapor to the BHJ film, we induce traps in the material and monitor the shift in dominant nongeminate recombination mechanism to a more unimolecular type. We are also able to measure the resulting decrease in carrier mobilities due to the presence of dipole-induced traps. Lateral devices are useful material diagnostic structures for studying degradation in BHJ materials.

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“…Studies of the local charge transport within the OSC with scanning Kelvin probe microscopy (SKPM) 8 can help to gain a deeper understanding of the structure-function relationship and bridge the gap from nanoscopic to meso-and macroscopic understanding. Unlike the above mentioned methods, [5][6][7] SKPM allows for mapping of the electrical field distribution within the OSC under operating conditions. Its results can give detailed information on how charge is transported in the cell.…”

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“…1, 2 Highest power conversion efficiencies of up to 8.6 percent 3 are achieved by employing a so-called bulk heterojunction (BHJ) structure. 4 Despite many efforts undertaken in the research on BHJ OSCs, for example by transmission electron microscopy, 5 optical microscopy 6 or with scanning probe microscopy methods, 7 the principles that govern the device operation are not completely understood yet. The nanoscopic phase segregation of the materials in the BHJ does not allow a clear distinction between bulk and interface phenomena.…”

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Sample preparation for scanning Kelvin probe microscopy studies on cross sections of organic solar cells

et al. 2013

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We prepared cross sections of P3HT:PCBM bulk heterojunction (BHJ) organic solar cells (OSCs) for the characterization of their potential distribution with scanning Kelvin probe microscopy. We compared results of samples obtained by microtome cutting of OSCs on plastic substrates, cleaving of OSCs on glass substrates, and milling with a focused ion beam. Their potential distributions were in good agreement with each other. Under short circuit conditions, potential gradients were detected in vicinity of the electrode/organics interfaces, with negligible electric fields within the bulk. We contacted the OSCs in a defined manner and studied their potential distribution under operating conditions

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Mapping electric field distributions in biased organic bulk heterojunctions under illumination by nonlinear optical microscopy

Cited by 20 publications

References 27 publications

Analysis of bulk heterojunction material parameters using lateral device structures

Analysis of bulk heterojunction material parameters using lateral device structures

Use of lateral structures to monitor and evaluate degradation of key photovoltaic parameters in an organic bulk heterojunction material

Sample preparation for scanning Kelvin probe microscopy studies on cross sections of organic solar cells

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