Scanning Near-Field and Confocal Raman Microscopic Investigation of P3HT−PCBM Systems for Solar Cell Applications

Klimov, Evgueni; Li, W; Yang, Xiaoniu; Hoffmann, Gerhard; Loos, Joachim

doi:10.1021/ma052590x

Cited by 138 publications

(128 citation statements)

References 32 publications

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“…Superior path balance for case 1 can be one of the reasons for the reported improved performance via a postannealing protocol. [1][2][3][4][5][6][7]10 iii. Intra-and Intermolecular Transport along Hole Pathways.…”

Section: Resultsmentioning

confidence: 99%

Electrode Materials, Thermal Annealing Sequences, and Lateral/Vertical Phase Separation of Polymer Solar Cells from Multiscale Molecular Simulations

Lee

Wodo

Ganapathysubramanian

et al. 2014

ACS Appl. Mater. Interfaces

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The nanomorphologies of the bulk heterojunction (BHJ) layer of polymer solar cells are extremely sensitive to the electrode materials and thermal annealing conditions. In this work, the correlations of electrode materials, thermal annealing sequences, and resultant BHJ nanomorphological details of P3HT:PCBM BHJ polymer solar cell are studied by a series of large-scale, coarse-grained (CG) molecular simulations of system comprised of PEDOT:PSS/ P3HT:PCBM/Al layers. Simulations are performed for various configurations of electrode materials as well as processing temperature. The complex CG molecular data are characterized using a novel extension of our graph-based framework to quantify morphology and establish a link between morphology and processing conditions. Our analysis indicates that vertical phase segregation of P3HT:PCBM blend strongly depends on the electrode material and thermal annealing schedule. A thin P3HT-rich film is formed on the top, regardless of bottom electrode material, when the BHJ layer is exposed to the free surface during thermal annealing. In addition, preferential segregation of P3HT chains and PCBM molecules toward PEDOT:PSS and Al electrodes, respectively, is observed. Detailed morphology analysis indicated that, surprisingly, vertical phase segregation does not affect the connectivity of donor/acceptor domains with respective electrodes. However, the formation of P3HT/PCBM depletion zones next to the P3HT/PCBM-rich zones can be a potential bottleneck for electron/hole transport due to increase in transport pathway length. Analysis in terms of fraction of intraand interchain charge transports revealed that processing schedule affects the average vertical orientation of polymer chains, which may be crucial for enhanced charge transport, nongeminate recombination, and charge collection. The present study establishes a more detailed link between processing and morphology by combining multiscale molecular simulation framework with an extensive morphology feature analysis, providing a quantitative means for process optimization.

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Section: Resultsmentioning

confidence: 99%

Electrode Materials, Thermal Annealing Sequences, and Lateral/Vertical Phase Separation of Polymer Solar Cells from Multiscale Molecular Simulations

Lee

Wodo

Ganapathysubramanian

et al. 2014

ACS Appl. Mater. Interfaces

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“…In blend materials however, when annealed, the segregated PCBM small molecules diffuse into the P3HT matrix allowing the latter to re-organize itself into stacks and long chains as a result of the increase in mean free volume. Raman microscopy results have previously shown that upon annealing the relative position of P3HT remains largely the same while that of PCBM changes, a clear indication that PCBM aggregates and diffuses into P3HT matrix during the annealing process (Klimov et al, 2006;Marchaut and Foot, 1997;Hugger et al, 2003;Zhao et al, 2009). This study indicates that crystallization of P3HT in the blends upon annealing improves the absorption of the films and causes a red shift to occur in the spectra of the blends.…”

Section: The Characteristic High Resolution Transmission Electron Micmentioning

confidence: 98%

Characterization and optimization of poly (3-hexylthiophene-2, 5- diyl) (P3HT) and [6, 6] phenyl-C61-butyric acid methyl ester (PCBM) blends for optical absorption

Kalonga¹,

Chinyama²,

Munyati³

et al. 2013

J. Chem. Eng. Mater. Sci.

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Thin films were developed, characterized, and optimized for optical absorbance from blends of organic polymer poly (3-hexylthiophene-2, 5-diyl) (P3HT) and the fullerene derivative [6, 6] phenyl-C 61 -butyric acid methyl ester (PCBM). The materials of both pristine and blends were analyzed using X-ray diffraction spectroscopy and high resolution transmission electron microscopy for structural properties, and fourier transform infra-red and UV-VIS spectroscopy for optical properties. The study evaluated the effects of altering the blend ratio and annealing temperature on absorption. The ratios were made by varying the weight of PCBM whilst keeping that of P3HT constant. Eleven different ratios were made with each exhibiting its own optimal annealing temperature and absorption. The optimum ratio was determined and found to be at 1:1 with an annealing temperature of 100ºC for 30 min duration.

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“…1,[9][10][11] It is less clear, however, how annealing affects the fullerene component of a BHJ polymer solar cell: the way in which the fullerene molecules are distributed in the polymer matrix and the details of the BHJ morphology have been the subject of much debate. 1,2,9,10,[12][13][14][15] In this work, we directly address the question of what happens to the fullerene component of a polymer BHJ solar cell upon thermal annealing. By fabricating "fullerene-only" BHJ halfdevices (that use electronically insulating polystyrene (PS) rather than a semiconducting polymer like P3HT), we show that thermal annealing causes a decrease in the ability of the fullerene network to conduct electrons as a result of increased phase segregation of the blended polymer and fullerene components.…”

Section: Introductionmentioning

confidence: 99%

Room to Improve Conjugated Polymer-Based Solar Cells: Understanding How Thermal Annealing Affects the Fullerene Component of a Bulk Heterojunction Photovoltaic Device

et al. 2008

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We examine how thermal annealing affects the fullerene network in conjugated polymer bulk heterojunction (BHJ) solar cells. We begin by creating electron-only devices with a BHJ geometry by blending the fullerene derivative [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) with polystyrene (PS). These electron-only PS:PCBM diodes function even with a poly(ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS) layer, indicating that PEDOT:PSS films do not serve as electron blocking layers. Atomic force microscopy shows that the degree of phase segregation in the PS:PCBM blend films is similar to that in the active layer of blends of PCBM with poly(3-hexylthiophene-2,5-diyl) (P3HT), so that the PS:PCBM blends provide a good model for the fullerene part of the BHJ network in P3HT:PCBM solar cells. We find that thermal annealing dramatically decreases the electron current that flows in the PS:PCBM diodes, suggesting that annealing leads to increased phase segregation that lowers the electron mobility on fullerenes in the BHJ geometry. We also find that annealing increases the photoluminesence of P3HT:PCBM blend films, indicating that thermal treatment produces increased phase segregation that leads to decreased exciton harvesting. The fact that annealing decreases both exciton harvesting and electron mobility implies that there is significant room to further improve polymer/fullerene photovoltaics by controlling the amount of phase segregation.

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Scanning Near-Field and Confocal Raman Microscopic Investigation of P3HT−PCBM Systems for Solar Cell Applications

Cited by 138 publications

References 32 publications

Electrode Materials, Thermal Annealing Sequences, and Lateral/Vertical Phase Separation of Polymer Solar Cells from Multiscale Molecular Simulations

Electrode Materials, Thermal Annealing Sequences, and Lateral/Vertical Phase Separation of Polymer Solar Cells from Multiscale Molecular Simulations

Characterization and optimization of poly (3-hexylthiophene-2, 5- diyl) (P3HT) and [6, 6] phenyl-C61-butyric acid methyl ester (PCBM) blends for optical absorption

Room to Improve Conjugated Polymer-Based Solar Cells: Understanding How Thermal Annealing Affects the Fullerene Component of a Bulk Heterojunction Photovoltaic Device

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