A photophysical study of PCBM thin films

Cook, Steffan; Ohkita, Hideo; Kim, Youngkyoo; Benson-Smith, Jessica J.; Bradley, Donal D. C.; Durrant, James R.

doi:10.1016/j.cplett.2007.08.005

Cited by 160 publications

(169 citation statements)

References 26 publications

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“…26,27 Although we have discussed HT as splitting of a PCBM exciton in the presence of pBTTT, we cannot exclude the alternative scenario of hole injection into the polymer following spontaneous charge dissociation within the PCBM clusters and charge migration (this would lead to similar evolution of the TA spectra). The process has been demonstrated, 51,52 but is probably slower than what we observe here and therefore has a minor inuence on our results. 53 In summary, we have shown that charge separation in the completely intercalated 1 : 1 blend predominantly occurs on the ultrafast ($100 fs) time scale, no matter whether the pBTTT or PCBM is initially excited.…”

Section: Resultscontrasting

confidence: 41%

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The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

et al. 2014

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Light-induced charge formation is essential for the generation of photocurrent in organic solar cells. In order to gain a better understanding of this complex process, we have investigated the femtosecond dynamics of charge separation upon selective excitation of either the fullerene or the polymer in different bulk heterojunction blends with well-characterized microstructure. Blends of the pBTTT and PBDTTPD polymers with PCBM gave us access to three different scenarios: either a single intermixed phase, an intermixed phase with additional pure PCBM clusters, or a three-phase microstructure of pure polymer aggregates, pure fullerene clusters and intermixed regions. We found that ultrafast charge separation (by electron or hole transfer) occurs predominantly in intermixed regions, while charges are generated more slowly from excitons in pure domains that require diffusion to a charge generation site.The pure domains are helpful to prevent geminate charge recombination, but they must be sufficiently small not to become exciton traps. By varying the polymer packing, backbone planarity and chain length, we have shown that exciton diffusion out of small polymer aggregates in the highly efficient PBDTTPD:PCBM blend occurs within the same chain and is helped by delocalization.

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Section: Resultscontrasting

confidence: 41%

“…The analysis remains of course simplistic, because delocalization between coupled PCBM molecules is not accounted for. 52 In Fig. 4B (polymer excitation at 530 nm), the spectral changes are clearly different from the ones caused by slow HT.…”

Section: Part Ii: Charge Generation In Pbdttpd:pcbmmentioning

confidence: 99%

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

et al. 2014

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“…49 The small sharp 1.75 eV absorption is due to the formation of a "Frenkel exciton" (electron hole pair within the same fullerene). 29,49 The direct excitation of this state is forbidden by the selection rules of the icosahedral fullerene, 55,56 but emission from this state can be observed in photoluminescence spectra of PCBM. 49 The SPV spectrum of the PCBM film contains a negative feature at 1.1−1.4 eV and a positive one at 1.4−2.3 eV.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…29,49 The direct excitation of this state is forbidden by the selection rules of the icosahedral fullerene, 55,56 but emission from this state can be observed in photoluminescence spectra of PCBM. 49 The SPV spectrum of the PCBM film contains a negative feature at 1.1−1.4 eV and a positive one at 1.4−2.3 eV. The fine structure of feature 1 (F1) is caused by the specific emission lines of the Xe arc lamp, as detailed in our earlier paper.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface Photovoltage Spectroscopy

et al. 2014

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Surface photovoltage (SPV) spectra are reported for separate films of (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) and for regioregular and regiorandom poly(3-hexylthiophene) (P3HT):PCBM bulk heterojunctions, as a function of wavelength, film thickness, thermal annealing, and substrate. In PCBM films, two photovoltage features are observed at 1.1–1.4 eV (F1) and 1.4–2.3 eV (F2), which are assigned to excitation of charge transfer states at the interface (F1) and in the bulk (F2) of the film. In BHJ films, five different photovoltage features are observed at 0.75–0.9 eV (F1), 0.9–1.3 eV (F2), 1.3–1.8 eV (F3), 1.8–2.0 eV (F4), and 2.0–2.4 eV (F5). This data can be analyzed on the basis of optical absorbance and fluorescence spectra of the films, and using SPV spectra for PCBM and P3HT only films, and for a BHJ film containing P3HT nanofibers for comparison. SPV features are assigned to states at the polymer–substrate interface (F1 and F2), the P3HT:PCBM charge transfer state (F3), the self-ionized (CT) state of P3HT (F4), and the band gap transition of P3HT (F5). This interpretation is also consistent with molecular orbital energy diagrams and electron microscopy-derived topological maps of the films. Photovoltage sign and substrate dependence can be understood with the depleted semiconductor model. Features F1–4 are caused by polarization of electrostatically bound charge pairs by the built-in electric field at the substrate–BHJ interface, whereas F5 is due to transport of free charge carriers through the film and through the substrate film interface. This work will promote the understanding of photochemical charge generation and transport in organic photovoltaic films.

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“…1 A relatively small number of non-fullerene acceptors have been reported but very few exhibit acceptable quantum efficiencies within organic photovoltaic cells 26 . This is problematic for narrowband red or NIR OPDs since the fullerenes all possess significant blue-green absorption-considerably broadening the overall device response and/or rendering the detector non-blind in the visible 14,27 . The best narrowband red and NIR OPDs to date are based on engineering the absorption spectrum of the materials, rather than a broadband junction plus filter or prism designs 8,28 .…”

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confidence: 99%

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

et al. 2015

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Spectrally selective light detection is vital for full-colour and near-infrared (NIR) imaging and machine vision. This is not possible with traditional broadband-absorbing inorganic semiconductors without input filtering, and is yet to be achieved for narrowband absorbing organic semiconductors. We demonstrate the first sub-100 nm full-width-at-half-maximum visible-blind red and NIR photodetectors with state-of-the-art performance across critical response metrics. These devices are based on organic photodiodes with optically thick junctions. Paradoxically, we use broadband-absorbing organic semiconductors and utilize the electro-optical properties of the junction to create the narrowest NIR-band photoresponses yet demonstrated. In this context, these photodiodes outperform the encumbent technology (input filtered inorganic semiconductor diodes) and emerging technologies such as narrow absorber organic semiconductors or quantum nanocrystals. The design concept allows for response tuning and is generic for other spectral windows. Furthermore, it is materialagnostic and applicable to other disordered and polycrystalline semiconductors.

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A photophysical study of PCBM thin films

Cited by 160 publications

References 26 publications

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface Photovoltage Spectroscopy

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

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