Charge-transfer range for photoexcitations in conjugated polymer/fullerene bilayers and blends

Vacar, D.; Maniloff, Eric S.; McBranch, D.; Heeger, Alan J.

doi:10.1103/physrevb.56.4573

Cited by 83 publications

(48 citation statements)

References 22 publications

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“…5 Furthermore, the time-independent form of ␥ A might be too simplistic because it is only valid for collisonal bimolecular annihilation processes. The inclusion of a time dependence [47][48][49] of ␥ A would, however, be beyond the scope of this work.…”

Section: ͑13͒mentioning

confidence: 99%

Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films

et al. 2004

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The electrodeless flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study the photogeneration of charge carriers in spin-coated films of regioregular poly(3-hexylthiophene) ͑P3HT͒, over the photon energy range from 1.9 to 5.2 eV for incident light intensities from 10 13 to 10 16 photons/ cm 2 per ͑3 ns͒ pulse. The initial, single-photon quantum yield of photoionization, , has been estimated from the low-intensity limit to the photoconductivity based on a charge carrier mobility of 0.014 cm 2 /Vs (determined in separate pulse-radiolysis TRMC experiments on bulk P3HT). The value of is constant at ͑1.7± 0.4͒% within the range 1.9-3.0 eV, which encompasses the first electronic absorption band of P3HT. Above 3.0 eV, increases, up to a value of ͑7±2͒% at 5.2 eV. The activation energy of the photoconductivity was found to be approximately 50 meV at all photon energies. The high-intensity, sublinear dependence of the photoconductivity can be described by the occurrence of either exciton-exciton annihilation or diffusional charge recombination with rate coefficients of 2.3ϫ 10 −8 cm 3 / s and 1.1ϫ 10 −8 cm 3 /s.

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Section: ͑13͒mentioning

confidence: 99%

Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films

et al. 2004

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“…[2][3][4][5] Upon photoexcitation of an electron-hole pair, the transfer of electrons from the polymer onto the fullerene leads to an efficient separation of charges that prevents luminescent recombination and is required in photovoltaic devices. Since the charge transfer can only occur if the photoexcitation on the polymer is within less than 10 nm of a C 60 molecule, [6][7][8] close proximity of polymer and fullerene is essential for efficient charge separation. One approach for achieving such close proximity of the electron donor and acceptor materials is by creating a bulk heterojunction.…”

Section: Introductionmentioning

confidence: 99%

Thickness dependence,in situmeasurements, and morphology of thermally controlled interdiffusion in polymer-C60photovoltaic devices

2004

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A series of detailed studies is presented in which heat-induced interdiffusion is used to create a gradient bulk-heterojunction of 2-methoxy-5-(2Ј-ethylhexyloxy͒-1,4-phenylenevinylene ͑MEH-PPV͒ copolymer and C 60 . Starting from a bilayer of spin-cast MEH-PPV and sublimed C 60 , films are heated in the vicinity of the glass transition temperature of the polymer to induce an interdiffusion of polymer and fullerene. Variation of the polymer layer thickness shows that the photocurrents increase with decreasing layer thickness within the examined thickness regime as transport of the separated charges out of the film is improved. The interdiffusion was observed in situ by monitoring the photocurrents during the heating process and exhibited a rapid rise during the first five minutes. Cross-sectional transmission electron microscopy studies show that C 60 forms clusters of up to 30 nm in diameter in the polymer bulk of the interdiffused devices. This clustering of the fullerene molecules puts a significant constraint on the interdiffusion process that can be alleviated by use of donor-acceptor combinations with better miscibility.

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“…2 However, photoexcited electron-hole pairs at distances larger than ϳ10 nm from the fullerene acceptor recombine before charge separation occurs, yielding photoluminescence ͑PL͒. 3,4 Significant improvements of the photovoltaic efficiency have been achieved by providing improved donor/acceptor proximity throughout the device using interpenetrating polymer networks 5,6 and polymer/ fullerene blends, [7][8][9] resulting in ''bulk heterojunctions.'' Nanoscale compositional control of the electron donor and acceptor species is clearly important to optimizing the performance of polymeric photovoltaics.…”

mentioning

confidence: 99%

Creation of a gradient polymer-fullerene interface in photovoltaic devices by thermally controlled interdiffusion

Drees

Premaratne

Graupner

et al. 2002

Applied Physics Letters

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Efficient polymer-fullerene photovoltaic devices require close proximity of the two materials to ensure photoexcited electron transfer from the semiconducting polymer to the fullerene acceptor. We describe studies in which a bilayer system consisting of spin-cast 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene copolymer (MEH-PPV) and sublimed C60 is heated above the MEH-PPV glass transition temperature in an inert environment, inducing an interdiffusion of the polymer and the fullerene layers. With this process, a controlled, bulk, gradient heterojunction is created bringing the fullerene molecules within the exciton diffusion radius of the MEH-PPV throughout the film to achieve highly efficient charge separation. The interdiffused devices show a dramatic decrease in photoluminescence and concomitant increase in short circuit currents, demonstrating the improved interface.

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Charge-transfer range for photoexcitations in conjugated polymer/fullerene bilayers and blends

Cited by 83 publications

References 22 publications

Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films

Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films

Thickness dependence,in situmeasurements, and morphology of thermally controlled interdiffusion in polymer-C60photovoltaic devices

Creation of a gradient polymer-fullerene interface in photovoltaic devices by thermally controlled interdiffusion

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