Contactless determination of the efficiency of interfacial charge separation in a TiO2/phenylene vinylene polymer junction

Savenije, Tom J.; Vermeulen, M. J. W.; Haas, Matthijs P. de; Warman, John M.

doi:10.1016/s0927-0248(99)00092-6

Cited by 40 publications

(41 citation statements)

References 21 publications

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“…These results are in full agreement with those reported earlier. 29 The photoconductance transient for the PPV: PCBM 0.50 / TiO 2 bilayer obtained on excitation at 510 nm exhibits a much slower increase than the instrument limited rise of the transient for the MDMO-PPV/ TiO 2 bilayer. Hence, the photoconductance in the PPV: PCBM 0.50 / TiO 2 bilayer is not due to fast production of electrons in TiO 2 by dissociation of excitons at the interface between MDMO-PPV and TiO 2 .…”

Section: Optical Properties and Transient Photoconductancementioning

confidence: 89%

“…Hence, the photoconductance in the PPV: PCBM 0.50 / TiO 2 bilayer is not due to fast production of electrons in TiO 2 by dissociation of excitons at the interface between MDMO-PPV and TiO 2 . Previous work has demonstrated that visible excitation of PPV: PCBM x / quartz 18 or bare TiO 2 layers 29,30 alone results in much smaller and faster ͑response-time limited͒ photoconductance signals. Therefore, the relatively slow rise of the photoconductance for the PPV: PCBM 0.50 / TiO 2 bilayer is attributed to diffusion of electrons from the blend film into the TiO 2 layer ͑see Fig.…”

Section: Optical Properties and Transient Photoconductancementioning

confidence: 99%

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Electron diffusion in polymer:fullerene bulk heterojunctions

et al. 2007

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A method to study the bulk electron diffusion dynamics in poly͑2-methoxy-5-͑3Ј, 7Ј-dimethyloctyloxy͒-1,4-phenylene-vinylene͒: 1-͑3-methoxycarbonyl͒-propyl-1-phenyl-͑6,6͒ C 61 ͑PCBM͒ blend films with varying PCBM content is presented. The blends are spin coated on top of dense smooth TiO 2 and excited with a visible laser pulse. The photogenerated electrons on PCBM diffuse through the blend film until they reach the interface with TiO 2 , which serves to collect the electrons. The resulting change in conductance of TiO 2 is measured using the time-resolved microwave conductivity technique. Theoretical analysis of the timedependent photoconductance gives the electron diffusion constant ͑D e ͒ and the lower limit of the time for electrons to decay by trapping or recombination ͑ e ͒. D e increases from 7.0ϫ 10 −13 m 2 / s at a weight fraction PCBM ͑W PCBM ͒ = 0.11 to 3.5ϫ 10 −10 m 2 /s at W PCBM = 0.50, while, interestingly, at W PCBM = 0.75, a smaller value of 1.2ϫ 10 −10 m 2 / s is found. The electron diffusion length increases with PCBM content. The presence of PCBM clusters in blends with a high PCBM content extends the time for electrons to decay, so that the lower limit of the electron diffusion length exceeds the film thickness of 100 nm, which is required for sufficient light absorption in a photovoltaic device.

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Section: Optical Properties and Transient Photoconductancementioning

confidence: 89%

Section: Optical Properties and Transient Photoconductancementioning

confidence: 99%

Electron diffusion in polymer:fullerene bulk heterojunctions

et al. 2007

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“…9 GHz͒ using microwave circuitry and detection equipment, which has been described elsewhere. [11][12][13][14] The two parameters are related by…”

Section: Methodsmentioning

confidence: 99%

“…The aforementioned problems can be circumvented using the flash-photolysis time-resolved microwave conductivity ͑FP-TRMC͒ technique, [11][12][13][14] which operates at low electricfields ͑ഛ100 V cm −1 ͒. Charge carriers are detected by the absorption of microwaves and no electrodes or dc fields are required.…”

Section: Introductionmentioning

confidence: 99%

Signature of exciton annihilation in the photoconductance of regioregular poly(3-hexylthiophene)

2005

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The transient photoconductance in drop-cast films of regioregular poly͑3-hexylthiophene͒ has been studied over the photon energy range from 1.7 to 2.8 eV for incident light intensities from 10 13 to 10 16 photons/ cm 2 per 4 ns pulse. Charge carriers were detected using an electrodeless, time-resolved microwave conductivity technique. The photon-energy dependence of the photoconductance for a 15 m thick, optically dense film was found to be very different from that of a submicrometer thick film, which could not be explained by the differences in light absorption alone. A model based on exciton-exciton annihilation, however, with a rate coefficient of ͑0.9± 0.8͒ ϫ 10 −8 cm 3 / s, can reproduce the spectra as a function of film thickness and incident intensity. From kinetic fits of the conductance transients, bimolecular charge recombination can be excluded as the main origin of the nonlinear dependence of the photoconductance on the light intensity. The quantum yield of photoionization, , was found to be constant at ͑2.5± 0.4͒% within the investigated photon energy range.

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“…While such an approach may seem good in theory, the highest global efficiency reported to date is only 0.5% 7 . There have been only a few reports of research into the photovoltaic mechanisms of this device configuration 5,[10][11][12][13] and further investigation is needed for the cells to reach their full potential.…”

Section: Introductionmentioning

confidence: 99%

Nanocomposite titanium dioxide/polymer photovoltaic cells: effects of TiO 2 microstructure, time, and illumination power

et al. 2004

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Nanocomposite titanium dioxide/polymer photovoltaic cells have been fabricated using poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEHPPV). Two different types of titanium dioxide were used, one synthesized using a sol-gel method, the other was a commercial paste. The crystal structure, porosity and absorption spectra of the titanium dioxide layers were measured, and the titanium dioxide synthesized using the sol-gel method had a much lower level of anatase. The photovoltaic properties of the ITO/TiO 2 /MEHPPV/Au cells, which were similar for both types of TiO 2 , were measured as a function of illumination power and compared with equivalent circuit models. A simple equivalent circuit model incorporating a diode, two resistances and a light induced current was inconsistent with the illumination -dependent data and was improved by adding an illumination dependent shunt resistance. A very long lived, photo-induced increase in dark current was observed, which could not be explained by a polymer degradation mechanism or an increase in temperature under illumination, but was more likely to be due to trapped charge.

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Contactless determination of the efficiency of interfacial charge separation in a TiO2/phenylene vinylene polymer junction

Cited by 40 publications

References 21 publications

Electron diffusion in polymer:fullerene bulk heterojunctions

Electron diffusion in polymer:fullerene bulk heterojunctions

Signature of exciton annihilation in the photoconductance of regioregular poly(3-hexylthiophene)

Nanocomposite titanium dioxide/polymer photovoltaic cells: effects of TiO 2 microstructure, time, and illumination power

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