Efficient Organic Heterojunction Photovoltaic Cells Based on Triplet Materials

Shao, Yan; Yang, Yang

doi:10.1002/adma.200501297

Cited by 266 publications

(228 citation statements)

References 29 publications

(31 reference statements)

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“…52,67,68 For example, triplet diffusion lengths of 18.0 AE 0.6 nm and 5.7 AE 0.5 nm have been measured for amorphous films of platinum(II) octaethylporphyrin (PtOEP) (phosphorescence QY = 0.45) and platinum(II) tetraphenyltetrabenzoporphyrin (PtTPBP) (phosphorescence QY = 0.51), respectively. 52 In this method, the strongly phosphorescent material is cast as a film and then a thin quenching layer (usually composed of fullerene or TiO 2 ) is brought into contact with it ( Fig.…”

Section: Visualizing and Quantifying Triplet Exciton Diffusion Inmentioning

confidence: 99%

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Triplet transport in thin films: fundamentals and applications

Tang

2017

Chem. Commun.

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Triplet excitons are key players in multi-excitonic processes like singlet fission and triplet-triplet annihilation based photon upconversion, which may be useful in next-generation photovoltaic devices, photocatalysis and bioimaging. Here, we present an overview of experimental and theoretical work on triplet energy transfer, with a focus on triplet transport in thin films. We start with the theory describing Dexter-mediated triplet energy transfer and the fundamental parameters controlling this process. Then we summarize current experimental methods used to measure the triplet exciton diffusion length. Finally, the use of hierarchically ordered structures to improve the triplet diffusion length is presented, before concluding with an outlook on the remaining challenges.

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Section: Visualizing and Quantifying Triplet Exciton Diffusion Inmentioning

confidence: 99%

“…52,65,68,[72][73][74][75][76][77] Here, it is important to distinguish between the contributions of triplet and singlet excitons to photocurrent. The effect of triplet-triplet annihilation also leads to inaccuracies as discussed above.…”

Section: (3) Photocurrent In Solar Cellsmentioning

confidence: 99%

Triplet transport in thin films: fundamentals and applications

Tang

2017

Chem. Commun.

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“…In phosphorescent organic light-emitting devices, triplet exciton diffusion plays a major role: it has been recently reported that one can take advantage of it to efficiently monitor energy transport from the exciton creation zone up to the emissive dopants to allow fine color tuning [3,4]. Exciton diffusion also plays a key role in bilayer photovoltaic organic devices as it governs the exciton dissociation efficiency [5,6]. In these cases, the interesting characteristic of triplet excitons is their long diffusion length compared to singlet excitons.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of triplet excitons in an operational organic light-emitting diode

et al. 2009

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Measurements of the diffusion length L for triplet excitons in small molecular-weight organic semiconductors are commonly carried out using a technique in which a phosphorescent-doped probe layer is set in the vicinity of a supposed exciton generation zone. However, analyses commonly used to retrieve L ignore microcavity effects that may induce a strong modulation of the emitted light as the position of the exciton probe is shifted. The present paper investigates in detail how this technique may be improved to obtain more accurate results for L. The example of 4,4'-bis(carbazol-9-yl)1,1'-biphenyl (CBP) is taken, for which a triplet diffusion length of L=16 ± 4 nm (at 3 mA/cm 2 ) is inferred from experiments. The influence of triplet-triplet annihilation, responsible for an apparent decrease of L at high current densities, is theoretically investigated, as well as the 'invasiveness' of the thin probe layer on the exciton distribution. The interplay of microcavity effects and direct recombinations is demonstrated experimentally with the archetypal trilayer structure [N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)]-4,4'-diaminobiphenyl (NPB)/CBP/ 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (named bathocuproine, BCP). It is shown that in this device holes do cross the NPB/CBP junction, without the assistance of electrons and despite the high energetic barrier imposed by the shift between the HOMO levels. The use of the variablethickness doped layer technique in this case is then discussed. Finally, some guidelines are given for improving the measure of the diffusion length of triplet excitons in operational OLEDs, applicable to virtually any small molecular-weight material.

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“…[28][29][30] For example, iridium compounds are used to induce singlet-triplet decay in conjugated polymers. 31 It is possible then that the close proximity of the heavy Eu atoms to the nanotube induces singlet-triplet mixing among the nanotube excitonic states. This hypothesis implies that the EuS is merely a source for spin orbit coupling, which could also be provided by any number of heavy metal compounds.…”

Section: Discussionmentioning

confidence: 99%

Photoexcitation of the triplet exciton in single wall carbon nanotubes

et al. 2009

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The carbon nanotube photoexcitation spectrum is dominated by excitonic transitions, rather than interband transitions between continuum states. There are eight distinct excitonic transitions (four singlet and four triplet), each with two-fold degeneracy. Because the triplet excitons are spin polarized with electron and hole spins both pointing in the same direction, they are optically inactive, and optical spectroscopy has revealed no evidence for their existence. Here, we show that by the interaction with a spin filter ferromagnetic semiconductor, photoexcitation of the carbon nanotube triplet exciton is possible, and its contribution to the photocurrent can be detected. The perturbation provided by the spin filter allows for inter-system mixing between the singlet and triplet excitonic states, and relaxes the spin selection rules. This supplies the first evidence for the existence of the triplet exciton, and provides an avenue for the optical excitation of spin polarized carriers in carbon nanotubes.

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Efficient Organic Heterojunction Photovoltaic Cells Based on Triplet Materials

Cited by 266 publications

References 29 publications

Triplet transport in thin films: fundamentals and applications

Triplet transport in thin films: fundamentals and applications

Diffusion of triplet excitons in an operational organic light-emitting diode

Photoexcitation of the triplet exciton in single wall carbon nanotubes

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