Long-Range Singlet Energy Transfer in Perylene Bis(phenethylimide) Films

Gregg, Brian A.; Sprague, and Julian; Peterson, M. W.

doi:10.1021/jp9703263

Cited by 141 publications

(186 citation statements)

References 47 publications

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“…By comparing the PL intensity of a polymer film on a planar quenching substrate and a non-quenching substrate for a range of polymer film thickness, the exciton diffusion length (L d ) can be determined. [64][65][66] Glass was used as the non-quenching substrate, while a thin layer of TiO 2 coated on glass with or without IM was the quenching substrate. Thin TiO 2 (~5 -8 nm) was used to ensure a negligible effect from optical interference.…”

Section: Models For Increased Photocurrent Yieldmentioning

confidence: 99%

“…When deposited on bare TiO 2 or -NH 2 modified TiO 2 , P3HT exhibits some quenching at large thickness, but the quenching never approaches 100% as its thickness is reduced. 64 This lack of complete quenching is unexpected because in very thin film of polymers (d < L d ), all the excitons should be able to diffuse to the quenching interface. For thin films where the absorption is assumed to be linear with thickness, the quenching profile follows:…”

Section: Models For Increased Photocurrent Yieldmentioning

confidence: 99%

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Effects of molecular interface modification in hybrid organic-inorganic photovoltaic cells

Goh¹,

Scully²,

McGehee³

2007

Journal of Applied Physics

443

457

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We have systematically investigated the effects of surface modification of titania (TiO 2 ) in hybrid TiO 2 /regioregular poly(3-hexylthiophene) (P3HT) photovoltaic cells.By employing a series of para-substituted benzoic acids with varying dipoles and a series of multiply-substituted benzene carboxylic acids, the energy offset at the TiO 2 /polymer interface and thus the open circuit voltage of devices can be tuned systematically by 0.25 V. Transient photovoltage measurements showed that the recombination kinetics were dominated by charge carrier concentration in these devices and were closely associated with the dark current. The saturated photocurrent of TiO 2 /P3HT devices exhibits more than a two-fold enhancement when molecular modifiers with large electron affinity were employed. The ability of modifiers to accept charge from polymers, as revealed in photoluminescence quenching measurement with blends of polymers, was shown to be correlated to the enhancement in device photocurrent.A planar geometry photoluminescence quenching measurement showed that TiO 2 substrates modified by these same molecules that accept charge quenched more excitons in regioregular P3HT than bare TiO 2 surfaces. An exciton diffusion length in P3HT as large as 6.5 -8.5 nm it was found that all of the excitons that were quenched were accountable as extracted photocurrent. EQE was effectively increased from 5% to 10 -14% with certain surface modifiers; consequently exciton harvesting was more than doubled. The use of Ruthenium (II) sensitizing dyes with good exciton harvesting property coupled with suppression of the recombination kinetics improved the efficiency of optimized bilayer TiO 2 /P3HT devices from 0.34 % to 0.6 % under AM 1.5 solar illuminations. The implication of this work is directly relevant to the design of nanostructured bulk heterojunction inorganic-organic cells, in which efficient exciton harvesting and control of the recombination kinetics are key to achieving high efficiency. _____________________________ a) Electronic

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Section: Models For Increased Photocurrent Yieldmentioning

confidence: 99%

Section: Models For Increased Photocurrent Yieldmentioning

confidence: 99%

Effects of molecular interface modification in hybrid organic-inorganic photovoltaic cells

Goh¹,

Scully²,

McGehee³

2007

Journal of Applied Physics

443

457

View full text Add to dashboard Cite

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“…The development of accurate measurements of the exciton diffusion length is therefore important for organic photovoltaics and the optimisation of materials, processing and device structure. To date there has been a wide range of reported values for different materials obtained by techniques such as surface quenching, [5][6][7][8] volume quenching, [9,10] microwave conductivity, [11] exciton-exciton annihilation [12,13] and photocurrent modelling of solar cells. [14] Of these the surface quenching technique is probably the most used, where the organic material is deposited onto a suitable quencher, resulting in a loss of luminescence.…”

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confidence: 99%

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

2008

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Polymer solar cells are a promising technology for future power generation. In particular the polymer poly (3-hexylthiophene) (P3HT) has attracted widespread interest with power conversion efficiencies close to 5%. [1][2][3][4] Such devices employ the bulk heterojunction device structure, where the polymer is blended with a strong charge acceptor such as a fullerene. The processing of the blend affects its morphology and the formation of domains of P3HT-rich and fullerene-rich regions. It is at the interface between these two domains that excitons are dissociated into their constituent charges, a critical step in the operation of a solar cell. Excitons are only able to diffuse a short distance during their lifetime and therefore the size of the domains should ideally be on the order of the diffusion length, maximising the number of excitons reaching the interface and undergoing dissociation. The development of accurate measurements of the exciton diffusion length is therefore important for organic photovoltaics and the optimisation of materials, processing and device structure. To date there has been a wide range of reported values for different materials obtained by techniques such as surface quenching, [5][6][7][8] volume quenching, [9,10] microwave conductivity, [11] exciton-exciton annihilation [12,13] and photocurrent modelling of solar cells. [14] Of these the surface quenching technique is probably the most used, where the organic material is deposited onto a suitable quencher, resulting in a loss of luminescence. This loss can be quantified by comparing the emission from the quenched film with that of an identical film on a non-quenching substrate and will depend on the diffusion coefficient and the thickness of the organic film. This experiment can be performed via steady-state or time-resolved with most employing the former. However, a problem in steady-state measurements is that interference effects in the layer structures used can strongly modify the amount of light absorbed. [7] Time-resolved techniques do not require absolute measurements of the luminescence as it is only the decay of the emission from the material that is actually needed, though the initial excitation profile is influenced by optical interference. Exciton diffusion in polymers occurs on a time range from 1 ps to $1 ns, [15] thus any measurements should aim to cover this range. In this communication we will describe how time-resolved measurements of fluorescence, coupled with an appropriate quencher, enable robust measurements of the diffusion coefficient. We have applied this technique to the polymer P3HT, which despite being the most used polymer in organic photovoltaic research, has had little published on its exciton diffusion. Kroeze et al.[11] reported a value for the diffusion length of 2.6-5.3 nm from time-resolved microwave conductivity measurements, depending on whether or not excitons were reflected at the polymer/air interface. Using oxygen-induced fluorescence quenching in P3HT, Lü er et al. [9] obtained a minimum value...

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“…[9] Recent studies have shown BPE-PTCDI to be an excellent n-channel organic semiconductor, possessing both a high n-type mobility (≈ 0.1 cm 2 V -1 s -1 ) and good stability in air over several weeks. [11] A remarkably long exciton diffusion length of 2.3 lm was estimated [12] for solvent-annealed, evaporated thin films of this material, making it an attractive candidate for use in bilayer device structures. Its HOMO level was measured to be -6.1 eV by ultraviolet photoelectron spectroscopy (IPES) [13] indicating that it is a strong acceptor with respect to CuPc (HOMO = -5.0 eV).…”

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confidence: 99%