The impact of molecular weight on microstructure and charge transport in semicrystalline polymer semiconductors–poly(3-hexylthiophene), a model study

Koch, Felix P.; Rivnay, Jonathan; Foster, Sam; Müller, Christian; Downing, Jonathan M.; Buchaca‐Domingo, Ester; Westacott, Paul; Yu, Liyang; Yuan, Mingjian; Baklar, Mohammed A.; Fei, Zhuping; Luscombe, Christine K.; McLachlan, Martyn A.; Heeney, Martin; Rumbles, Garry; Silva, Carlos; Salleo, Alberto; Nelson, Jenny; Smith, Paul; Stingelin, Natalie

doi:10.1016/j.progpolymsci.2013.07.009

Cited by 281 publications

(398 citation statements)

References 48 publications

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“…For example, charge transport in P3HT has been found to display clear trends with molecular weight and whether the film displays one-phase (polycrystalline) or two-phase (entangled) morphologies. In field-effect transistors, Kline et al observed a systematic increase in field-effect mobilities up to a weight-average molecular weight of 40 kg/mol; [12][13][14] in agreement with reports by Zhang et al 15 and Koch et al 16 On the other hand, bulk mobilities display more complex trends with molecular weight, and depend sensitively on film processing routes. Ballantyne et al found, for instance, an order-of-magnitude decrease in bulk charge mobilities for P3HT of molecular weight M w >18 kg/mol.…”

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confidence: 78%

“…For materials of higher molecular weight, the time-of-flight mobility was found to be again reduced, leveling at a value of ~10 -4 cm 2 /Vs. 16 However, when films were cast at 115 o C, the mobility increased by over an order of magnitude for materials of M w <10 kg/mol, and decreased by over two orders of magnitude for P3HT of M w ≈ 60 kg/mol. 16 In this contribution, we focus on the nature of excitons in regioregular P3HT with molecular weights ranging from 3-450 kg/mol, where the microstructure changes from chain-extended crystals to a semicrystalline morphology where amorphous and crystalline domains are interconnected.…”

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confidence: 98%

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Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

et al. 2013

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The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer's chemical nature and molecular weight. Specifically, lowmolecular-weight materials form crystalline domains of cofacially π-stacked molecules, while the usually entangled nature of higher molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the π-stack, depending on the structural development with molecular weight.Such two-dimensional excitations can be considered as Frenkel excitons in the limit of weak intersite coupling. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT) -one of the most extensively studied polymer semiconductors -of weight-average molecular weight (M w ) of 3-450 kg/mol. In thin-film structures of high-molecular-weight materials (M w > 50 kg/mol), a balance of intramolecular and intermolecular excitonic coupling results in high exciton coherence lengths along chains (~4 thiophene units), with interchain coherence limited to ~2.5 chains. In contrast, for structures of low-M w P3HT (<40 kg/mol), the interchain exciton coherence is dominant (~20% higher than in architectures formed by high-molecular-weight materials). In addition, the spatial coherence within the chain is significantly reduced (by nearly 30%). These observations give valuable structural information; they suggest that the macromolecules in aggregated regions of high-molecular-weight P3HT adopt a more planar conformation compared to low-molecular-weight materials. This results in the observed increase in intrachain exciton coherence. In contrast, shorter chains seem to lead to torsionally more disordered architectures. A rigorous, fundamental description of primary photoexcitations in π-conjugated polymers is hence developed: two-dimensional excitons are defined by the chain-length dependent molecular arrangement and interconnectivity of the conjugated macromolecules, leading to interplay between intramolecular and intermolecular spatial coherence.

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confidence: 98%

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

et al. 2013

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“…A quantitative understanding of exciton migration in conjugated polymers is important for applications in organic photovoltaics, lightemitting diodes and lasers [1][2][3][4][5] . In polymer films excitons migrate along conjugated chains as well as between chains [6][7][8][9][10] .…”

Section: Introductionmentioning

confidence: 99%

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

et al. 2015

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Electronic energy transfer (EET) in organic materials is a key mechanism that controls the efficiency of many processes, including light harvesting antenna in natural and artificial photosynthesis, organic solar cells, and biological systems. In this paper we have examined EET in solid-state thin-films of polyfluorene, a prototypical conjugated polymer with ultrafast photoluminescence experiments and theoretical modelling. We observe EET occurring on a 680 ± 300 fs timescale by looking at the depolarisation of photoluminescence. An * To whom correspondence should be addressed independent, predictive microscopic theoretical model is built by defining 125 000 chromophores containing both spatial and energetic disorder appropriate for a spin-coated thin film. The model predicts time-dependent exciton dynamics, without any fitting parameters, using the incoherent Förster-type hopping model. Electronic coupling between the chromophores is calculated by an improved version of the usual line-dipole model for resonant energy transfer. Without the need for higher level interactions, we yet find that the model is in general agreement with the experimentally observed 680 ± 300 fs depolarisation caused by EET. This leads us to conclude that femtosecond EET in polyfluorene can be well described by conventional resonant energy transfer, as long as the relevant microscopic parameters are well captured. The implications of this finding are that dipole-dipole resonant energy transfer can in some circumstances be fully adequate to describe ultrafast EET without needing to invoke strong or intermediate coupling mechanisms.1

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“…P3HT is known to form self-organized structures upon annealing [33]. Regular stacking of the individual P3HT chains is beneficial for charge transport as it increases the charge mobility in the direction of stacking through intermolecular π-π interactions and it also benefits absorption at longer wavelengths as inter-chain interactions are enhanced [34].…”

Section: P Steiger Et Al Thin Solid Films 645 (2018) 417-423mentioning

confidence: 99%

Hydrothermally grown ZnO electrodes for improved organic photovoltaic devices

et al. 2018

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A B S T R A C THere we report a simple, solution based processing route for the formation of large surface area electrodes resulting in improved organic photovoltaic devices when compared with conventional planar electrodes. The nanostructured electrode arrays are formed using hydrothermally grown ZnO nanorods, subsequently infiltrated with blends of poly(3-hexylthiophene-2,5-diyl) (P3HT) and indene-C 60 bisadduct (IC 60 BA) as photoactive materials. This well studied organic photoactive blend allows the composition/processing/performance relationships to be elucidated. Using simple solution based processing the resultant nanostructured devices exhibited a maximum power conversion efficiency (PCE) of 2.5% compared with the best planar analogues having a PCE of around 1%. We provide detailed structural, optical and electrical characterization of the nanorod arrays, active layers and completed devices giving an insight into the influence of composition and processing on performance. Devices were fabricated in the desirable inverse geometry, allowing oxidation resistant high work-function top electrodes to be used and importantly to support the hydrothermal growth of nanorods on the bottom electrode -all processing was carried out under ambient conditions and without the insertion of a hole transport layer below the anode. The nanorods were successfully filled with the active layer materials by carrying out a brief melt processing of a spin-cast top layer followed by a subsequent thermal anneal which was identified as an essential step for the fabrication of operational devices. The growth method used for nanorod fabrication and the active layer processing are both inherently scalable, thus we present a complete and facile route for the formation of nanostructured electron acceptor layers that are suitable for high performance organic active layers.

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The impact of molecular weight on microstructure and charge transport in semicrystalline polymer semiconductors–poly(3-hexylthiophene), a model study

Cited by 281 publications

References 48 publications

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

Hydrothermally grown ZnO electrodes for improved organic photovoltaic devices

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