Enhanced Charge Transfer Doping Efficiency in J-Aggregate Poly(3-hexylthiophene) Nanofibers

Gao, Jian; Stein, Benjamin W.; Thomas, Alan K.; García, José Antonio Tornero; Yang, Jing; Kirk, Martin L.; Grey, John K.

doi:10.1021/acs.jpcc.5b05191

Cited by 68 publications

(96 citation statements)

References 49 publications

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“…Doped spectra exhibit distinct quinoidal distortions (i.e., redistribution of intensities for CC stretches, ~1390-1470 cm -1 ), which are not observed in H-aggregates (not shown). [7] These features are consistent with trends observed from both EPR and absorption measurements, namely, J-aggregates are more efficiently doped than their H-aggregate counterparts. …”

Section: Order Dependent Charge Transfer Doping and Polaron Interactionssupporting

confidence: 86%

“…Doping studies of P3HT aggregates involve combining solution dispersions with varying amounts of a small molecule charge transfer dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 -TCNQ), and characterized using electron paramagnetic resonance (EPR), electronic absorption and Raman spectroscopy. [7] 3. RESULTS AND DISCUSSION…”

Section: Methodsmentioning

confidence: 99%

“…Interestingly, J-aggregates show lower polaron levels at larger dopant loadings (e.g., EPR spin density) that we assign as formation of a spinless bipolaron species from anti-ferromagnetic coupling of polaron spins on neighboring P3HT chains. [7] This observation implies that the ultimate limit of doping efficiency is determined largely by spin-spin interactions of injected carriers and not complex formation or lack of suitable doping sites as commonly found in thin films.…”

Section: Introductionmentioning

confidence: 99%

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Exciton and polaron interactions in self-assembled conjugated polymer aggregates

2015

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We study exciton coupling and interconversion between neutral and charged states of different spin in pi-stacked conjugated polymer aggregates. Rigorous self-assembly approaches are used to prepare aggregate nanofibers that permit reliable control of polymer chain conformational and packing (intra-and interchain) order within these structures. Exciton coupling can be tuned between the H-and J-aggregate limits, which has important implications for determining the fates of excitons and polarons. Single molecule intensity modulation spectroscopy was performed on individual nanofibers and large quenching depths of emissive singlet excitons by triplets are found in J-aggregate type structures. We propose that high intrachain order leads to exciton delocalization that effectively lowers singlet-triplet energy splittings thus increasing triplet yields. Exciton-polaron and polaron-polaron interactions are next investigated in both H-and J-type nanofibers where polarons are injected by charge transfer doping. We find that the enhanced intrachain order of J-aggregates enables efficient intrachain polaron transport and leads to significantly larger doping efficiencies than less ordered H-aggregates. As polaron densities increase, signatures of spin-spin interactions between polarons on adjacent chains become appreciable leading to the formation of a spinless bipolaron. Overall, these studies demonstrate the potential for controlling and directing exciton and polaron interactions via tuning of subtle intra-and interchain ordering characteristics of aggregates, which could benefit various polymeric optoelectronic applications.

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Section: Order Dependent Charge Transfer Doping and Polaron Interactionssupporting

confidence: 86%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exciton and polaron interactions in self-assembled conjugated polymer aggregates

2015

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“…[2][3][4][5][6][7][8] Molecular dopants such as F4TCNQ undergo groundstate charge transfer with their host semiconductor, yielding polarons or bipolarons on the semiconductor. 5,[8][9][10][11][12][13][14][15] The dopant anions remain in the film as counter-ions (radical anions in the case of F4TCNQ). This process is relatively straightforward, however, details of the mechanism remain unclear.…”

Section: Introductionmentioning

confidence: 99%

Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology

et al. 2016

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Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate that sequential doping occurs rapidly (o1 s), and that the film doping level can be precisely controlled by varying the concentration of the doping solution. Furthermore, the choice of sequential doping solvent controls whether dopant anions are included or excluded from polymer crystallites. Atomic force microscopy (AFM) reveals that sequential doping produces significantly more uniform films on the nanoscale than the mixed-solution method. In addition, we show that mixedsolution doping induces the formation of aggregates even at low doping levels, resulting in drastic changes to film morphology. Sequentially coated films show 3-15 times higher conductivities at a given doping level than solution-doped films, with sequentially doped films processed to exclude dopant anions from polymer crystallites showing the highest conductivities. We propose a mechanism for doping induced aggregation in which the shift of the polymer HOMO level upon aggregation couples ionization and solvation energies.To show that the methodology is widely applicable, we demonstrate that several different polymer:dopant systems can be prepared by sequential doping.

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“…Even for ground-state electron transfer, the effi ciency of free charge generation has been associated with local molecular order. [ 18 ] Theoretical interpretations of these observations are varied, and have been thoroughly reviewed. [ 19 ] One very common and quite intuitive argument is that local molecular order delocalizes the manifold of charge transfer states, leading to a strong reduction in the coulomb binding energy because the effective initial separation distance of electrons and holes is increased.…”

Section: Introductionmentioning

confidence: 99%

Local Intermolecular Order Controls Photoinduced Charge Separation at Donor/Acceptor Interfaces in Organic Semiconductors

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Reid

Pace

et al. 2016

Advanced Energy Materials

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How free charge is generated at organic donor–acceptor interfaces is an important question, as the binding energy of the lowest energy (localized) charge transfer states should be too high for the electron and hole to escape each other. Recently, it has been proposed that delocalization of the electronic states participating in charge transfer is crucial, and aggregated or otherwise locally ordered structures of the donor or the acceptor are the precondition for this electronic characteristic. The effect of intermolecular aggregation of both the polymer donor and fullerene acceptor on charge separation is studied. In the first case, the dilute electron acceptor triethylsilylhydroxy‐1,4,8,11,15,18,22,25‐octabutoxyphthalocyaninatosilicon(IV) (SiPc) is used to eliminate the influence of acceptor aggregation, and control polymer order through side‐chain regioregularity, comparing charge generation in 96% regioregular (RR‐) poly(3‐hexylthiophene) (P3HT) with its regiorandom (RRa‐) counterpart. In the second case, ordered phases in the polymer are eliminated by using RRa‐P3HT, and phenyl‐C61‐butyric acid methyl ester (PC61BM) is used as the acceptor, varying its concentration to control aggregation. Time‐resolved microwave conductivity, time‐resolved photoluminescence, and transient absorption spectroscopy measurements show that while ultrafast charge transfer occurs in all samples, long‐lived charge carriers are only produced in films with intermolecular aggregates of either RR‐P3HT or PC61BM, and that polymer aggregates are just as effective in this regard as those of fullerenes.

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Enhanced Charge Transfer Doping Efficiency in J-Aggregate Poly(3-hexylthiophene) Nanofibers

Cited by 68 publications

References 49 publications

Exciton and polaron interactions in self-assembled conjugated polymer aggregates

Exciton and polaron interactions in self-assembled conjugated polymer aggregates

Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology

Local Intermolecular Order Controls Photoinduced Charge Separation at Donor/Acceptor Interfaces in Organic Semiconductors

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