Vertical confinement and interface effects on the microstructure and charge transport of P3HT thin films

Jimison, Leslie H.; Himmelberger, Scott; Duong, Duc T.; Rivnay, Jonathan; Toney, Michael F.; Salleo, Alberto

doi:10.1002/polb.23265

Cited by 92 publications

(158 citation statements)

References 53 publications

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“…13,17,66,[69][70][71][72] As mentioned above, the structural and optical analyses are bulk measurements, whereas transport measurements in the context of OTFTs is far more sensitive to the polymer order and conformation at the interface. 11 Since surface functionalization has an enhancing effect limited to within approximately 10 nm of the modified interface, 11,40 we speculate that the measured improvements in local order averaged over the entire film depth may be even more pronounced at the interface, perhaps explaining the dramatic enhancement of carrier mobility by nearly two orders of magnitude.…”

Section: Local Order In P3ht Filmsmentioning

confidence: 99%

“…11 Importantly it has been suggested that surface functionalization has an enhancing effect on interfacial order, with the effect limited to within approximately 10 nm of the modified interface, 11,40 which means that the increased molecular order of polymer film at the interface with the OTS-treated substrate may arise from the increased interfacial order in very thin (less than ca. 10 nm) P3HT layer.…”

Section: Otft Device Performancementioning

confidence: 99%

“…11,13 This can be challenging to investigate, as optical and X-ray scattering techniques previously developed to investigate film formation probe mainly the bulk and surface of the drying film, rather than its buried interface. [48][49][50][51][52][53][54][55] We have recently shown that thin film deposition at the solid-liquid interface, solvent vapour annealing and ligand exchange in colloidal quantum dot solids can be monitored using a quartz crystal microbalance with dissipation (QCM-D) capability.…”

Section: P3ht Thin Film Formationmentioning

confidence: 99%

“…[5][6][7][8][9][10] A number of recent studies have demonstrated that molecular ordering along the polymer backbone and between chains is far more important to carrier transport in high molecular weight (Mw) polymer films than domain boundaries. [11][12][13][14][15][16] However, high Mw semi-flexible polymers are thought to be difficult to push into a highly molecularly ordered state due to entanglements and interactions which can inhibit molecular diffusion and challenge conformational transitions. 11,13,17 Polymer crystallization improves the molecular stacking order and planarization of the backbone in the solid state, hence there have been a number of reports linking crystalline order to carrier transport.…”

Section: Introductionmentioning

confidence: 99%

“…[11][12][13][14][15][16] However, high Mw semi-flexible polymers are thought to be difficult to push into a highly molecularly ordered state due to entanglements and interactions which can inhibit molecular diffusion and challenge conformational transitions. 11,13,17 Polymer crystallization improves the molecular stacking order and planarization of the backbone in the solid state, hence there have been a number of reports linking crystalline order to carrier transport. 7,18,19 Along this line, several strategies have been pursued to control molecular self-assembly and thin film microstructure, including by decreasing chain entanglements in the solution state, 12,13,17 tuning solution-processing conditions, [20][21][22][23][24] surface functionalization with a self-assembled monolayer (SAM) [25][26][27] and applying post-deposition thermal/solvent vapour annealing.…”

Section: Introductionmentioning

confidence: 99%

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Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

Khan

et al. 2016

ACS Appl. Mater. Interfaces

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ABSTRACT:We demonstrate that local and long range orders of poly(3-hexylthiophene) (P3HT) semicrystalline films can be synergistically improved by combining chemical functionalization of the substrate with solution-state disentanglement and pre-aggregation of P3HT in a theta solvent, leading to a very significant enhancement of the field effect carrier mobility. The pre-aggregation and surface functionalization effects combine to enhance the carrier mobility nearly 100-fold as compared with standard film preparation by spin-coating, and nearly 10-fold increase over the benefits of pre-aggregation alone. In situ quartz crystal microbalance with dissipation (QCM-D) experiments reveal enhanced deposition of pre-aggregates on surfaces modified with an alkyl-terminated self-assembled monolayer (SAM) in comparison to un-aggregated polymer chains.Additional investigations reveal the combined pre-aggregation and surface functionalization significantly enhances local order of the conjugated polymer through planarization and extension of the conjugated backbone of the polymer which clearly translate to significant improvements of 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 carrier transport at the semiconductor-dielectric interface in organic thin film transistors. This study points to opportunities in combining complementary routes, such as well-known pre-aggregation with substrate chemical functionalization, to enhance the polymer self-assembly and improve its interfacial order with benefits for transport properties.

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Section: Local Order In P3ht Filmsmentioning

confidence: 99%

Section: Otft Device Performancementioning

confidence: 99%

Section: P3ht Thin Film Formationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

Khan

et al. 2016

ACS Appl. Mater. Interfaces

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Entanglement of Conjugated Polymer Chains Influences Molecular Self‐Assembly and Carrier Transport

Zhao

Khan

et al. 2013

Adv Funct Materials

134

195

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The infl uence of polymer entanglement on the self-assembly, molecular packing structure, and microstructure of low-M w (lightly entangled) and high-M w (highly entangled) poly (3-hexylthiophene) (P3HT), and the carrier transport in thin-fi lm transistors, are investigated. The polymer chains are gradually disentangled in a marginal solvent via ultrasonication of the polymer solution, and demonstrate improved diffusivity of precursor species (coils, aggregates, and microcrystallites), enhanced nucleation and crystallization of P3HT in solution, and self-assembly of well-ordered and highly textured fi brils at the solid-liquid interface. In low-M w P3HT, reducing chain entanglement enhances interchain and intrachain ordering, but reduces the interconnectivity of ordered domains (tie molecules) due to the presence of short chains, thus deteriorating carrier transport even in the face of improving crystallinity. Reducing chain entanglement in high-M w P3HT solutions increases carrier mobility up to ≈ 20-fold, by enhancing interchain and intrachain ordering while maintaining a suffi ciently large number of tie molecules between ordered domains. These results indicate that charge carrier mobility is strongly governed by the balancing of intrachain and interchain ordering, on the one hand, and interconnectivity of ordered domains, on the other hand. In high-M w P3HT, intrachain and interchain ordering appear to be the key bottlenecks to charge transport, whereas in low-M w P3HT, the limited interconnectivity of the ordered domains acts as the primary bottleneck to charge transport.

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Mechanism of Crystallization and Implications for Charge Transport in Poly(3‐ethylhexylthiophene) Thin Films

Duong

Shang

et al. 2014

Adv Funct Materials

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In this work, crystallization kinetics and aggregate growth of poly(3‐ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X‐ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time‐dependent, field‐effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2–3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter‐aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics.

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Vertical confinement and interface effects on the microstructure and charge transport of P3HT thin films

Cited by 92 publications

References 53 publications

Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

Entanglement of Conjugated Polymer Chains Influences Molecular Self‐Assembly and Carrier Transport

Mechanism of Crystallization and Implications for Charge Transport in Poly(3‐ethylhexylthiophene) Thin Films

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