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

Abstract

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.

Morphology Development in Solution-Processed Functional Organic Blend Films: An In Situ Viewpoint

“…For these reasons, the authors of this review have developed optical absorbance measurements performed through the entire depth of the thinning solution and wet film, as this is more likely to capture aggregation and related structural changes occurring during solution processing with the added bonus of not having to resort to optical modeling to obtain the absorption coefficient. In situ absorbance studies carried out on neat P3HT films preaggregated in a theta solvent or well-dissolved in a warmer solution (Figure ) clearly show differences in the aggregation state of the solution and its subsequent drying behavior, with more aggregated films formed when processing from a theta solvent resulting in improved carrier transport in OTFTs, in agreement with previous observations. − Similar experiments performed on P3HT:PCBM in oDCB clearly reveal the two distinct regimes of solution ejection/outflow and structure evolution/aggregation. Having understood the process and its kinetics makes it possible, for instance, to interrupt the spin coating during outflow to impact the film thickness and drying rate by restricting the extent of outflow as compared to uninterrupted spin-coating experiments and slowing down the evaporation.…”

Impact of the Solvation State of Lead Iodide on Its Two‐Step Conversion to MAPbI3: An In Situ Investigation

“…However, further progress in the implementation of two‐step conversion requires a deeper understanding of the conversion process to perovskite, requiring the use of in situ characterization methods which can be sensitive to temporal changes in the phase, composition and microstructure, optical properties as well as mass uptake. Toward this end, techniques such as grazing incidence wide‐angle X‐ray scattering (GIWAXS), UV–vis transmission/reflection, and quartz crystal microbalance with dissipation (QCM‐D), are especially powerful as they can be combined with commonly used solution‐casting techniques to monitor in situ the ink‐to‐solid phase transformation in organic and hybrid semiconductors …”

Improving Charge Carrier Mobility of Polymer Blend Field Effect Transistors with Majority Insulating Polymer Phase

“…For high performance FET applications, it is critically important to control the morphology and microstructure of solution processed P3HT films by improving polymer chain order and alignment and enhancing the π–π stacked structures. For this purpose, both intrinsic molecular parameters involving regioregularity and molecular weight − and extrinsic parameters involving solvent, , deposition method, − polymer–dielectric layer interface, − doping, and post-thermal treatment ,, have been explored to tune the morphology and microstructure to be favorable for efficient charge transport.…”