Very few studies have reported oriented crystallization of conjugated polymers directly in solution. Here, solution crystallization of conjugated polymers in a microfluidic system is found to produce tightly π-stacked fibers with commensurate improved charge transport characteristics. For poly(3-hexylthiophene) (P3HT) films, processing under flow caused exciton bandwidth to decrease from 140 to 25 meV, π-π stacking distance to decrease from 3.93 to 3.72 Å and hole mobility to increase from an average of 0.013 to 0.16 cm(2) V(-1) s(-1), vs films spin-coated from pristine, untreated solutions. Variation of the flow rate affected thin-film structure and properties, with an intermediate flow rate of 0.25 m s(-1) yielding the optimal π-π stacking distance and mobility. The flow process included sequential cooling followed by low-dose ultraviolet irradiation that promoted growth of conjugated polymer fibers. Image analysis coupled with mechanistic interpretation supports the supposition that "tie chains" provide for charge transport pathways between nanoaggregated structures. The "microfluidic flow enhanced semiconducting polymer crystal engineering" was also successfully applied to a representative electron transport polymer and a nonhalogenated solvent. The process can be applied as a general strategy and is expected to facilitate the fabrication of high-performance electrically active polymer devices.

A new solution-processable small-molecule containing electron-poor naphthalene diimide and tetrazine moieties has been synthesized. The optimized spin-coated n-channel OFETs on glass substrate shows electron mobility value up to 0.15 cm(2) V(-1) s(-1) . Inkjet-printed OFETs are fabricated in ambient atmosphere on flexible plastic substrates, which exhibits an electron mobility value up to 0.17 cm(2) V(-1) s(-1) and also shows excellent environmental and operational stability.

Since being introduced to the open literature in 2010, the isoindigo heterocycle has been extensively studied as a novel electron-deficient building block for organic electronic materials in conjugated polymers, discrete length oligomers, and molecular systems, particularly targeting high charge mobility values and ambipolar transport in organic field effect transistors, along with high power conversion efficiencies in organic photovoltaic devices. This article introduces results obtained on copolymers of isoindigo with thiophene and alkylated terthiophenes to highlight fundamental characteristics in isoindigo-based polymers and the resulting organic field-effect transistors and photovoltaic devices. By comparing and contrasting the optoelectronic properties, thin film morphology, organic field-effect transistor (OFET) mobilities, and organic photovoltaic (OPV) performance to previously reported polymers, structure–processing–property relationships were uncovered. In particular, isoindigo-containing polymers with more rigid backbones and higher coherence lengths in thin films lead to increased charge mobility in OFET devices. In OPV devices, efficiencies over 6% can be obtained by balancing high ionization potentials typically dictating the open-circuit voltage and the charge transfer energy, and blend morphology impacting short-circuit currents. Furthermore, the impact of polymer structure on solubility and on phase separation in blends with PC71M is discussed, with isoindigo-based polymers exhibiting lower solubility possibly leading to more fiber-like morphologies stemming either from polymer dissolution in the casting solvent or from polymer self-assembly during film formation. This fiber-like polymer morphology remains unaffected by the presence of processing additives, such as 1,8-diiodooctane. These structure–property relationships developed for isoindigo-based polymers can also be discussed in the broader context of diketo­pyrrolopyrrole (DPP) and thieno­isoindigo (TiI) as electron-deficient moieties that can also be doubly substituted on their amide functionality.

In this study, a highly soluble PCBM-based thermo-cross-linkable fullerene precursor has been synthesized for use in bulk heterojunction based organic solar cells. The cross-linking was achieved using a thermally activated benzocyclobutene (BCB) molecule. The thermo-crosslinking reaction is initiated at temperatures as low as 150 C. Compared to PCBM, the cross-linked fullerene is highly insoluble and has a diffusional mobility in poly(3-hexylthiophene) (P3HT) that is an order of magnitude slower than PCBM. Its electron mobility is comparable to that of PCBM and organic photovoltaic (OPV) devices consisting of bulk heterojunction active layers with P3HT or PTB7 and this fullerene show very similar efficiencies. Devices prepared either with pure cross-linked fullerene or its mixture with PCBM as acceptors in OPVs have been shown to be highly stable to accelerated aging with little loss in device efficiency up to 48 hours of aging at 150 C. This compares to a loss of 60% of initial efficiency in identically prepared devices when using PCBM as the acceptor. Optical microscopy and grazing incidence wide angle X-ray scattering (GIWAXS) shows that a probable cause for this excellent stability in the cross-linked fullerene containing BHJs is associated with a significant inhibition of formation of crystals of fullerene.