The continuous fiber networks with a balanced bimodal orientation of P(NDI2OD-T2) by controlling solution nucleation and face-on and edge-on crystallization rates

Tuning the nanostructure and molecular orientation of high molecular weight diketopyrrolopyrrole-based polymers for high-performance field-effect transistors

“…To the best of our knowledge, this is the first time that the film orientation of a DPP polymer can be tuned using the solvent quality strategy, in spite of a few examples for other polymer systems. 17,47,48 Further efforts are required to understand the origin of such orientation transitions. When the desired edge-on arrangement is induced by CB, the performance of a PDPP3T transistor is noticeably enhanced, with a hole mobility of 2.12 cm 2 V −1 s −1 and an on/off ratio of 10 8 .…”

From Solution to Thin Film: Molecular Assembly of π-Conjugated Systems and Impact on (Opto)electronic Properties

“…Nahid and McNeill et al have also shown that decreasing the solvent quality leads to a higher degree of edge-on orientation of P­(NDI2OD-T2) at the air/film interface: as revealed by NEXAFS measurements, the average backbone tilt angles with respect to the substrate increase from ∼60° for good solvents (xylene:1-chloro­naphthalene mixture and DCB) to ∼62°–63° for solvents with intermediate quality (chlorobenzene and chloroform), and eventually to ∼67° for poor solvents (toluene and xylene) . Wang and Han et al have found that P­(NDI2OD-T2) films spin coated from chloroform solution show a mixed orientation, whereas the edge-on content progressively increases from 38% to 54% upon adding 4 vol % ethylene glycol (considered as a poor solvent) into the solution . Taken together, these works suggest that enhancing the extent of solution-state aggregation is conducive to forming or increasing the extent of edge-on orientation in the corresponding films.…”

“…15 In some cases, a face-on/edge-on bimodal orientation is preferable due to the formation of threedimensional charge-transport pathways that efficiently boost transistor performance. 62,65−70 As we shall discuss in Section 2, tuning solution-state aggregation enables delicate control over the face-on/edge-on ratio, 15,17,67,71 which can potentially lead to an optimal bimodal distribution. 67 On the other hand, a preferential face-on orientation is desirable for devices requiring high levels of out-of-plane transport, such as OSCs (detailed in Section 1.2) and light emitting diodes.…”

“…15 In addition to film alignment and crystallinity, solution-state aggregation has a significant impact on the molecular orientation. 15,17,18,62,67,71 A notable work done by Li, Mullen, and Pisula et al has shown that the molecular orientation of difluorobenzothiadiazole (FBT)-based polymers can be tuned by controlling their solution aggregation. 18 When dissolved in chloroform, the polymers aggregate into 1-D fiber-like structures as evidenced by AFM imaging on drop-cast samples.…”

“…62,65−70 As we shall discuss in Section 2, tuning solution-state aggregation enables delicate control over the face-on/edge-on ratio, 15,17,67,71 which can potentially lead to an optimal bimodal distribution. 67 On the other hand, a preferential face-on orientation is desirable for devices requiring high levels of out-of-plane transport, such as OSCs (detailed in Section 1.2) and light emitting diodes. 63 At larger length scales (hundreds of nanometers to micrometers), charge transport can benefit from long-range ordering, where uniaxially aligned polymers adopt a rigid conformation.…”