Nature and Extent of Solution Aggregation Determines the Performance of P(NDI2OD‐T2) Thin‐Film Transistors

Abstract

Here the effect of solvent quality on the microstructure and organic field-effect transistor (OFET) performance of thin films of the high mobility naphthalene-diimide-thiophene based n-type semiconducting copolymer P(NDI2OD-T2) is investigated. A strong correlation between OFET mobility and solvent quality is observed with average electron mobility increasing from 0.21 cm 2 /Vs for samples prepared from tolerably-good solvents to 0.56 cm 2 /Vs for samples prepared from poor solvents, with a maximum electron mobility of 1.5 cm 2 /Vs observed for transistors processed from toluene. The variation in transistor performance with solvent quality is linked to the nature and extent of the solution aggregation of P(NDI2OD-T2) chains. Small angle X-ray scattering measurements reveal elongated rod-like aggregates up to 300 nm in length in solutions prepared using poor solvents, in contrast to more coil-like chains with radius of gyration of ~ 10 to 15 nm for solutions based on good to tolerably-poor solvents. Thin films produced from decreasing solvent quality show an increase in the extent of correlated ordering of backbones and the degree edge-on orientation of polymer chains at the air/film interface. This work establishes the important link between solution-phase chain aggregation behavior, thin-film microstructure and transistor performance in the P(DNI2OD-T2) system.

Ordered Solid‐State Microstructures of Conjugated Polymers Arising from Solution‐State Aggregation

“…To demonstrate the temperature effect on polymer aggregation in solution, in situ SANS experiments were performed. [19,34,35] The strong temperature dependence of SANS data manifested that the conjugated polymer formed large aggregates in solution owing to their strong intermolecular interactions. [36] As the temperature increased from 30 to 80 8C, the scattering intensity at the low range of the scattering vector (Q) decreased evidently, indicating the large aggregates transited to small sizes.…”

“…Revealing the relationship between solution‐state aggregation and solid‐state microstructures is a crucial aspect of organic electronics. However, conjugated polymers usually form inter‐chain entanglement and complicated aggregates in solution owing to strong π–π interactions, making it difficult to probe, characterize, and control the solution‐state aggregation …”

“…However, conjugated polymers usually form inter-chain entanglement and complicated aggregates in solution owing to strong p-p interactions, making it difficult to probe, characterize, and control the solution-state aggregation. [17][18][19] Solution-state aggregation is a general phenomenon for conjugated polymers. However, directly controlling the solution-state aggregation of conjugated polymers remains a challenge due to the lack of adequate characterization and modulation methods.…”

Ladder-type bithiophene imide-based organic semiconductors: understanding charge transport mechanisms in organic field effect transistors

“…The aggregation processes play a very important role in the charge transport mechanism. [35][36][37] Therefore, understanding how these highly planar molecules organize in the solid state and how this affects the charge transfer processes and stabilization of charged states in organic thin-layers, could help us to shed light on charge transport mechanisms in electronic devices.…”

Controlling the Microstructure of Conjugated Polymers in High‐Mobility Monolayer Transistors via the Dissolution Temperature

“…Another efficient strategy for tuning polymer aggregation is to tune the solvent quality . For P(NDI2OD‐T2), tolerably poor solvents resulted in elongated rod‐like 300‐nm aggregates in solution and enhanced field‐effect mobility in thin films by a factor of 2.7 . However, solvents with different qualities typically lead to a large variation of boiling points and vapor pressures, greatly limiting solution processing.…”