Tunable Charge Transport Using Heterocycles-Flanked Alkoxyphenanthrenes for High-Performing OFETs

Abstract

A series of new heterocycles-flanked alkoxyphenanthrenes with D′-D-D′ and A-D-A architecture was synthesized for high-performance solution-processable p-channel, n-channel, and ambipolar organic field-effect transistors. The impact of electron-donating and -accepting abilities of the sulfur- and nitrogen-containing heteroaromatics on photophysical, electrochemical, and semiconducting properties was analyzed. The presence of heteroaryl rings improves the extended conjugation, two-dimensional lattices of π–π stacks, and increased molecular interaction of the functionalized phenanthrenes (PN) to allow better self-assembly. The electronically dynamic PN self-assembles into continuous microdomains, forming percolation channels for holes, electrons, or both reliant on functionalization. The low-lying LUMO levels of the compounds enabled ambipolar transport and reduced energy levels for charge injections. Spin-coated devices fabricated using functionalized PN with sulfur-containing heteroaryl substituted PN exhibited the highest hole mobility of 0.85 cm²/(V s) with 10⁸ on/off current ratio. Compounds with A-D-A architecture showed n-channel/ambipolar charge transport, especially napthalimide acceptor substituted PN exhibited n-channel electron mobility of 0.78 cm²/(V s) and an on/off ratio of 10⁶. X-ray diffraction and scanning electron microscopy studies further delineate the impact of efficient packing in the film. Quantum chemistry calculations combined with Marcus–Hush electron transfer theory interpret the transport parameters, and heteroatoms are established to impact the charge mobility intensely.