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

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.