Controlling Structural and Energetic Disorder in High-Mobility Polymer Semiconductors via Doping with Nitroaromatics
Pegah Ghamari, Muhammad Rizwan Niazi, Dmitrii F. Perepichka
Abstract
Molecular doping has emerged as a powerful strategy to tune the charge transport properties of organic field-effect transistors (OFETs). However, the limited tool-box of molecular dopants and unresolved challenges of stability, uniformity of the doping, and matching the energy levels constrain the achieved OFET device performance and thwart the practical applications. Here, nitrofluorene (NF) acceptors are introduced as effective p-dopants in polymer OFETs, resulting in outstanding device performance of a standard commercial diketopyrrolopyrrole-thienothiophene (DPP-DTT) polymer. An ∼5-fold enhancement in the saturation field-effect mobility (up to ∼8 cm2 V–1 s–1) is realized in ambient air operations after doping with 2,4,5,7-tetranitrofluorenone. Importantly, the achieved effective mobility (which accounts for device nonideality) exceeds 6 cm2 V–1 s–1, which is among the highest values reported for polymer OFETs. The spectroscopic, microscopic, X-ray diffraction, and electrical investigations elucidate the role of NF dopants in mitigating charge carrier traps, lowering the contact resistance, and maximizing the structural order of the polymer films. Energetic disorder reduces significantly upon doping as revealed via variable temperature mobility measurements.