Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains

National Research Fund of Luxembourg. Grant Number: 6932623; Croucher Foundation; Kodak Graduate Fellowship; Office of Naval Research. Grant Number: N00014-17-1-2214; U.S. Department of Energy. Grant Number: DE-AC02-76SF0051

Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains

The solid-state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high-performing diketopyrrolopyrrole-based polymers. By synthesizing a series of DPP-based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face-on/edge-on orientation, which allows the formation of 3D carrier channels in an otherwise edge-on-oriented polymer chain network. Time-of-flight measurements performed on the various polymer films support this hypothesis by showing higher out-of-plane carrier mobilities for the partially face-on-oriented polymers. Additionally, a favorable morphology is mimicked by blending a face-on polymer into an exclusively edge-on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices

Dynamic organic lens using photosensitive semiconductor (P3HT:PCBM) for millimetre-wave applications

© 2017 IEEE. A WR-3 waveguide band dynamic organic lens has been designed and its performance analysed using the CST Studio Suite software. In order to determine the dynamic behaviour of the lens, the patterned distribution of the electron-hole pairs in the photo-active region of the organic lens was input to the software, as a change in the complex permittivity. The dielectric response of the organic polymer (P3HT:PCBM), both in the presence (active state) and absence (dark state) of illumination (60±5 mW/cm 2 ), was estimated using a quasi-optic bench for the intended WR-3 frequency domain operation. The spatial-distribution of the phase of the electric field between dark and active states of the organic lens was determined as a proof-of-concept of the dynamic operation of the lens