Tuning Frontier Orbital Energetics of Azaisoindigo‐Based Polymeric Semiconductors to Enhance the Charge‐Transport Properties

Abstract

Crucial to the development of polymeric semiconductors has been the establishment of structure-property correlations to achieve high-mobility and versatile devices. [2] Despite the continuing improvement of carrier mobilities, a clear understanding of charge transport mechanisms and the relationship between device function and molecular structure are yet to be fully explored. Thanks to the thirdgeneration donor-acceptor (D-A) alternating conjugated copolymers, tunable comonomers are able to be incorporated into the backbone, evolving in the diversity and complexity to deeply investigate the influencing factors. [3] Coplanarity, π-conjugation, linearity, symmetry, frontier molecular orbital (FMO) energy, heteroatom effect, molecular weight, and density of side chains, to name but a few, are usually deemed critical in the structural and conformational control for rational design of conjugated polymers. When attempting to gain insight into these sophisticated factors, one might select a state-of-the-art building block and adjust the other moiety to fine-tune electronic and solid-state structures. A delicate compromise between such factors is also needed to achieve the optimal device performance. [4] Exploring new structures to boost device performance has always been the motivation of synthetic scientists. [1c,h,5] During the past few years, bislactam or bisimide has emerged as electron-withdrawing building blocks for high-performance semiconductors. For example, field-effect transistors of diketopyrrolopyrrole-, isoindigo-, and naphthalenediimide-based polymeric semiconductors exhibit mobilities of 1-10 cm 2 V −1 s −1 , which are comparable to inorganic counterparts. [1c,d] The incorporation of bislactam or bisimide provides three major advantages: (a) the electron deficient nature of these functional groups lowers the FMO energy levels to stabilize injected charge carriers and enhances stacking interactions between π-orbitals by depleting electron density and subsequently relieving electrostatic repulsion; [6] (b) the presence of intramolecular throughspace interactions minimizes dihedral torsions and promotes backbone coplanarity; [1c] (c) readily introduced side chains can not only tune the polymer aggregation tendency but also ensure solution processability. [3b] Among these bislactam-orTo establish a structure-property relationship between polymer backbone structures and field-effect transistor performance has emerged as a new topic in organic electronics. The tunability and diversity of organic semiconductors provide the feasibility of controlling the electrical properties. Herein the characterization of thienothiophene-, dithiophenylethene-, biselenophene-, and diselenophenylethene-containing azaisoindigo copolymers is presented. As suggested by both theoretical calculations and experimental results, backbone electronic structure and linearity, density of side chains, aggregation, and thin film microstructure are involved in the differences in optical and electrical properties of these polymers. As...

Revealing Donor–Acceptor Interaction on the Printed Active Layer Morphology and the Formation Kinetics for Nonfullerene Organic Solar Cells at Ambient Conditions

“…The slight red shifts for the PDTBT2T-FTBDT films printed from CF solvent could be a head-to-tail aggregation preference in comparison with the CB solvent. [34] Unlike the neat PDTBT2T-FTBDT thin film, the CB processed BTP-4F blend film exhibits an absorption peak at 859 nm, which blue shifts to 835 nm in case of printing out of CF solvent. This behavior results from a pronounced H-aggregate tendency with a side-by-side arrangement in the CF processed neat BTP-4F film.…”

Recent Advances in Isoindigo‐Inspired Organic Semiconductors

“…de Miguel et al. reported the synthesis and characterization of 7,7′‐diazaisoindigo, and two separate research groups incorporated this structure into donor‐acceptor polymers . Huang et al.…”

“…reported a copolymer of diazaisoindigo and bithiophene ( 20 ) (Chart 3), which exhibited high and balanced hole and electron mobilities (Table ) . Following this, the group went on to synthesize a series of diazaisoindigo copolymers with biselenophene ( 21 ), thienothiophene ( 22 ), dithienylethene ( 23 ), and diselenophenylethene ( 24 ) donor units (Chart 3) . The optoelectronic properties and OFET performance of these polymers are summarized in Table .…”

Rational Design of Highly Soluble and Crystalline Conjugated Polymers for High‐Performance Field‐Effect Transistors

“…In addition, PCD3 also showed more distinct vibrational bands (794 and 859 nm) in the ICT band region than PCD1 and PCD2, which is indicative of coplanarity and strong aggregation. [23,27] The frontier orbital energy levels and optical bandgaps of the polymers were extracted from the cyclic voltammetry (CV) curves (Figure 2d) along with the ultraviolet-visible-near infrared (UV-vis-NIR) absorption spectra. First, optical bandgaps were evaluated from the Tauc plots of the polymers in the film state with their UV-vis-NIR absorption spectra (Figure S14, Supporting Information).…”