The Effect of Ring Expansion in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors

Abstract

A fused donor, thienobenzo [b]indacenodithiophene (TBIDT), was designed and synthesized using a novel acid-promoted cascade ring closure strategy, and copolymerized with a benzothiadiazole (BT) monomer. The backbone of TBIDT is an extension of the well-known indacenodithiophene (IDT) unit and was expected to enhance the charge carrier mobility, by improving backbone planarity and facilitating short-contacts between polymer chains. However, the optimized field-effect transistors demonstrated an average saturation hole mobility of 0.9 cm 2 V −1 s −1 , lower than the performance of IDT-BT (~1.5 cm 2 V −1 s −1 ). Mobilities extracted from time-resolved microwave conductivity (TRMC) measurements were consistent with the trend in hole mobilities in OFET devices. Scanning Tunneling Microscopy (STM) measurements and computational modelling illustrated that TBIDT-BT exhibits a less ordered microstructure in comparison to IDT-BT. This reveals that a regular side chain packing density, independent of conformational isomers, is critical to avoid local free volume due to irregular packing, which can host trapping impurities. DFT calculations indicated that TBIDT-BT, despite containing a larger, planar unit, showed less stabilization of planar backbone geometries, in comparison to IDT-BT. This is due to the reduced electrostatic stabilizing interactions between the peripheral thiophene of the fused core with the BT unit, resulting in a reduction of the barrier to rotation around the single bond. These insights provide a greater understanding of the general structure-property relationships required for semiconducting polymer repeat units to ensure optimal backbone planarization, as illustrated with IDT-type units, guiding the design of novel semiconducting polymers with extended fused backbones for high-performance field-effect transistors.

Novel cost-effective acceptor:P3HT based organic solar cells exhibiting the highest ever reported industrial readiness factor

“…1A. The core molecules were synthesized according to literature [25][26][27][28] after which Knoevenagel condensation between 3-ethylrhodanine and the dialdehyde functionalized core molecules were utilized to obtain the designed electron acceptors with a yield of 71.6%, 50.0%, 37.8%, and 60.1% for A1, A2, A3, and A4, respectively, further synthetic details can be seen in supporting information as well as molecular characterization (NMR Fig. S7 and MS Fig.…”

The impact of [1,2,5]chalcogenazolo[3,4‐f]‐benzo[1,2,3]triazole structure on the optoelectronic properties of conjugated polymers

“…Long alkyl chains are generally inserted to the polymer backbone resulting in high‐molecular‐weight polymers hence, extended electronic absorption. Polymers having those units are promising candidates for several applications like organic solar cells and OFETs, due to their excellent optoelectronic properties like high electron–hole mobilities, air stability, suitable energy levels via easy chemical modification, low cost, and low band gap. Additionally, the interaction between donor and acceptor units are remarkably affected by conjugated linkers and hence the optical, electrochemical, charge transport and photovoltaic properties of D–π–A conjugated copolymers are enhanced.…”

Linking Glass‐Transition Behavior to Photophysical and Charge Transport Properties of High‐Mobility Conjugated Polymers

“…Expanding on the design motif of C 16 IDT‐BT, a series of structurally similar near‐amorphous D–A copolymers were also investigated. These polymers exhibit further extended and rigidified donor units, including naphthacenodithiophene (NDT), [ 69 ] thienobenzo [b]indacenodithiophene (TBIDT), [ 70 ] and dithiopheneindenofluorene (TIF). [ 71 ] The underlying electronic design motive for these polymers is to facilitate polaron delocalization along the extended backbone and thus, further improve on the overall charge transport properties.…”