Raúl González-Núñez,  Gabriel Martinez,  Nelson Ricardo Avila-Rovelo,  Kyeog-Im Hong,  Amparo Ruiz-Carretero and  Rocío Ponce Ortiz  

In this work, we show that hydrogen bond interactions, in addition to directing supramolecular order, can have an intriguing effect on the molecular and electronic properties of DPP derivatives, facilitating redox processes in the solid state. As a result, charge carrier formation can be enhanced in devices, contributing to the improvement of electrical performances of two exceptionally small molecular semiconductors based on a thiophene-capped diketopyrrolopyrrole (DPP) as the electroactive component and amide groups as hydrogen-bonding units. Two different topologies of the amide groups were explored, C-centered and N-centered (HDPPBA-C and HDPPBA-N, respectively), and the results were compared to the HDPPH molecule with no amide groups. Spectroelectrochemical experiments, in conjunction with vibrational spectroscopies and DFT calculations, demonstrate that hydrogen bond formation promotes modifications on the effective conjugation length of the studied semiconductors, which may facilitate the generation of free charge carriers in organic field effect transistors (OFETs). These results open a new strategy towards the simple design of organic semiconductors and control over their morphological and electrical properties by simple hydrogen bond formation.

Olivier Bardagot, Brandon T. DiTullio, Austin L. Jones, Justin Speregen, John R. Reynolds, Natalie Banerji

The development of devices based on organic electrochemical transistors (OECTs) relies on the rational design of high-performing organic mixed ionic-electronic conductors (OMIECs). Here, a series of solution-processable copolymers composed of unsubstituted 2,2′-bis-(3,4-ethylenedioxy)thiophene (biEDOT) and 3,4-propylenedioxythiophene (ProDOT) substituted with linear or branched oligo(ethylene oxy) (OE) side chains are reported. By varying the size of the linear and branched side chains, it is found that the highest OECT performance is achieved with a near equivalent molar mass of the side chain and electroactive conjugated polymer repeat unit. With four OE units (PE₂-OE_4,electroactive content of 49%), OECTs with state-of-the-art normalized transconductance (453 ± 70 S cm⁻¹) and µC* (830 ± 37 F cm⁻¹ V⁻¹ s⁻¹), rapid dedoping kinetics, and a pulsing stability of 99% I_DS retention over 200 ON/OFF cycles are achieved. A consistent improvement in OECT stability with decreasing side-chain size is also observed. The origin of the enhanced stability is rationalized by correlating I_DS losses to changes in channel absorbance cycle after cycle during operation. This work encourages the calculation of the electroactive polymer content of an OMIEC when designing the side chains. It also shows that the PE₂ backbone with short OE side chains is a promising structure for (bio)electrochemical devices.