Impact of hydrophilic side chains on the thin film transistor performance of a benzothieno-benzothiophene derivative

Side-chain engineering in molecular semiconductors provides a versatile toolbox for precisely manipulating the material's processability, crystallographic properties, as well as electronic and optoelectronic characteristics. This study explores the impact of integrating hydrophilic side chains, specifically oligoethylene glycol (OEG) units, into the molecular structure of the small molecule semiconductor, 2,7-bis(2(2-methoxy ethoxy)ethoxy) benzo[b]benzo[4,5] thieno[2,3-d] thiophene (OEG-BTBT). The investigation includes a comprehensive analysis of thin film morphology and crystallographic properties, along with the optimization of deposition parameters for improving the device performance. Despite the anticipated benefits, such as enhanced processability, our investigation into OEG-BTBT-based organic field-effect transistors (OFETs) reveals suboptimal performance marked by a low effective charge carrier mobility, a low on/off ratio, and a high threshold voltage. The study unveils bias stress effects and device degradation attributed to the high ionization energy of OEG-BTBT alongside the hydrophilic nature of the ethylene-glycol moieties, which lead to charge trapping at the dielectric interface. Our findings underscore the need for a meticulous balance between electronic properties and chemical functionalities in molecular semiconductors to achieve stable and efficient performance in organic electronic devices.

Highly crystalline and fluorescent BODIPY-labelled phenyl-triazole-coumarins as n-type semiconducting materials for OFET devices

In this work, the synthesis of BODIPY-phenyl-triazole labelled coumarins (BPhTCs) using a two-step approach is described. The influence of the BODIPY appending on the photophysical, electrochemical and thermal properties of the phenyl-triazole-coumarin precursors (PhTCs) was investigated. Band gap energies were measured by absorption spectroscopy (2.20 ± 0.02 eV in the solid and 2.35 ± 0.01 eV in solution) and cyclic voltammetry (2.10 ± 0.05 eV). The results are supported by DFT calculations confirming the presence of lowest LUMO levels that facilitate the electron injection and stabilize the electron transport. Their charge-transport parameters were measured in Organic Field-Effect Transistor (OFET) devices. BPhTCs showed an ambipolar transistor behavior with good n-type charge mobilities (10-2 cm2V-1s-1) allowing these derivatives to be employed as promising semiconducting crystalline and fluorescent materials with good thermal and air stability up to 250 °C.

BODIPY dyads and triads: synthesis, optical, electrochemical and transistor properties

A series of D–A dyads and D–A–D triads molecular systems based on triphenylamine and 9-ethyl-carbarzole as donor (D) and BODIPY as acceptor (A) has been designed and synthesized. The optoelectronic properties including optical, electrochemical, and charge carrier mobility of these molecules have been investigated. We found that the D–A–D triads exhibited broader absorption, raising the HOMO energy levels and increase hole carrier mobilities. Analysis surface morphology revealed that BODIPY containing carbazole demonstrated smooth film and no macro phase aggregation was observed upon thermal annealing.