Interplay of Molecular Orientation, Film Formation, and Optoelectronic Properties on Isoindigo- and Thienoisoindigo-Based Copolymers for Organic Field Effect Transistor and Organic Photovoltaic Applications

A systematic study on the effects of heteroarenes on the solid state structure and optoelectronic properties of isoindigo analogues, namely, PBDT-IIG and PBDT-TIIG, used in solution-processed organic field effect transistors (OFETs) and organic photovoltaics (OPVs) is reported. We discover that the optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, solubility, film morphology, charge carrier mobility, and solar cell performance are critically influenced by the heteroarenes in the acceptor subunits. PBDT-IIG exhibits good p-type OFET performance with mobility up to 1.03 × 10–1 cm2 V–1 s–1, whereas PBDT-TIIG displays ambipolar mobilities of μh = 7.06 × 10–2 cm2 V–1 s–1 and μe = 2.81 × 10–4 cm2 V–1 s–1. PBDT-IIG and PBDT-TIIG blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) yield promising power conversion efficiencies (PCEs) of 5.86% and 2.55%, respectively. The excellent mobility of PBDT-IIG can be attributable to the growing fraction of edge-on packing by t...