Ethanol-Processable, Highly Crystalline Conjugated Polymers for Eco-Friendly Fabrication of Organic Transistors and Solar Cells

Abstract

We report eco- and human-friendly fabrication of organic field-effect transistors (OFETs) and polymer solar cells (PSCs) using only ethanol as a processing solvent at ambient condition, in stark contrast to that involving the use of halogenated and/or aromatic solvents. New ethanol-processable electroactive materials, p-type polymer (PPDT2FBT-A) and n-type bis-adduct fullerene acceptor (Bis-C-60-A) are designed rationally by incorporation of oligoethylene glycol (OEG) side-chains. By ethanol processing, PPDT2FBT-A shows a broad light absorption in the range of 300-700 nm and highly crystalline interchain ordering with out-of-plane interlamellar scattering up to (400) with strong pi-pi stacking. As a result, the ethanol-processed PPDT2FBT-A OFETs yield high charge-carrier mobilities up to 1.0 x 10(-2) cm(2) s(-1), which is the highest value reported to date from alcohol-processed devices. Importantly, the ethanol-processed PPDT2FBT-A OFET outperformed that processed using typical processing solvent, chlorobenzene (CB), with similar to 10-fold enhancement in hole mobility, because the highly edge-on oriented packing of PPDT2FBT-A was produced by ethanol-process. Also, for the first time, significant photovoltaic performance was achieved for the ethanol-processed device of PPDT2FBT-A and Bis-C-60-A due to the formation of an interpenetrating nanofibrillar morphology of highly crystalline PPDT2FBT-A polymers. The relationships between molecular structure, nanoscale morphology and electronic properties within ethanol-processed OFETs and PSCs were elucidated by comparing to typical CB-processed devices. These comparisons provide important guidelines for the design of new ethanol/water-soluble active layer materials and their use in the development of green solvent-processed efficient OFETs and PSCs.