A new isoindigo-based molecule with ideal energy levels for solution-processable organic solar cells

A new easily-accessible solution-processed oligomer, with an isoindigo group as an electron acceptor and a thieno[3,2-b]thiophene flanked by thiophenes as electron donors, has been synthesized by a Stille coupling reaction. Through introducing the extended π-conjugated groups into isoindigo, the electro-optical properties of the material can be fine-tuned. The isoindigo oligomer has a broad absorption in the region from 300 to 800 nm with a narrow bandgap (1.54 eV), which is believed to be an ideal bandgap as donor materials. The oligomer possesses low HOMO energy level (−5.39 eV). The potential of optical and electronic properties encouraged us to explore the photovoltaic performance using the oligomer as the donor material in bulk heterojunction organic solar cell along with 6,6-phenyl-C61-butyric acid methyl ester as the acceptor. The solar cell based on the oligomer with an inverted device configuration provided a power conversion efficiency of 1.41% under the AM 1.5G illumination with an intensity of 100 mW cm−2 from a solar simulator.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new isoindigo-based oligomer with extended conjugation was designed and synthesized. ► The oligomer showed low bandgap with 1.54 eV and low lying HOMO level with −5.39 eV. ► The inverted solar device with power conversion efficiency of 1.41% was obtained.