Bithienopyrroledione-based polymeric donors for efficient fullerene- and non-fullerene-based organic photovoltaic cells

Abstract

Thienopyrroledione (TPD) is a promising electron-accepting core building block of donor-acceptor-type semiconducting polymers for use in high-performance organic photovoltaic (OPV) cells. In this study, bithienopyrroledione (biTPD) derivatives with different lengths of side alkyl chains were designed to utilize specific ability including stronger electron-withdrawing strength and extended π-conjugation compared with the mono TPD unit. The synthesized copolymers, poly(3-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-6-octylthieno[3,2-b]thiophen-2-yl)-5,5′-bis(2-butyloctyl)-3'-(6-octylthieno[3,2-b]thiophen-2-yl)-4H,4′H-[1,1′-bithieno[3,4-c]pyrrole]-4,4′,6,6′(5H,5′H)-tetraone) (PBDT-biTPD(BO)) and poly(3-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-6-octylthieno[3,2-b]thiophen-2-yl)-5,5′-bis(2-hexyldecyl)-3'-(6-octylthieno[3,2-b]thiophen-2-yl)-4H,4′H-[1,1′-bithieno[3,4-c]pyrrole]-4,4′,6,6′(5H,5′H)-tetraone) (PBDT-biTPD(HD)), composed of biTPD and typical benzo[1,2-b:4,5-b’]dithiophene (BDT) units had broad absorption with deep frontier molecular orbital energy levels. In addition, PBDT-biTPD(BO) and PBDT-biTPD(HD) showed predominant face-on orientation confirmed by the grazing-incidence wide-angle X-ray scattering (GIWAXS). The OPV device exhibited the maximum power conversion efficiency (PCE) of 8.48% and 8.99% for PBDT-biTPD(BO):PC71BM and PBDT-biTPD(HD):PC71BM, respectively, with a high open-circuit voltage (VOC). In particular, PBDT-biTPD(HD):IT-4F showed the best PCE of 9.49% with improved short-circuit current, despite the slightly decreased VOC compared to that of PBDT-biTPD(HD):PC71BM.