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

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 pi-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 PBDTbiTPD(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 shortcircuit current, despite the slightly decreased VOC compared to that of PBDT-biTPD(HD):PC71BM.

Automated summary

Thienopyrroledione (TPD) derivatives were designed and synthesized as electron-accepting core building blocks for high-performance organic photovoltaic (OPV) cells. The synthesized copolymers showed broad absorption and low frontier molecular orbital energy levels. The OPV devices exhibited high power conversion efficiency (PCE), with the best performance achieved by PBDT-biTPD(HD):IT-4F.