Spirobifluorene-cored wide bandgap non-fullerene small molecular acceptor with 3D structure for organic solar cells

Abstract

In this paper, a wide bandgap small molecule (SF(BR)4) based on spirobifluorene (SF) core, which is flanked with 2,1,3-benzothiadiazole and end-capped with 3-ethylrhodanine groups is synthesized and investigated as a non-fullerene acceptor in solution-processed organic solar cells (OSCs). The SF(BR)4 shows a wide optical bandgap of 2.10 eV and great advantages with respect to the low bandgap donor material poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)2,2′; 5′,2″; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD), such as well energy-level matching and complementary absorption. Furthermore, the three dimensional (3D) molecular geometry of SF(BR)4 helps to suppress the strong intermolecular aggregation in PffBT4T-2OD:SF(BR)4 blend, leading to efficient non-fullerene OSCs. The resultant devices show a power conversion efficiency (PCE) of 6.15%. To our best knowledge, the PCE is among the highest reported to date for 3D non-fullerene acceptors except perylene diimides derivatives.