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

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 nonfullerene 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-octyldodecy1)2,2'; 5 '',2 '''-quaterthiophen-5,5 '''-diy1)] (PffBT4T-20D), 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-20D: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.