Silaindacenodithiophene-Based Fused-Ring Non-Fullerene Electron Acceptor for Efficient Polymer Solar Cells

In this work, a new A-D-A type nonfullerene small molecular acceptor SiIDT-IC, with a fused-ring silaindacenodithiophene (SiIDT) as D unit and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the end A unit, was design and synthesized. The SiIDT-IC film shows absorption peak and edge at 695 and 733nm, respectively. The HOMO and LUMO of SiIDT-IC are of -5.47 and -3.78eV, respectively. Compared with carbon-bridging, the Si-bridging can result in an upper-lying LUMO level of an acceptor, which is benefit to achieve a higher open-circuit voltage in polymer solar cells (PSCs). Complementary absorption and suitable energy level alignment between SiIDT-IC and wide bandgap polymer donor PBDB-T were found. For the PBDB-T:SiIDT-IC based inverted PSCs, a D/A ratio of 1: 1 was optimal to achieve a power conversion efficiency (PCE) of 7.27%. With thermal annealing (TA) of the blend film, a higher PCE of 8.16% could be realized due to increasing of both short-circuit current density and fill factor. After the TA treatment, hole and electron mobilities were elevated to 3.42x10(-4) and 1.02x10(-4) cm(2)V(-1)s(-1), respectively. The results suggest that the SiIDT, a Si-bridged fused ring, is a valuable D unit to construct efficient nonfullerene acceptors for PSCs.