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A New Wide Band Gap Donor for Efficient Fullerene-free All-small-molecule Organic Solar Cells.

ABSTRACT

A new organic small molecule, DRTB-T, that incorporates a two-dimensional tri-alkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (Egopt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. Non-fullerene small-molecule solar cells consisting of DRTB-T and a non-fullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (Voc = 0.98 V). This is the highest PCE for a non-fullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) non-fullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.