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Molecular Engineering for Large Open-Circuit Voltage and Low Energy Loss in Around 10% Non-fullerene Organic Photovoltaics

  • Author(s): He, B
  • Yang, B
  • Kolaczkowski, MA
  • Anderson, CA
  • Klivansky, LM
  • Chen, TL
  • Brady, MA
  • Liu, Y
  • et al.
Abstract

Recent efforts in organic photovoltaics (OPVs) have been devoted to obtaining low-bandgap non-fullerene acceptors (NFAs) for high photocurrent generation. However, the low-lying lowest unoccupied molecular orbital (LUMO) level in narrow bandgap NFAs typically results in a small energy difference (ΔE ) between the LUMO of the acceptor and the highest occupied molecular orbital (HOMO) of the donor, leading to low open-circuit voltage (V ). The trade-off between ΔE and photocurrent generation significantly limits the simultaneous enhancement of both V and short-circuit current density (J ). Here, we report a new medium-bandgap NFA, IDTT-T, containing a weakly electron-withdrawing N-ethyl thiabarbituric acid terminal group on each end of the indacenodithienothiophene (IDTT) core. When paired with a benchmark low-bandgap PTB7-th polymer donor, simultaneous enhancement of both ΔE and absorption spectral coverage was realized. The OPV devices yield a V of 1.01 V, corresponding to a low energy loss of 0.57 eV in around 10% efficiency single-junction NFA OPVs. The design demonstrates a working principle to concurrently increase ΔE and photocurrent generation for high V and PCE in bulk fullerene-free heterojunction OPVs. DA OC DA OC SC DA OC DA OC

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