Quinoxaline-Based Wide Band Gap Polymers for Efficient Nonfullerene Organic Solar Cells with Large Open-Circuit Voltages

Jie Yang, Mohammad Afsar Uddin, Yumin Tang, Yulun Wang, Yang Wang, Huimin Su, Rutian Gao, Zhi Kuan Chen, Junfeng Dai, Han Young Woo, Xugang Guo

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

We present here a series of wide-band-gap (E g : >1.8 eV) polymer donors by incorporating thiophene-flanked phenylene as an electron-donating unit and quinoxaline as an electron-Accepting co-unit to attain large open-circuit voltages (V oc s) and short-circuit currents (J sc s) in nonfullerene organic solar cells (OSCs). Fluorination was utilized to fine-Tailor the energetics of polymer frontier molecular orbitals (FMOs) by replacing a variable number of H atoms on the phenylene moiety with F. It was found that fluorination can effectively modulate the polymer backbone planarity through intramolecular noncovalent S···F and/or H···F interactions. Polymers (P2-P4) show an improved molecular packing with a favorable face-on orientation compared to their nonfluorinated analogue (P1), which is critical to charge carrier transport and collection. When mixed with IDIC, a nonfullerene acceptor, P3 with two F atoms, achieves a remarkable V oc of 1.00 V and a large J sc of 15.99 mA/cm 2 , simultaneously, yielding a power-conversion efficiency (PCE) of 9.7%. Notably, the 1.00 V V oc is among the largest values in the IDIC-based OSCs, leading to a small energy loss (E loss : 0.62 eV) while maintaining a large PCE. The P3:IDIC blend shows an efficient exciton dissociation through hole transfer even under a small energy offset of 0.16 eV. Further fluorination leads to the polymer P4 with increased chain-Twisting and mismatched FMO levels with IDIC, showing the lowest PCE of 2.93%. The results demonstrate that quinoxaline-based copolymers are promising donors for efficient OSCs and the fluorination needs to be fine-Adjusted to optimize the interchain packing and physicochemical properties of polymers. Additionally, the structure-property correlations from this work provide useful insights for developing wide-band-gap polymers with low-lying highest occupied molecular orbitals to minimize E loss and maximize V oc in nonfullerene OSCs for efficient power conversion.

Original languageEnglish
Pages (from-to)23235-23246
Number of pages12
JournalACS Applied Materials and Interfaces
Volume10
Issue number27
DOIs
Publication statusPublished - 2018 Jul 11

Keywords

  • energy losses
  • fluorination
  • nonfullerene organic solar cells
  • open-circuit voltages
  • polymer semiconductors

ASJC Scopus subject areas

  • Materials Science(all)

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