Interfacial electronic structure of Cl6SubPc non-fullerene acceptors in organic photovoltaics using soft X-ray spectroscopies

Hyunbok Lee, Sun Woo Ahn, Sim Hee Ryu, Bo Kyung Ryu, Myeung Hee Lee, Sang Wan Cho, Kevin E. Smith, Tim S. Jones

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Abstract

In organic photovoltaics (OPVs), determining the energy-level alignment of a donor and an acceptor is particularly important since the interfacial energy gap between the highest occupied molecular orbital (HOMO) level of a donor and the lowest unoccupied molecular orbital (LUMO) level of an acceptor (EDHOMO-EALUMO) gives the theoretical maximum value of the open-circuit voltage (VOC). To increase the EDHOMO-EALUMO, non-fullerene acceptors, which have a lower electron affinity (EA) than C60, are receiving increasing attention. In this study, we investigated the energy-level alignment at the interface of a boron chloride subphthalocyanine (SubPc) donor and a halogenated SubPc (Cl6SubPc) acceptor using soft X-ray spectroscopy techniques. The estimated EDHOMO-EALUMO of Cl6SubPc/SubPc was 1.95 eV, which was significantly higher than that of 1.51 eV found at the interface of C60/SubPc. This increased EDHOMO-EALUMO was the origin of the enhanced VOC in OPVs. Additionally, we studied the molecular orientation of Cl6SubPc using angle-dependent X-ray absorption spectroscopy. The highly disordered Cl6SubPc molecules result in low carrier mobility, which contributes to the lower short-circuit current density of the Cl6SubPc acceptor OPVs than the C60 acceptor OPVs.

Original languageEnglish
Pages (from-to)31628-31633
Number of pages6
JournalPhysical Chemistry Chemical Physics
Volume19
Issue number47
DOIs
Publication statusPublished - 2017 Jan 1

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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