4.8 Article

Overcoming incompatibility of donors and acceptors by constructing planar heterojunction organic solar cells

Journal

NANO ENERGY
Volume 85, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.nanoen.2021.105957

Keywords

Organic solar cells; Planar heterojunction structure; Layer-by-layer processing; Film morphology

Funding

  1. Guangdong Major Project of Basic and Applied Basic Research of China [2019B030302007]
  2. National Key Research and Development Program of China - MOST of China [2019YFA0705901]
  3. National Natural Science Foundation of China [21905103, 21822505]
  4. U.S. Office of Science, U.S. Office of Basic Energy Sciences, of the U.S. Department of Energy

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Research demonstrates that utilizing quasi-orthogonal solvents in traditional planar heterojunction structures can overcome limitations of nanoscale phase separation in bulk-heterojunction organic solar cells, leading to an improved power conversion efficiency of 14.2%. Additional experiments confirm the key factors in forming optimal nanoscale morphology.
Nanoscale phase separation plays a critical role in achieving high photovoltaic performance in bulkheterojunction organic solar cells, which is limited by solubility, crystallinity, and the compatibility of the donors and acceptors. However, these limits can be overcome by new applications of the traditional planar heterojunction structure. Herein, we demonstrate quasi-orthogonal solvents for a wide-band-gap donor (P2F-EHp) and a highly crystalline non-fullerene acceptor (M4-4F) to overcome the over-agglomeration and enabled the fabrication of a planar heterojunction device with a favorable power conversion efficiency of 14.2% (compared with 12.7% in bulk-heterojunction device), which is among one of the highest efficiencies of planar heterojunction devices to date. Detailed studies based on cross-sectional transmittance electron microscopy, grazing incidence wide-angle X-ray scattering at various incident angles, and resonance soft X-ray scattering measurements confirmed the formation of optimal nanoscale morphology. Further transient absorption measurements also proved that the exciton dissociation and free-carrier generation efficiency are not limited by the small mixed-phase area and large pure domains. These findings show insights into the intrinsic morphological changes and charge transfer process in bulk-heterojunction and planar heterojunction structures, providing a novel method for matching donors and acceptors with relatively poor compatibility.

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