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Influences of non-fullerene acceptor fluorination on three-dimensional morphology and photovoltaic properties of organic solar cells

DOI: 10.1021/acsami.9b07317 DOI Help

Authors: Mengxue Chen (Wuhan University of Technology) , Dan Liu (Wuhan University of Technology) , Wei Liu (Wuhan University of Technology) , Robert S. Gurney (Wuhan University of Technology) , Donghui Li (Wuhan University of Technology) , Jinlong Cai (Wuhan University of Technology) , Emma L. K. Spooner (University of Sheffield) , Rachel C. Kilbride (University of Sheffield) , James D. Mcgettrick (Swansea University) , Trystan M. Watson (Swansea University) , Zhe Li (Cardiff University) , Richard A. L. Jones (University of Sheffield) , David G. Lidzey (University of Sheffield) , Tao Wang (Wuhan University of Technology)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Applied Materials & Interfaces

State: Published (Approved)
Published: June 2019
Diamond Proposal Number(s): 20419

Abstract: Fluorination of conjugated molecules has been established as an effective structural modification strategy to influence properties, and has attracted extensive attention in organic solar cells (OSCs). Here, we have investigated optoelectronic and photovoltaic property changes of OSCs made of polymer donors with the non-fullerene acceptors (NFAs) ITIC and IEICO and their fluorinated counterparts IT-4F and IEICO-4F. Device studies show that fluorinated NFAs lead to reduced Voc but increased Jsc and FF, and therefore the ultimate influence to efficiency depends on the compensation of Voc loss and gains of Jsc and FF. Fluorination lowers energy levels of NFAs, reduces their electronic bandgaps and red-shifts the absorption spectra. The impact of fluorination on the molecular order depends on the specific NFA, with the conversion of ITIC to IT-4F reduces structural order, which can be reversed after blending with the donor PBDB-T. Contrastingly, IEICO-4F presents stronger π−π stacking after fluorination from IEICO, and this is further strengthened after blending with the donor PTB7-Th. The photovoltaic blends universally present a donor-rich surface region which can promote charge transport and collection towards anode in inverted OSCs. The fluorination of NFAs, however, reduces the fraction of donors in this donor-rich region, consequently encourage the intermixing of donor/acceptor for efficient charge generation.

Journal Keywords: organic solar cells; non-fullerene acceptors; fluorination; three-dimensional morphology; photovoltaic properties

Subject Areas: Materials, Energy


Instruments: I07-Surface & interface diffraction