The performance of photovoltaic devices based on blends of conjugated polymers with non-fullerene acceptors depends upon the phase behaviour and microstructure of the binary, which in turn depends on the chemical structures of the molecular components and the blend composition. We investigate the correlation between molecular structure, composition, phase behaviour and device performance of a model system comprising semi-crystalline poly-3-hexylthiophene (P3HT) as the donor polymer and three non-fullerene acceptors, two of which (O-IDTBR/EH-IDTBR) have a planar core with different side-chains, and one (O-IDFBR) has a twisted core. We combine differential scanning calorimetry with optical measurements including UV-Vis, photoluminescence, spectroscopic ellipsometry and Raman, and photovoltaic device performance measurements, all at varying blend composition. For P3HT:IDTBR blends, the crystallinity of polymer and acceptor are preserved over a wide composition range and the blend displays a eutectic phase behaviour, with the optimum solar cell composition lying close to the eutectic. For P3HT:IDFBR blends, increasing acceptor content disrupts the polymer crystallinity, and the optimum device composition appears to be limited by polymer connectivity rather than being linked to the eutectic. The optical probes allow us to probe both the crystalline and amorphous phases, clearly revealing the compositions at which component mixing disrupts crystallinity.
|Original language||English (US)|
|Journal||Chemistry of Materials|
|State||Published - Sep 2 2020|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: E.R. is grateful to the Fonds de Recherche du Quebec-Nature et technologies (FRQNT) for a postdoctoral fellowship and acknowledges financial support from the European Cooperation in Science and Technology. J.N. acknowledges financial support from the Engineering and Physical Science Research Council (grants no EP/P005543/1, EP/R023581/1 and EP/P032591/1) and from the European Research Council for funding (grant agreement No. 742708). JN and ER thanks the Helmholtz foundation for a Helmholtz International
Fellow Award. A.A.Y.G. thanks the EPSRC for award of a postdoctoral fellowship (Grant No. EP/P00928X/1). The authors at ICMAB would like to acknowledge financial support from the Spanish Ministry of Economy, Industry and Competitiveness through the ”Severo Ocho” Program for Centers of Excellence in R&D (SEV-2015-0496) and project reference PGC2018-095411-B-I00 as well as the European Research Council (ERC) under grant agreement no.648901. I.M. acknowledges funding from KAUST, as well as EPSRC Project EP/G037515/1, EP/M005143/1, ECFP7 Project SC2 (610115), EP/N509486/1, for the financial support.