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Fluorine Tuning of Morphology, Energy Loss, and Carrier Dynamics in Perylenediimide Polymer Solar Cells
journal contribution
posted on 2019-10-18, 13:40 authored by Weigang Zhu, Joaquin M. Alzola, Thomas J. Aldrich, Kevin L. Kohlstedt, Ding Zheng, Patrick E. Hartnett, Nicholas D. Eastham, Wei Huang, Gang Wang, Ryan M. Young, George C. Schatz, Michael R. Wasielewski, Antonio Facchetti, Ferdinand S. Melkonyan, Tobin J. MarksWe investigate backbone
fluorination effects in bulk-heterojunction
(BHJ) polymer solar cells (PSCs) with the fluorine-poor PBDTT-FTTE and fluorine-rich PBDTTF-FTTE donor polymers, paired
with the perylenediimide (PDI) 3D “propeller acceptor” Ph(PDI)3. The PBDTTF-FTTE:Ph(PDI)3 devices exhibit a >50% power conversion
efficiency (PCE, up to 9.1%) increase versus PBDTT-FTTE:Ph(PDI)3. This enhancement reflects structurally
optimized phase separation due to templating effects, affording reduced
energy loss, higher electron mobility, greater free charge lifetimes
and yields, and lower bimolecular recombination, as quantified by
UPS, AFM, TEM, GIWAXS, SCLC, light intensity dependence measurements,
and fs/ns transient absorption (TA) spectroscopy. In PBDTTF-FTTE, the DFT-computed dipole orientations of the ground and excitonic
states are nearly antiparallel, explaining the longer free charge
lifetimes, minimized recombination, and lowered exciton binding energy.
The PBDTTF-FTTE:Ph(PDI)3 performance
enhancement vs that of the fluorine-poor PBDTT-FTTE:Ph(PDI)3 analogue as well as the overall PSC performance
exceeds that of the corresponding PC71BM- and ITIC-Th-based cells.
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light intensity dependence measurementsoptimized phase separationperformanceenhancementexciton binding energyAFMSCLCPC 71 BMUPSPSCcharge lifetimesPBDTT-FTTETEMfluorine-rich PBDTTF-FTTE donor polymersGIWAXSPDIrecombinationfluorine-poorPCETABHJPerylenediimide Polymer Solar Cellsbackbone fluorination effects
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