High Crystallininty Regioregular Polymer Donor by Thermal Annealing for Thickness-Insensitive Organic Photovoltaics
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To successfully develop a regioregular polymer (PDBD-FBT), a symmetric monomer synthesized in high yield by tin homo-coupling reactions. PDBD-FBT is suitable as a donor material in OPVs because it shows high crystallinity and strong face-on packing properties. These properties were amplified by thermal annealing (TA) treatment. Using PDBD-FBT as a polymer donor and Y6-HU as an electron acceptor, a PCE of 7.91% was achieved without any treatment at an optimized active layer film thickness. After TA treatment, a PCE of 12.53% was achieved with a 58% increase compared with the reference devices. Owing to the strong crystallinities, trap-assisted recombination occurs by excessively formed grain boundaries; however, efficient exciton dissociation sufficiently covers these drawbacks. Even in the thick film of the active layer, this tendency is more pronounced.