Benzo1,2-b:4,5-b′Difuran-Based Polymer for Organic Solar Cells with 17.5 Efficiency via Halogenation-Mediated Aggregation Control

摘要

The realization of high-efficiency organic solar cells (OSCs) from renewablesources will bring a real green energy technology. Benzo[1,2-b:4,5-b′]difuran(BDF) is such a building block for photovoltaic polymers as it can be builtfrom furfural, which is available from trees and vegetables. However, thedevice performance of BDF-based polymers is limited by aggregation propertiesand unfavorable active layer morphology. Herein, two new BDF-basedwide bandgap-conjugated polymers, PFCT-2F and PFCT-2Cl, are developed bycopolymerizing the fluorinated or chlorinated BDF units with the 3-cyanothiopheneunit for use as electron donors in OSCs. Benefitting from the morerotatable nature of the side-chain thiophene rings on the BDF unit, PFCT-2Clexhibits more adjustable aggregation, higher π–π stacking ordering, andappropriate miscibility with the electron acceptor. As a result, a high powerconversion efficiency (PCE) of 17.2% is offered by PFCT-2Cl, which is nearlytwo times higher than that of PFCT-2F (8.9%). A more remarkable PCE upto 17.5% is further achieved by PFCT-2Cl in a ternary OSC, which is the newefficiency record for BDF-based polymers. This success proves the criticalrole of aggregation control in BDF-based polymers and the bright future forconstructing high-performance OSCs from bio-renewable sources.