Aggregation Tuning with Heavily Fluorinated Donor Polymer for Efficient Organic Solar Cells
Kang Xiao, Xiaoming Li, Haining Liu, Zezhou Liang, Weichao Chen, Nan Zheng, Shanlin Qiao, Renqiang Yang
Abstract
The fluorination/sulfofication-induced effect in the photovoltaic polymer solar cells (PSCs) needs to be paid much attention. In this work, a new donor polymer PBDB-PS2F was synthesized by heavily fluorinated and decorated S atom on the side chain of benzo[1,2-b:4,5-b′]dithiophene (BDT) unit to explore the internal combined effect of F&S on the photoelectric performance. It was found that the heavy fluorination on the side chain could make PBDB-PS2F achieve a low highest occupied molecule orbital (HOMO) energy level of −5.72 eV and weaken the torsion of the main chain and effectively increase the intermolecular π–π* transition. Encouragingly, compared with the counterpart polymer PBDB-PS without the fluorination, PBDB-PS2F exhibited a much intense aggregation at room temperature but showed a tendency of reduced aggregation at high temperatures. This feature gives excellent solution processability and uniform morphology in the active layer of a PBDB-PS2F-based device, enabling an outstanding photovoltaic performance with the power conversion efficiency (PCE) of 13.56% (VOC = 0.90 V, JSC = 21.53 mA/cm2, FF = 69.68%). Compared with that of the counterpart polymer PBDB-PS with no heavy fluorination, the VOC of PBDB-PS2F increased by 15.4% and the PCE increased by 30.9%. Thus, the heavy-fluorination-induced effect to construct photovoltaic polymers could be used to improve the performance of polymer solar cells.