Room temperature and non-halogenated solvent processed terpolymers for high-efficient polymer solar cells

Abstract

Most of polymer solar cells (PSCs) are currently processed using halogenated solvents and require high temperature manufacturing. However, the realization of non-halogenated environmental-friendly solvents processing and room temperature treatment are the basis for future commercialization of batteries. In this work, two terpolymers PffBT4T-4T2FC-9/1 and PffBT4T-4T2FC-4/1 were synthesized by introducing a self-assembly third unit, bis(2-hexyldecyl)5,5‴-dibromo-3″,4′-difluoro-[2,2’:5′,2’’:5″,2‴-quaterthiophene]-3,3‴-dicarboxylate (4T2FC) into the poly [(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di (2-octyldodecyl)-2,2’; 5′,2’’; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) polymer matrix via random copolymerization. The obtained terpolymers have relatively weaker self-aggregation properties and enable the spin-coating process at room temperature compared with the pristine copolymer PffBT4T-2OD. More importantly, the ester group of the 4T2FC unit can improve the solubility of the conjugated polymers in halogen-free solvent. Ultimately, a superior power conversion efficiency (PCE) of 9.11% was obtained from the optoelectronic device based on PffBT4T-4T2FC-9/1, which is one of the highest values of PSCs based on fullerene system treated with non-halogenated solvents at room temperature. These results demonstrate that these new terpolymers with ester group are promising candidates for high performance environmental-friendly solvent processed solar cells.