Morphology Regulation by Upside-Down Thermal Annealing Based on Blend Thick-Film Organic Solar Cells

The morphology property of the active layer which is determined by the post-treatment plays a critical role in optimizing the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, we present a novel upside-down thermal annealing (DTA) method to regulate the morphology of PffBT4T-2OD:PC71BM (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)]:6,6-phenyl C71 butyric acid methyl ester) and further increase the PCE. Compared with regular thermal annealing treatment, a dramatic 15% enhancement in PCE to 10.4% was obtained after the DTA process, which is attributed to the more orderly packed π–π stacking of the PffBT4T-2OD network and the redistribution of the PC71BM molecules. Besides, the DTA method is beneficial for boosting the dissociation of excitons and transport of charge carriers. This ideal bulk-heterojunction (BHJ) morphology regulation by DTA based on thick-film OSCs is an effective way to achieve high-performance OSCs.