Optimized domain size and enlarged D/A interface by tuning intermolecular interaction in all‐polymer ternary solar cells

The selection of sensitizer and its existence in the blend films are important to the performance of all‐polymer ternary solar cells. Herein, all‐polymer ternary solar cell devices, which used poly4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo1,2‐b:4,5‐b′] dithiophene‐alt‐3‐fluorothieno3,4‐b]thiophene‐2‐carboxy‐late] (PTB7‐Th) as donor, polyN,N‐bis(2‐octyldodecyl)‐napthalene‐1,4,5,8‐bis(dicarboximide)?2,6‐diyl]‐alt‐5, 5′‐(2,2′‐bithiophene)] (N2200) as acceptor and polyN?900‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(40,70‐di‐2‐thienyl‐20,10,30‐benzothiadiazole) (PCDTBT) as sensitizer, are successfully demonstrated. The intermolecular interaction between donor PTB7‐Th and sensitizer PCDTBT may lead to aggregation of PTB7‐Th which decreases domain sizes and enlarges D/A effective interface area. In addition, the PCDTBT molecules also extend light absorption and cascaded energy levels of the ternary blend system. As a result, with 15% PCDTBT we get a power conversion efficiency of 5.11%, almost 20% higher than control device due to more favored exciton dissociation and higher charge transport efficiency. This study reveals a promising way to achieve high efficiency all‐polymer solar cells using a low‐band gap polymer PCDTBT. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1811–1819