Poly [2,7-(9,9-dihexylfluorene)]-block-poly[2-(dimethylamino)ethylmethacrylate] as resilient cathode interlayers in polymer solar cells: the effect of block ratios

A series of alcohol-soluble diblock copolymers PF15-b-PDMAEMA(975) are applied as cathode interlayers in the PSCs based on PTB7-Th:PC71BM. Herein, the PF units are fixed at 15, and the PDMAEMA units vary as 60, 150 and 975. The device results show that varying the length of PDMAEMA block has a little effect on the performance of the devices, and all the devices show comparable and even higher performances in comparison to the devices based on the well-known PFN-Br. Control experiment indicates that the PF unit is necessary for the high performances. The improvement of the performance should be attributed to the reduction of work function and balance of charge carrier mobilities upon addition of the cathode interlayers. We believe that this type of co-polymers should be resilient to the block ratios, and may be developed to a potential cathode interfacial material in highly efficient organic solar cells.