Efficient non-fullerene organic solar cells employing sequentially deposited donor-acceptor layers

Zhang, JB (Zhang, Jiangbin)^[ 1,2 ] ; Kan, B (Kan, Bin)^[ 3,4 ] ; Pearson, AJ (Pearson, Andrew J.)^[ 1 ] ; Parnell, AJ (Parnell, Andrew J.)^[ 5 ] ; Cooper, JFK(Cooper, Joshaniel F. K.)^[ 6 ] ; Liu, XK (Liu, Xiao-Ke)^[ 1,7 ] ; Conaghan, PJ (Conaghan, Patrick J.)^[ 1 ] ; Hopper, TR (Hopper, Thomas R.)^[ 2 ] ; Wu, YT (Wu, Yutian)^[ 2 ] ; Wan, XJ (Wan, Xiangjian)^[ 3,4 ] ; Gao, F (Gao, Feng)^[ 7 ] ; Greenham, NC (Greenham, Neil C.)^[ 1 ] ; Bakulin, AA (Bakulin, Artem A.)^[ 2 ] ; Chen, YS (Chen, Yongsheng)^[3,4 ] ; Friend, RH (Friend, Richard H.)^[ 1 ] 

JOURNAL OF MATERIALS CHEMISTRY A, 2018, 6(37): 18225-18233

DOI: 10.1039/c8ta06860g

 WOS:000448340100039

Abstract

Non-fullerene acceptors (NFAs) have recently outperformed their fullerene counterparts in binary bulk-heterojunction (BHJ) organic solar cells (OSCs). Further development of NFA OSCs may benefit other novel OSC device structures that alter or extend the standard BHJ concept. Here, we report such a new processing route that forms a BHJ-like morphology between sequentially processed polymer donor and NFA with high power conversion efficiencies in excess of 10%. Both devices show similar charge generation and recombination behaviours, supporting formation of similar BHJ active layers. We correlate the approximate to 30 meV smaller open-circuit voltage in sq-BHJ devices to more substantial non-radiative recombination by voltage loss analysis. We also determine the exciton diffusion length of benchmark polymer PBDB-T to be 10 +/- 3 nm. Our results demonstrate high-efficiency OSC devices using sequential deposition method and provide new opportunities to further improve performance of state-of-the-art OSCs.