Regulating the vertical phase distribution by fullerene-derivative in high performance ternary organic solar cells

• Published in: Nano energy Vol. 46; pp. 81 - 90
• Main Authors: Bi, Pengqing, Xiao, Tong, Yang, Xiaoyu, Niu, Mengsi, Wen, Zhenchuan, Zhang, Kangning, Qin, Wei, So, Shu Kong, Lu, Guanghao, Hao, Xiaotao, Liu, Hong
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2018
• Subjects: Charge transport; Non-fullerene acceptor; Ternary organic solar cells; Vertical phase distribution; Vertical phase distribution; Ternary organic solar cells; Charge transport; Non-fullerene acceptor
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2018.01.040

The vertical phase distribution of components in bulk heterojunction is diversified in organic solar cells (OSCs). The electron donors (acceptors) can be accumulated (depleted) at the interface of active layer and charge extraction layer. The variation of vertical phase distribution significantly influences device performance because of its impact on the charge transport and charge recombination. In order to achieve favorable vertical phase distribution in OSCs based on poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-co-(1,3-di(5-thiophene-2-yl)–5,7-bis(2-ethylhexyl) benzo[1,2-c:4,5-c′]dithiophene-4,8-dione)] (PBDB-T):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))−5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC), phenyl-C71-butyric-acid-methyl ester (PC71BM) was incorporated into the binary system to fabricate ternary OSCs. In the ternary blend, PC71BM can effectively regulate the phase distribution of PBDB-T and ITIC in vertical direction, which provides favorable vertical phase distribution for charge transport. Moreover, the addition of PC71BM can also effectively increase the π-π stacking coherence length of both donor and acceptor, which facilitates charge transport and reduces the bimolecular recombination. The addition of an appropriate quantity of PC71BM can obviously improve both fill factor and short-circuit current density of the OSC based on PBDB-T:ITIC while open-circuit voltage reduces only about 0.01 V, which indicates a rational low energy loss. Consequently, the ternary OSC exhibits a best PCE of 11.0% compared to the 9.6% PCE of the binary counterpart. Ternary system of PBDB-T:PC71BM:ITIC is systematically investigated by depth-resolved light absorption spectroscopy, GIWAXS, and transient absorption spectroscopy. It is proved that PC71BM can regulate the phase distribution of PBDB-T and ITIC in vertical direction. As a result, the ternary OSC exhibits a best PCE of 11.0% compared to the 9.6% PCE of the binary counterpart. [Display omitted] •PC71BM in the ternary blends can effectively regulate the vertical phase distribution of PBDB-T and ITIC.•π-π stacking coherence length of both PBDB-T and ITIC in ternary blends were increased by the PC71BM.•Efficient charge transport, charge collection and reduced the bimolecular recombination were achieved in the ternary blends.•The PCE of binary OSC was obviously improved by the additional PC71BM from 9.6% to 11.0%.