Fine-Tuning the Energy Levels of a Nonfullerene
Small-Molecule Acceptor to Achieve a High Short-Circuit Current and a Power
Conversion Efficiency over 12% in Organic Solar Cells
Kan, B (Kan, Bin)[ 1,2,3 ] ; Zhang, JB (Zhang, Jiangbin)[ 4,5 ] ; Liu, F (Liu, Feng)[ 6 ] ; Wan, XJ (Wan, Xiangjian)[ 1,2,3 ] ; Li, CX (Li, Chenxi)[ 1,2,3 ] ; Ke, X (Ke, Xin)[ 1,2,3 ] ; Wang, YC (Wang, Yunchuang)[ 1,2,3 ] ; Feng, HR (Feng, Huanran)[ 1,2,3 ] ; Zhang, YM (Zhang, Yamin)[ 1,2,3 ] ; Long, GK (Long, Guankui)[ 1,2,3 ] ; Friend, RH (Friend, Richard H.)[ 5 ] ; Bakulin, AA (Bakulin, Artem A.)[ 4 ] ; Chen, YS (Chen, Yongsheng)[ 1,2,3 ]
ADVANCED
MATERIALS, 2018, 30(3): 文献号: 1704904
DOI: 10.1002/adma.201704904
WOS:000429097600026
Abstract
Organic
solar cell optimization requires careful balancing of current-voltage output of
the materials system. Here, such optimization using ultrafast spectroscopy as a
tool to optimize the material bandgap without altering ultrafast photophysics
is reported. A new acceptor-donor-acceptor (A-D-A)-type small-molecule acceptor
NCBDT is designed by modification of the D and A units of NFBDT. Compared to
NFBDT, NCBDT exhibits upshifted highest occupied molecular orbital (HOMO)
energy level mainly due to the additional octyl on the D unit and downshifted
lowest unoccupied molecular orbital (LUMO) energy level due to the fluorination
of A units. NCBDT has a low optical bandgap of 1.45 eV which extends the
absorption range toward nearIR region, down to approximate to 860 nm. However,
the 60 meV lowered LUMO level of NCBDT hardly changes the V-oc level, and the
elevation of the NCBDT HOMO does not have a substantial influence on the
photophysics of the materials. Thus, for both NCBDT- and NFBDT-based systems,
an unusually slow (approximate to 400 ps) but ultimately efficient charge
generation mediated by interfacial charge-pair states is observed, followed by
effective charge extraction. As a result, the PBDB-T: NCBDT devices demonstrate
an impressive power conversion efficiency over 12%-among the best for
solution-processed organic solar cells.
