Environmental Engineering Reference
In-Depth Information
Table 2.4
Properties and devices characteristics for the BDT-based low band gap polymers
J
sc
(mA/cm
2
)
Polymer
Eg(opt)
(eV)
HOMO/LUMO
(eV/eV)
V
oc
(V)
FF
PCE (%)
Refs
PBDT
2.13
-5.16/- 2.67
N.A.
N.A.
N.A.
N.A.
[
59
]
PBDTE
2.03
-5.07/- 2.86
1.16
0.56
0.38
0.25
[
59
]
PBDTT
2.06
-5.05/- 2.69
3.78
0.75
0.56
1.60
[
59
]
PBDTT-E
1.97
-4.56/- 2.66
2.46
0.37
0.40
0.36
[
59
]
PBDTPZ
1.63
-4.78/- 3.28
1.54
0.60
0.26
0.23
[
59
]
PBDTBT
1.70
-5.10/-3.19
2.97
0.68
0.44
0.90
[
59
]
PBDTTPZ
1.05
-4.65/- 3.46
1.41
0.22
0.35
0.11
[
59
]
PBDTBSe
1.52
-4.88/- 3.33
1.05
0.55
0.32
0.18
[
59
]
PBDTTT-C
1.61
-5.12/- 3.35
14.7
0.70
0.64
6.58
[
14
]
PBDTTT-CF
1.60
-5.22/- 3.45
15.2
0.76
0.67
7.73
[
15
]
PBDTTT-EF
1.63
-5.12/- 3.13
14.5
0.74
0.69
7.4
[
60
]
PBDTTTPD
1.73
-5.40/N.A.
11.5
0.85
0.70
6.8
[
61
]
PBDTFTAZ
2.0
-5.36/- 3.05
11.8
0.79
0.73
6.81
[
62
]
PBDTDTffBT
1.70
-5.54/- 3.33
12.91
0.91
0.61
7.2
[
63
]
PBDTTT-C-T
1.58
-5.11/- 3.25
17.48
0.74
0.59
7.59
[
57
]
2.2.2 Electron Acceptors
Organic materials with appropriate properties, including conjugated polymers and
small molecular compounds, can be used as electron donor materials in OPV.
Many organic compounds exhibited potential properties as electron acceptor
material, but only a very few electron acceptor materials can be used in highly
efficient OPV devices. Fullerene and its derivatives are the most successful elec-
tron acceptor materials.
2.2.2.1 PCBM and the Likes
Fullerene C60 has well-symmetric structure and exhibits good electron mobility,
and as known, one molecule of C60 can receive four electrons. Therefore, C60 and
its derivatives can be used as electron acceptor materials. In 1992, Sariciftci et al.
first used C60 as electron acceptor and discovered the photoinduced ultrafast
electron transfer between electron donor and acceptor [
64
]. Although, C60 can be
dissolved in CB and DCB, it exhibits very limited solubility in most of the
commonly used organic solvents. In order to improve its solubility and also to
avoid severe phase separation of D/A blend, [6,6]-phenyl-C61-butyric acid methyl
ester (PC
60
BM) was applied in OPVs. In the past decade, PC
60
BM and its cor-
responding C70 derivative (PC
70
BM) has been dominantly used as acceptors in
OPVs. In comparison with PC
60
BM, PC
70
BM possesses stronger absorption in
visible range, and hence it attracted much interest recently. However, C70 is much
expensive than that of C60 due to its tedious purification process, which limits its
application. The molecular structures and the synthetic route of PC
60
BM, PC
70
BM
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