Table 1 Device characteristics of photovoltaic solar cells incorporating PBDTBO:PC61BM blends prepared at various weight ratios
PBDTBO/PC61BM (w/w) Thickness/nm Voc/V Jsc/mA cmꢀ2 FF (%) PCE (%) Rsh/O cm2 Rs/O cm2 Mobility/cm2 Vꢀ1 sꢀ1
1 : 1
1 : 2
1 : 3
1 : 4
144
135
122
127
0.86
0.81
0.8
10.4
9.7
8.5
7.1
64.4
57.2
59.5
57.1
5.7
4.5
4.0
3.2
8695
1960
865
8.2
10.8
17.3
15.8
1.7 ꢁ 10ꢀ4
1.1 ꢁ 10ꢀ4
7.7 ꢁ 10ꢀ5
4.9 ꢁ 10ꢀ5
0.8
680
We measured the external quantum efficiencies (EQEs) of
these devices to examine their photoresponses. The devices
were first encapsulated in a N2-filled glove box; their EQEs
were measured in air. Fig. S3 (ESIw) displays EQE spectra of
the PBDTBO/PC61BM devices prepared at various blend
weight ratios; each of them exhibited a broad response from
350 to 700 nm. The EQE curve of the optimal device, based
on the (1 : 1, w/w) PBDTBO/PC61BM blend, exhibited a
maximum intensity of 60% at 570 nm. The value of Jsc
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obtained through integration of this EQE curve (9.7 mA cmꢀ2
)
was in reasonable agreement (only 6% lower) with that measured
from the J–V curve (10.4 mA cmꢀ2).
In conclusion, we have used Stille coupling to prepare a low-
bandgap conjugated polymer, PBDTBO, featuring alternating
BDT and BO units in its backbone, that exhibited good
thermal stability, acceptable solubility, high molecular weight
(Mn = 62 kg molꢀ1), and a low HOMO energy level. A PSC
device incorporating PBDTBO and PC61BM (blend weight
ratio, 1 : 1), prepared without requiring special treatment,
exhibited a high open-circuit voltage (0.86 V) and a high solar
energy PCE (5.7%).
V. R. Donuru, H. Liu and J. M. J. Fre
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This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 8877–8879 8879