Chemistry Reference
In-Depth Information
C
12
H
25
O
OC
12
H
25
OEt
O
56
55
O
O
Ar
57
58
Fig. 31 PCBM (55), DPM-12 (56) and other modified fullerenes used as successful acceptors for
photovoltaic devices
alkyl chains which improve dramatically the solubility of the acceptor in the blend
to reach efficiencies in the region of 3% (Fig.
31
). Although the LUMO energy level
for DPM12 is the same as that for PCBM, an increase in the
V
oc
of 100 mV for the
DPM12 over PCBM has been observed [
238
]. This is currently an important issue
for improving the design of future fullerene-based acceptors.
Other fullerene derivatives such as the dihydronaphthylfullerene benzyl alcohol
benzoic ester (57) described by Fr
ยด
chet et al. [
239
] have also shown their ability to
produce efficient PV devices (PCE up to 4.5%).
Hou and Li reported the preparation of a bis-adduct fullerene derivative 58
formed by two indene units covalently connected to the C
60
sphere [
240
]. Interest-
ingly, the presence of two aryl groups improves the visible absorption compared to
the parent PCBM, as well as its solubility (
90 mg/mL in chloroform) and the
LUMO energy level, which is 0.17 eV higher than PCBM. Photovoltaic devices
formed with P3HT as semiconducting polymer revealed PCE values of 5.44%
under illumination of AM1.5, 100 mW/cm
2
, thus surpassing PCBM which afforded
an efficiency of 3.88% under the same experimental conditions.
Although some of the fullerene derivatives prepared to date exhibit outstanding
performances in PV devices, the synthesis of new fullerene derivatives with
stronger visible and NIR absorption and higher LUMO energy levels than PCBM
is currently a challenge in organic photovoltaics.
>
6.2 Fullerenes for Molecular Wires
Donor-bridge-acceptor (DBA) systems, in which the bridge mediates the transport
of charge between the donor and the acceptor, provide good models to study the
