not know the exact reason of the high dark current under reverse
bias, we believe it leads to the relatively low collection
efficiency and open-circuit voltage.
We have shown that photovoltaic cells can be prepared with
a fullerene–oligophenylenevinylene conjugate. The device
efficiency is not yet optimised and further improvements could
be expected by utilisation of new fullerene derivatives with a
stronger absorption in the visible range.
This work was supported by the CNRS and by a post-doctoral
fellowship from The Netherlands Organization for Scientific
Research to L. O. We further thank L. Oswald for technical
help.
Notes and references
† Selected spectroscopic data for 1: UV–VIS lmax(CH2Cl2)/nm 254
(89 800), 363 (63 200), 386 (sh, 38 800), 430 (4700), 702 (340); 1H NMR
(CDCl3, 400 MHz) d 0.87 (t, J 5.5, 6H), 1.26–1.31 (m, 36H), 1.78 (m, 4H),
2.83 (s, 3H), 3.96 (t, J 5, 4H), 4.25 (d, J 9.5, 1H), 4.94 (s, 1H), 5.00 (d, J 9.5,
1H), 6.38 (t, J 1.5, 1H), 6.65 (d, J 1.5, 2H), 7.04 (AB, J 17, 2H), 7.12 (AB,
J 17, 2H), 7.48 (s, 4H), 7.61 (d, J 8, 2H), 7.82 (br, 2H); 13C NMR (CDCl3,
100 MHz) d 14.15, 22.71, 26.11, 29.34, 29.44, 29.63, 29.66, 29.69, 31.93,
40.05, 68.10, 69.06, 70.00, 83.35, 101.03, 105.17, 126.85, 126.90, 128.12,
128.54, 128.71, 128.86, 129.68, 135.77, 135.89, 136.43, 136.55, 136.60,
136.71, 136.82, 137.44, 139.15, 139.56, 139.89, 140.14, 141.52, 141.67,
141.84, 141.91, 141.95, 142.02, 142.05, 142.10, 142.15, 142.23, 142.27.
142.54, 142.66, 142.98, 143.13, 144.37, 144.58, 144.69, 145.14, 145.28,
145.52, 145.74, 145.92, 146.05, 146.10, 146.17, 146.27, 146.30, 146.46,
146.71, 147.28, 153.37, 153.98, 156.20, 160.50; FAB-MS: m/z 1426.8
(MH+). Anal calc. for C109H71O2N: C 91.76, H 5.02, N 0.98; found: C
91.27, H 5.09, N 1.07%.
Fig. 1 Top: structure of the photovoltaic cell. Bottom: current–voltage
characteristics of the ITO/C60–oligophenylenevinylene/Al device in the
dark (2) and under 5 mW cm22 illumination (400 nm) (5).
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Benzaldimine 8 was subjected to the Siegrist reaction6 with
stilbene 4 to give protected trimer 9 in 74% yield. Treatment of
9 with CF3CO2H in CH2Cl2–H2O (1:1) afforded aldehyde 10 in
96% yield. The functionalisation of C60 was based on the
1,3-dipolar cycloaddition7 of the azomethine ylide generated in
situ from 10. The reaction of C60 with 10 in the presence of an
excess of N-methylglycine (sarcosine) in refluxing toluene
afforded fulleropyrrolidine 1 in 43% yield (or 62% based on the
non-recovered C60). All of the spectroscopic studies and
elemental analysis results were consistent with the proposed
molecular structures.† The UV–VIS spectrum of 1 corresponds
to the sum of the spectra of its two components and shows the
characteristic absorptions of a fulleropyrrolidine derivative at
254, 430 and 702 nm as well as the diagnostic oligophenylene-
vinylene band at 363 nm indicating that there are no significant
interactions between the two chromophores in the ground state.
2 N. S. Sariciftci, L. Smilowitz, A. J. Heeger and F. Wudl, Science, 1992,
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Preliminary luminescence measurements show
a strong
quenching of the oligophenylenevinylene fluorescence in 1.
Charge transfer is expected to occur and compound 1 appears as
a potential candidate for the preparation of a photovoltaic cell.
The device structure is schematically depicted in Fig. 1. The
C60-oligophenylenevinylene films were spin cast, on a glass
substrate coated with indium–tin oxide (ITO), from a 4 wt%
chloroform solution. The Al electrode was vacuum evaporated
on the films to a thickness of 100 nm. Typical current–voltage
curves (using ITO as positively and Al as negatively biased
electrodes) measured under dark and under light (400 nm, 5
mW cm22) are presented in Fig. 1. Under the light the device
shows clear photovoltaic behaviour with an open-circuit voltage
of ca. 0.2 V and a short-circuit current density of 10 mA cm22
corresponding to a collecting efficiency of 1%. Although we do
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therein.
Communication 9/00829B
618
Chem. Commun., 1999, 617–618