Proceedings Article | 26 August 2008
Proc. SPIE. 7052, Organic Photovoltaics IX
KEYWORDS: Solar energy, Organic photovoltaics, Solar cells, Molecules, Crystals, Composites, Silicon, Coating, Fullerenes, Heterojunctions
We have fabricated organic photovoltaic cell using tetrabenzoporhyrin (BP) as a donor material. Tetrabenzoporhyrin is
formed by thermal conversion of the soluble precursor that has four bicyclo rings. Upon heat treatment above 150°C, the
precursor molecule is converted to semiconductive tetrabenzoporphyrin, which is insoluble against conventional organic
solvents. Taking advantage of this insoluble character of BP, p-i-n bulk heterojunction photovoltaic cell is successfully
fabricated from solution, with BP/BP:fullerene/fullerene trilayer, where p-layer is crystal BP, i-layer consists of both BP
and fullerene, and fullerene acts as n-layer. We have reported the
p-i-n photovoltaic cell using [6,6]-phenyl-C61-butyric
acid n-butyl ester (PCBNB) as an acceptor. This solution-processed
p-i-n device has achieved power conversion
efficiency as high as 3.4% (Jsc=9.8mA/cm2; Voc=0.62V; FF=0.56). The performance of BP device with p-i-n junction is
further improved by introducing a new fullerene for the i- and
n-layers. Taking into consideration LUMO level,
solubility and thermal properties, a novel fullerene derivative,
1,4-bis(dimethylphenylsilylmethyl)[60]fullerene (SIMEF),
is designed and synthesized. This new di-adduct fullerene , SIMEF, improves power conversion efficiency up to 4.1%
(Jsc=9.1mA/cm2; Voc=0.76V; FF=0.59). This improvement is largely due to an increased Voc. We have analyzed
BP:fullerene composite films to find that formation of meta-stable phase of BP is fully suppressed by SIMEF. Depth
profile of this p-i-n cell is measured by means of TOF-SIMS method to observe the expected vertical distribution of the
donor and acceptor that has been designed.
