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The influence of the cathode electrode on the characteristics of pentacene/perylene derivatives based organic solar
cells was analysed by means of absorption, photoluminescence, and
X-ray spectroscopies. We report the characteristics
of a series of organic solar cells fabricated with Al, Ag, and Au electrodes for the interface between metals and organic
semiconductors, which play a central role in the physics of organic solar cells. Donor and acceptor layers of a solar cell
were pentacene and N,N'-dioctyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-8C) and
N,N'-ditridecyl-3,4,9,10-perylene-tetracarboxylic diimide (PTCDI-13C) respectively. Two organic solar cells with
pentacene/PTCDI-8C and pentacene/PTCDI-13C heterojunctions as active layers were fabricated to compare the
influence of power conversion efficiency among perylene derivatives with various numbers of carbon molecules by
means of J-V measurements. Under the sunlight simulator with an AM1.5G filter and power of 100 mW/cm2, the solar
cells of the pentacene/PTCDI-13C heterojunction with the Ag cathode had J-V characteristics of short-circuit current density of 0.415 mA/cm2, open-circuit voltage of 0.413 V, fill factor of 0.55, and power conversion efficiency of 0.1%,
which were better than those of the pentacene/PTCDI-8C heterojunction. Moreover, according to the thin film analysis,
the PTCDI-13C thin film's excitons at the interface of the heterojunction for dissociation were more, and the probability
of radiative recombination of the electron-hole pair was less than for the PTCDI-8C. The PTCDI-13C thin-film
possessed better carrier mobility than PTCDI-8C. Therefore, we could conclude that the factors mentioned above are
keys to the pentacene/PTCDI-13C-based solar cells' better power conversion efficiency. The carrier transportation
mechanism of these solar cells is discussed clearly.
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