International audienceThe energy conversion efficiency of organic solar cells based on simple electron donor/electron acceptor heterojunction has been studied as a function of the interface anode/electron donor. The anode is fluorine doped tin oxide film. It is shown that the solar cell efficiency increases when a metal ultra thin layer is introduced between the anode and the electron donor. Experimental and theoretical studies show that the work function value of the metal is one of the main factors which allow improving the organic solar cells performances, via better hole collection efficiency
Due to their light weight, flexibility and semi-transparency the organic photovoltaic cells play an important role for solar conversion photovoltaic (OPV). To achieve good performances, both donor and acceptor materials in OPVs need to have good extinction coefficients, high stabilities and good film morphologies. Since the donor plays a critical role as the absorber to solar photon flux, donor materials require wide optical absorption to match the solar spectrum. In this work the couple ED/EA in planar heterojunction was Tetracyano 4,4'-bis(9Hcarbazol-9-yl) biphenyl (TCC)/fullerene (C60). Optimum results are obtained when MoO3 alone is used as Hole Transporting Layer (HTL). The J/V characteristics do not exhibit S-shaped curves up to a TCC layer thickness of 15 nm, while they did when the HTL includes CuI. Theoretical study, complementary to the experimental study, shows that in the case of S-shaped curve the cell behaves as if it was made up of 2 diodes, one of which would be opposed to the flow of the photogenerated current. In the case of MoO3 HTL, i.e; without shaped curve, the optimum thickness is 13 nm, giving an efficiency η = 2.30% with V
oc = 0.9 V, J
sc = 5.17 mA/cm2 and FF = 49%.
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