New electron donor in planar heterojunction: optimization of the cells efficiency through the choice of the hole-extracting layer ★

International audienceDue 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 (C 60). Optimum results are obtained when MoO 3 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 MoO 3 HTL, i.e; without shaped curve, the optimum thickness is 13 nm, giving an efficiency h = 2.30% with V oc = 0.9 V, J sc = 5.17 mA/cm 2 and FF = 49%

Effect of MoO3 in the cathode buffer layer on the behaviour of layered organic solar cells

The behaviour of small-molecule organic solar cells based on copper-phthalocyanine/fullerene with different cathode buffer layer is investigated as a function of air exposure duration. The effect of MoO3 on the properties of photovoltaic solar cells (OPVCs) when it is introduced in the cathode buffer layer (CBL), has been studied. Photovoltaic performances were measured as a function of time of air exposure. During the first days of air exposure, the efficiency of the OPVCs with MoO3 in their CBL increases significantly, while it decreases immediately after air exposure in the case of reference OPVCs, i.e. without MoO3 in the CBL. Nevertheless, the lifetime of the OPVCs with MoO3 in their CBL is around 60 days, while it is only 10 days in the case of reference OPVCs. The initial increase of the OPVC with MoO3 in their CBL is attributed to the slow decrease of the work function of MoO3 due to progressive contamination. Then, the progressive degradation of the OPVCs efficiency is due to water vapour and oxygen contamination of the organic layers. The use of double CBL, Alq3/MoO3, allows to interrupt the growth of pinholes, defects and increases the path of permeating gas. Also it can prevent the contamination of the organic layer by Al. All this results in significant increase of the lifetime of the OPVCs