The fast photoinduced charge transfer between conjugated polymers and the molecule C60 gives efficient charge separation and may be used when building materials suitable for photodiodes. The low cost processing techniques compatible with such materials is a strong attraction for photovoltaic devices. We report photovoltaic devices constructed using novel polythiophenes in combination with C60 molecules in form of blends and/or bilayers, which give promising results. The devices investigated were prepared in sandwich structure where the active thin layer is found between two electrodes of ITO (Indium Tin Oxide) as hole collector electrode, and aluminium as electron collector electrode. Blending two polythiophenes PTOPT (poly (3-(4-octylphenyl) 2,2-bithiophene and POMeOPT (poly(3-(2-methoxy-5-octylphenyl) thiophene) with C60 in the ratio 1:1:2 respectively, is possible to obtain very good quality spin coated films with no marked phase separation down to the range 50nm. These devices presented good performance with incident photon to electron efficiencies around 15%, under 1.5 mW/cm² of illumination at 500nm at zero applied bias.
In bilayer devices another polythiophene was used (Wm 47 (poly(3-(4-(2-(2-methoxyethoxy)ethoxy)phenyl)thiophene))) which was spin coated on the Ito/glass substrate; after that C60 was evaporated on top. The Wm 47 could be annealed in order to change its conformation and in this way to shift the peak of optical absorption to lower energies. In the bilayer devices we expect charge separation to occur at the polymer/C60 interface. Spectroscopic ellipsometry was performed in order to model this interface, which is found to be sharp. Optical modelling of the device is done to ascertain the distribution of excitons in the film.

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