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The results on characterization of the main photoelectric properties of the polymer:fulleren based composite
material by using the non-steady-state photo-electromotive force (p-EMF) and modulated photocurrent technique are
presented. By measuring this current under different experimental conditions, important material photoelectric
parameters such as drift L0 and diffusion length LD, photocarrier's lifetime τ ; quantum efficiency of charge
generation φ can be determined. The 50% of the composite weight consists of a mixture of the hole-conducting
polymer PF6:TPD (poly-hexyle-triophene:N,N'-bis(4-methylphenyl)-N,N'-bis-(phenyl)-benzidine) sensitized with the
highly soluble C60 derivative PCBM (phenyl-C61-butyric acid methyl ester) . Seven samples with varied
polymer:sensitizer weight ratio (49:1wt.-%, 45:5wt.-%, 40:10wt.-%, 15:35wt.-%, 25:25wt.-%, 10:40wt.-%, 5:45wt.-%)
where prepared. The remaining 50% were two azo-dyes 2,5-dimethyl-(4-p-nitrophenylazo)-anisole (DMNPAA) and 3-
methoxy-(4-p-nitrophenylazo)-anisole (MNPAA) (25wt.-% each). Photoconductive composite film was sandwiched
between two glass plates covered by transparent ITO electrodes. Two counter-propagating beams derived from a cw
HeNe laser (λ = 633nm) intersected inside the detector creating an interference pattern. The output photo-EMF
current (SEE MANUSCRIPT FOR EQUATION) was detected as a voltage drop by a lock-in amplifier.
At polymer sensitizer ratio 25:25wt.-% the signal sign changes to the opposite revealing that the majority
carriers at this and higher concentration of sensitizer are electrons. Our results show that the majority carrier's lifetime
τ is only slightly affected by the variations of sensitizer concentration. Mobility-lifetime product μhτh of holes, on its
turn decreases at the increasing sensitizer concentration, while μeτe of electrons keeps increasing. All this indicates that
the carrier's mobility is strongly influenced by the changes on sensitizer concentrations.
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