Effects of polymer matrix on the transient Photo-EMF from organic dye pigment layers

The influence of the polymer matrix on the parameters of the transient Phot o-Electro Motive Force (PEMF) was investigated using Copper(II)-phthalocyan ine (CuPc) and N,N'-Dimethylperylene-tetracarboxylic-bismide (MePe) as pigm ents in solid pigment-polymer dispersion layers. 13 polymers with dielectri c constants epsilon (r) in the range of 2,5 - 50 were used. The maximum voltage U-MAX Of the PEMF decreases with increasing dielectric constant epsilon (r) as it is expected from the coulomb law. Unexpectedly t here is only a trend in U-MAX as a function of 1/epsilon (r), indicating ad ditional influence of the matrix. Sign (+/-) and decay behaviour U=f(t) wil l be not influenced by matrix effects. Action spectra U-MAX=f(lambda (EXC)) of MePe/Polymer dispersion layers (polyvinyl butyral, polystyrene, polyvin yl chloride, cellulose-dinitrate) do show a change in sign of PEMF at lambd a (EXC) = 600-605 nm independently on the kind of polymer. Using pure matri x-free MePe polycrystalline layers (tablets) this change in sign is shifted to lambda (EXC) greater than or equal to 615nm. Additionally, at lambda (E XC) greater than or equal to 615nm U-MAX is very small and the decay U=f(t) is accelerated That can be attributed to a fast charge transport between t he microcrystallites in the tablet due to the mutual contact of the MePe-pa rticles.