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Experimental data are presented showing that recombination of free carriers occurs in the bulk of mm size samples of PDA-TS single crystals under steady-state excitation. The results, combined with the shape of the photocurrent i dependence on field strength, E , lead to the following conclusions: 1) the quantum yield of free carriers cp does not depend on the field strength at E < lo3 Vlcm but increases at higher E; 2) cp depends also on the diffusion length L of free carriers before recombination in the bulk of the crystal: cp -L -l . The latter accounts for the unusual type of i dependence on I, i -1"' where rn varies with the intensity of the light I in the range 1 2 rn 2 2/3. The properties of geminate diffusive pairs of charges of opposite signs are responsible for the photogeneration of free carriers.These pairs are as large as L = cm which is much higher than Onsager's radius r,. The diffusive pairs are responsible also for the magnetic field effect on the photocurrent observed.

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Experimental data are presented which give evidence about the short free path before recombination of free charge carriers in single crystals of polydiacetylene-toluene-sulphonate (PDA TS). The free path is shown to be much shorter than the millimetre-size electrode spacing. The recombination of carriers occurs via traps (of Shockly-Read type) or, at higher intensities, bimolecularly. The results obtained do not allow the authors to consider as substantiated the literature data on high (up to 105 cm2 V-1 s-1) mobility of carriers in PDA TS, and on the validity of one-dimensional diffusive theory of charge-pair separation as applied to PDA TS. All these data critically depend on the assumption of the absence of recombination.