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The decay of space charge in conjugated polymers due to detrapping from deep traps after the turn-off of an external bias has been investigated. We present an experiment for measuring time-resolved laser intensity modulation method spectrum with a resolution of about 1 s. For this pyroelectric current transients have been recorded at different temperatures from 220 to 360 K. The data have been analyzed, assuming detrapping of charge carriers from single energy trap levels to a Gaussian distribution of transport levels to be the predominating process of the space-charge decay. In poly[2-methoxy, 5-(2’-ethyl-hexyloxy)-p-phenylene-vinylene], we find hole trapping with a trap depth of Et=0.6 eV and a trap density Nt>2×1021 m−3. In poly(2,5-pyridinediyl) both electron and hole trapping are observed, and the analysis of the decays yield Et=0.55 eV and Nt>1021 m−3. No deep trapping could be observed in poly(9,9-dioctylfluorene), confirming the high chemical purity of this polymer.

We demonstrate the pyroelectric effect in a conjugated polymer, poly(2,5-pyridinediyl) (PPY), and we use the laser intensity modulation method (LIMM) to resolve the spatial distribution of electric field and space charges inside a 5 μm Au/PPY/Au sandwich device. The pyroelectric signal shows hysteresis behavior with respect to the applied bias indicating permanent storage of injected charges. From the analysis of the LIMM spectra we conclude that application of a bias leads to the accumulation of space charges near the electrodes, while a zone of opposite space charge may establish in a distance of about 1 μm from it. The charged state retains after removing the bias and can lead to an internal electric field that is opposite to the external poling field in the bulk of the polymer film.

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