Decay of space charge in conjugated polymers measured using pyroelectric current transients

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 E-t= 0.6 eV and a trap density N-t> 2 x 10(21) m(-3). In poly(2,5-pyridinediyl) both electron and hole trapping are observed, and the analysis of the decays yield E-t = 0.55 eV and N-t > 10(21) m(- 3). No deep trapping could be observed in poly(9,9-dioctylfluorene), confirming the high chemical purity of this polymer. (C) 2003 American Institute of Physics.