Shallow and deep traps in conjugated polymers of high intrachain order

Abstract

We present measurements of thermally stimulated currents and photoinduced absorption (PIA) in a planarized form of poly(para-phenylene). Due to the high intrachain order of the samples and their narrow distribution of effective conjugation lengths the density of states shows a very steep onset at the band gap energy. This is the prerequisite for detecting distinct trap levels and to determine their concentration and depth. We show that charges trapped at depths of 0.1 and 0.4 eV govern the observed charge transport and change in the absorption upon photoexcitation and in particular that the temperature dependence of the PIA intensity in the millisecond range reflects thermal effects on transport processes. © 1996 The American Physical Society.