Thermally stimulated currents in undoped poly(p-phenylene vinylene) and the effect of stretching

Thermally stimulated current (TSC) measurements have been performed on undoped stretched poly(p-phenylene vinylene) (PPV). Two TSC peaks P 1 and P 2 are observed and become smaller as the stretching ratio was gradually increased. The trap depths are evaluated from the initial increasing part of each separated peak by the thermal cleaning method to be about 0.36 eV and 0.55 eV for peaks P 1 and P 2 , respectively, regardless of the stretching ratio. However, the second peak P 2 is markedly suppressed on stretching. Peak P 1 is interpreted as originating from electron traps formed by impurities such as a bromine (Br 2 ) or sulphur trioxide (SO 3 ) which were not eliminated by heat treatment. In contrast peak P 2 was confirmed to be based on defects already existing in the amorphous parts of PPV since the crystallinity in PPV increases and the spin density evaluated by integration of the electron spin resonance spectra in stretched PPV decreases on increasing the stretching ratio.