Defect states investigation in poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)

In this study, application of the charge based Deep Level Transient Spectroscopy (Q-DLTS) has been extended to poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) single layer diodes, whose cathode consisted of aluminium and anode of indium tin oxide (ITO). The results reveal a broad Q-DLTS spectrum, with at least two maxima, consistent with a complex distribution of trap states. Only the Q-DLTS maximum with the shortest relaxation time could be fully resolved over the temperature range used here (100–300 K), yielding activation energies and capture cross sections in the ranges 0.3–0.4 eV and 10− 20–10− 18 cm2, respectively. It will be shown that this energy level is likely related to a majority-carrier (hole) trap, consistent with a Poole–Frenkel injection mechanism and p-type doping of the MEH-PPV film. The origin of the second (non-resolved) Q-DLTS peak will also be discussed.