Thermally Stimulated Carrier Transport in Polymers and Oxygen Related Traps in MEH-PPV Diodes
Thermally stimulated carrier transport and capture were investigated in poly [2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEHPPV) diodes. After the white light excitation we observed thermally stimulated current peaks in the regions 214–244 K and 304–394 K. They were superimposed on the thermally activated mobility growth according to the Poole-Frenkel or Gaussian disorder models. The peaks could be attributed to the carrier generation from the oxygen-related traps with activation energies 0.45–0.55 eV, 0.76–0.8 eV, and 0.76–0.9 eV. In contrast the traps could not be recharged by electric field, which resulted in a sample polarization instead. The non-exponential depolarization lasted for several thousands seconds and was not thermally activated even above the glass transition temperature, pointing out to different physico-chemical mechanisms, e.g., reversible chemical reactions or chain structure reorganization.