Non-Homogeneity of Distribution of Transport and Trapping States in Poly[2-methoxy-5-(3′,7′- dimethyloctyloxy)-1,4-phenylenevinylene

Abstract

Carrier transport and trapping was investigated in poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) layers by thermally stimulated currents (TSC) depending on the exciting light spectral range. The upper edge of the spectra ranged from 1.77 eV up to 3.1 eV to assure selective excitation of the defect states. The TSC curves were shown to be a superposition of several thermally activated processes, i.e., carrier generation from trapping states and thermally stimulated mobility growth according to the Gaussian disorder model. The extrinsic excitation resulted in 0.15 eV photoconductivity effective activation energy values, which decreased down to 0.05 eV for the intrinsic excitation. The deeper states with activation energies of 0.28-0.3 eV and 0.8-0.85 eV were identified too. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.