Carrier capture kinetics at electrical defects in poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) studied using charge transient spectroscopy

Abstract

We use charge transient spectroscopy to study the trap levels in the prototypical polymeric semiconductor poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Emission signature of the traps has been resolved using higher order spectroscopic analysis techniques of charge transients. The nature of the defect potential is best understood by studying capture mechanisms. Carrier capture kinetics of the dominant defects are studied using variable pulse-width filling technique to directly determine capture coefficients as a function of temperature. We demonstrate that charge redistribution occurs among the discrete traps through the process of multiple trapping and emission. Of the eight deep traps detected, the two dominant ones, christened T2 and T3, with activation energies of 0.38 and 0.49 eV are studied in detail. We go on to develop a phenomenological model representing the various activation energies in the mechanism of capture and emission. One of them involves a capture barrier of as high as 0.27 eV, indicating the occurrence of multi-phonon emission mechanism during capture. There is evidence to suggest that the dominant traps are different states of a defect from the same physical origin.