Mechanism of carrier generation in poly(phenylene vinylene): Transient photoconductivity and photoluminescence at high electric fields.

Abstract

The carrier generation mechanism in poly(phenylene vinylene), is addressed by studying the transient photoconductivity and the photoluminescence as a function of the external electric field E in samples oriented by tensile drawing. The transient photocurrent is proportional to E at low fields, but increases nonlinearly for Eg${10}^{5}$ V/cm. The field at which the photoconductivity becomes nonlinear (the onset field, ${\mathit{E}}_{0}^{\mathrm{pc}}$) depends on the degree of alignment: the higher the draw ratio, the lower ${\mathit{E}}_{0}^{\mathrm{pc}}$. The dependence of the photocurrent on E is similar to the dependence of the dark current on E; both imply a field-dependent mobility (rather than field-dependent carrier generation). The onset field for the nonlinear photoconductivity is, however, different from the onset field for quenching the luminescence (${\mathit{E}}_{0}^{\mathrm{pl}}$). Thus, contrary to expectations for strongly bound neutral excitons as the elementary excitations, the high-field increase in photocurrent and the corresponding decrease in photoluminescence are not proportional, indicating that field-induced carrier generation is not significant. \textcopyright{} 1996 The American Physical Society.