Abstract

Dissociation of photo-generated excitons into charge carriers (polarons) is the working principle of organic photovoltaic cells, whereas recombination of field-injected charge carriers into luminescent singlet excitons and nonradiative triplet excitons governs the efficiency of organic light emitting devices (OLED). In this paper, we address these processes in a single layer OLED based on para-hexaphenyl (PHP)¹ by conventional and electric field- assisted femtosecond pump/probe measurements. Due to its well defined conjugation length and its chemical structure PHP exhibits well resolved photo-induced absorption (PA) features, that can be assigned to singlet, triplet and polaron absorption. This allows to monitor the dynamics of field-induced singlet dissociation² and polaron recombination in a single layer OLED structure consisting of aluminum/PHP/lndium Tin Oxide (1TO) with 200 fs time resolution.

© 1999 Optical Society of America