Photoexcitation Mechanisms and Transport Properties of Polarons and Solitons in Conjugated Polymers

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

The proposed research is focused on the carrier photogeneration mechanism as well as the carrier dynamics in conjugated polymers. These will be investigated by means of two experiments: 1. Fast transient carrier density measurements in the sub-picosecond time regime, using transient photoinduced absorption probed in the 6-10 ?m spectral region, which spans the infrared active vibrational modes that arise from carriers on the polymer backbone; 2. transient photoconductivity measurements. The former measurement will determine the dependence of the carrier quantum efficiency on photon energy and interchain coupling strength, as well as carrier recombination dynamics, while the latter one will probe the carrier dynamics. The goal of this research is to investigate some of the most fundamental questions in the field of conjugated polymers: Are solitons primary excitations? What is the nature of soliton-soliton interaction? Can one cross the insulator-metal transition at high soliton excitation densities? Is carrier generation possible in strictly one-dimensional systems (e.g. on a single polymer chain)? The proposed research involves state-of-the-art experimental techniques, and thus will provide significant educational benefit to the students and post-doctoral fellows involved in the project. %%% This research is focused on the carrier photogeneration mechanism and carrier dynamics in various conjugated polymers by means of transient carrier density as well as transient photoconductivity measurements. The goal of this research is to investigate some of the most fundamental questions in the field of conjugated polymers: Are solitons primary excitations? What is the nature of soliton-soliton interaction? Can one cross the insulator-metal transition at high soliton excitation densities? Is carrier generation possible in strictly one-dimensional systems (e.g. on a single polymer chain)? Or rather, is interchain coupling inherently required for carriers to escape geminate recombination? How are the carrier quantum efficiency, carrier recombination dynamics, and carrier transport affected by modifying the inter-chain coupling? What is the role of neutral excitons in the carrier photoexcitation process? The proposed research will provide the kind of data that should bring a closure to these core questions. Additionally, the proposed research involves state-of-the-art experimental techniques, and thus will provide significant educational benefit to the students and post-doctoral fellows in the Institute for Polymers and Organic Solids at UC Santa Barbara.