Metastable polaron supporting phase in poly-p-phenylene films induced by UV illumination

TL;DR

This study uncovers a reversible, metastable phase in poly-p-phenylene films induced by UV light, which significantly enhances polaron lifetime, revealing new insights into defect-related charge dynamics in conjugated polymers.

Contribution

It reports the discovery of a UV-induced metastable phase in poly-p-phenylene films that supports long-lived polarons, a phenomenon not previously observed in this material.

Findings

UV illumination induces a reversible metastable phase with long-lived polarons.

The phase transition occurs within hours of UV exposure and reverts in half an hour in darkness.

A defect-based mechanism explains the increased polaron lifetime in the metastable phase.

Abstract

We discovered a new metastable polaron-supporting phase in pristine films of a soluble derivative of poly-p-phenylene vinylene (MEH-PPV) that is induced by UV illumination. In the initial un-illuminated phase A, the films do not show long-lived photogenerated polarons. However, prolonged UV illumination for several hours induces a reversible, me-tastable phase B that shows abundant long-lived photogenerated polarons. Phase B films transform back to the original phase A within 1/2 hour in the dark at room temperature. We propose a reversible mechanism in which UV illumination creates metastable deep defects that substantially increase the photogenerated polaron lifetime.