Photo-response of the conductivity in functionalized pentacene compounds

TL;DR

This study investigates how functionalized pentacene organic semiconductors respond to light, revealing that their conductivity changes are mainly due to localized heating effects rather than direct electronic excitation.

Contribution

It introduces a new temperature-dependent photo-response method to distinguish heating effects from carrier activation in organic semiconductors.

Findings

Photo-response is mainly due to localized heating.

Wavelength studies show resonance related to electronic structure.

Conductivity is sensitive to ambient light changes.

Abstract

We report the first investigation of the photo-response of the conductivity of a new class of organic semiconductors based on functionalized pentacene. These materials form high quality single crystals that exhibit a thermally activated resistivity. Unlike pure pentacene, the functionalized derivatives are readily soluble in acetone, and can be evaporated or spin-cast as thin films for potential device applications. The electrical conductivity of the single crystal materials is noticeably sensitive to ambient light changes. The purpose, therefore, of the present study, is to determine the nature of the photo-response in terms of carrier activation vs. heating effects, and also to measure the dependence of the photo-response on photon energy. We describe a new method, involving the temperature dependent photo-response, which allows an unambiguous identification of the signature of heating effects in materials with a thermally activated conductivity. We find strong evidence that the photo-response in the materials investigated is predominantly a highly localized heating mechanism. Wavelength dependent studies of the photo-response reveal resonant features and cut-offs that indicate the photon energy absorption is related to the electronic structure of the material.