Frequency-dependent photothermal measurement of thermal diffusivity for opaque and non-opaque materials; Application to crystals of TIPS-pentacene

TL;DR

This paper introduces a frequency-dependent photothermal method to measure the thermal diffusivity of small, opaque, and semi-opaque materials, demonstrating its application to TIPS-pentacene crystals and improving accuracy over previous techniques.

Contribution

It extends photothermal measurement techniques to materials with finite absorption, providing more accurate diffusivity values for TIPS-pentacene crystals.

Findings

Measured diffusivity of TIPS-pentacene as 0.10 mm²/s

Extended method to semi-opaque materials with finite absorption

Discussed effects of sample coating on optical properties

Abstract

We propose the use of a frequency-dependent photothermal measurement as a complement to light-flash, i.e. time-dependent, measurements to determine the through-plane thermal diffusivity of small, thin samples, e.g. semiconducting polymers and small organic molecule crystals. The analysis is extended from its previous use with some opaque conducting polymers to materials with finite absorption coefficients, such as crystals of 6,13-bis(triisopropylsilylethynyl pentacene ("TIPS-pentacene"). Taking into account the finite absorption coefficients of the latter gives a value of diffusivity, D=0.10 mm2/s, much smaller than previously estimated and more consistent with its expected value. We also briefly discuss the effects of coating samples for the measurement to improve their optical properties.