Thermal conductivity of organic semi-conducting materials using 3omega and photothermal radiometry techniques

¹ Institut des Matériaux Jean Rouxel, CNRS, University of Nantes, 2 rue de la Houssinière, 44322 Nantes Cedex 3, France
² Laboratoire de Thermocinetique, CNRS, University of Nantes, LUNAM, BP. 50609, 44306 Nantes Cedex 3, France
³ University of Reims Champagne Ardenne URCA, GRESPI, Multiscale Thermophysics Lab., Moulin de la Housse, BP. 1039, 51687 Reims, France
⁴ University of Toulouse; UPS, CNRS, INP; Laboratoire Plasma et Conversion d'Energie, Toulouse, France

Published online: 10 December 2014

Abstract

Organic semiconductors for opto-electronic devices show several defects which can be enhanced while increasing the operating temperature. Their thermal management and especially the reduction of their temperature are of great interest. For the heat transfer study, one has to measure the thermal conductivity of thin film organic materials. However the major difficulty for this measurement is the very low thickness of the films which needs the use of very specific techniques. In our work, the 3-omega and photothermal radiometric methods were used to measure the thermal conductivity of thin film organic semiconducting material (Alq3). The measurements were performed as function of the thin film thickness from 45 to 785 nm and also of its temperature from 80 to 350 K. With the 3 omega method, a thermal conductivity value of 0.066 W.m⁻¹K⁻¹ was obtained for Alq3 thin film of 200 nm at room temperature, in close agreement with the photothermal value. Both techniques appear to be complementary: the 3 omega method is easier to implement for large temperature range and small thicknesses down to a few tens of nanometers whereas the photothermal method is more suitable for thicknesses over 200nm since it provides additional information such as the thin film volumetric heat capacity.