Thermal diffusivity measurements of novel electronic materials

Organic or hyrid organic-inorganic semiconductors are now finding widespread applications in organic light-emitting diodes (OLEDs) and organic photovoltaic (OPV) cells.[1-2] Because of these inspiring developments, numerous efforts have been devoted to understanding the optoelectronic properties of these materials, with particular emphasis on their photophysical and charge transport properties. Much less efforts, however, are focused on the fundamental thermal properties which are closely related to heat dissipation and management in organic-based devices. In OLEDs, electrical energies can be wasted in form of heat rather than light. In an OPV cell, solar energy is wasted as heat, too, rather than extracted charge carriers. How fast heat energy can escape out of an organic device will be determined by the thermal conductivity (or diffusivity) of the organic material. This proposal outlines a contactless photothermal technique for thermal diffusivity measurements. The technique is based on the mirage effect realized by the photothermal deflection measurement (PDM) of a probe beam. We will primarily focus on using PDM to study the thermal diffusivities of organic semiconductors because of their technological relevance and the need to build a data base for their thermal properties which are lacking far behind their optoelectronic properties. The outcome of this proposal should lead to a direct means for quantifying the thermal properties of organic semiconductors or novel electronic materials and better understanding in thermal diffusion in these materials. The thermal properties will be correlated to molecular structures, morphological changes (e.g. arising from additives), and charge carrier transport properties.