Effect of crystal density on sublimation properties of molecular organic semiconductors

Thermal evaporation is an essential process employed in the fabrication of optoelectronic devices based on small molecular organic materials. Knowing the evaporation properties (e.g. sublimation enthalpy, vapor pressure) of archetypal compounds and being able to predict these properties of new compounds is therefore important for the design of processes and deposition apparatus. To address this lack of reliable, easily reproducible information we used thermogravimetry to characterize the sublimation properties of pentacene; tris(8-hydroxyquinolino) aluminum (Alq3); 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA); metal-free phthalocyanine (H2Pc); boron subphthalocyanine chloride (SubPc); iron phthalocyanine (FePc); copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc). A linear relationship was found between enthalpy and vapor pressure, and crystal density, allowing for the estimation of thermophysical properties of untested compounds of a similar class using a simple model.

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► Density and sublimation enthalpy of molecular semiconductors are linearly related.
► Predictive nature of the relation is validated with known organic materials.
► Sublimation enthalpies and vapor pressures are measured using thermogravimetry.