Low-Temperature Thermal Conductivity
of Rubrene Single Crystals:
A Method to Estimate
Defect Density of Organic Crystals

We disclose a method of quantitatively characterizing crystalline defects by measuring low-temperature thermal conductivity in relatively clean organic molecular crystals, which is gaining increasing interest due to recent industrial attentions to organic semiconductor crystals and nonlinear-optical crystals. As the result of the measurement with representative organic semiconductor crystals of rubrene, the “phonon peak” of the conductivity in the temperature range of 10 ~ 20 K is indeed sensitive to the amount of strain dislocations in the crystals around only 1015 cm−3, demonstrating the usefulness of the present method.

(by Y. Okada & J. Takeya)

	Fig. 1. Temperature dependence of thermal conductivity of rubrene crystals grown by three different conditions (red: from gas phase, blue: from aniline solution, and green: from p-xylene solution).
	Fig. 2. Low temperature heat capacity of a rubrene crystal.		Fig. 3. T2 vs κ plot for the rubrene crystals grown from gas phase and from aniline solution.