Thermal conductivity of organic semiconducting polymers: localization, rule of mixtures, and “hyper-insulting” PCBM

In our recent paper published in Applied Physics Letters (Applied Physics Letters 102, 251912 (2013)), we measure the thermal conductivities of a range of organic semiconducting polymers common in photovoltaic devices.  We report on the thermal conductivity of PEDOT:PSS, P3HT, PCBM, and mixtures of P3HT and PCBM.  Thermal conductivities vary from 0.031±0.005 to 0.227 ± 0.014  W m⁻¹ K⁻¹ near room temperature and exhibit minimal temperature dependence across the range from 319 to 396 K. The thermal conductivities of P3HT/PCBM blend films follow a rule of mixtures, and no percolation threshold is found. We also find that thermal annealing of blend films has a variable effect on thermal conductivity.  Finally, we measure variations of thin film PCBM spun under different processing conditions, and show that even when accounting for large uncertainties in heat capacity (which we discuss in the supporting information of this article), PCBM still exhibits exceptionally low, “hyper-insulating” thermal conductivities, varying from 0.031 – 0.057 W/m/K.

This work was a collaborative effort with Dr. Mool Gupta in the ECE Department at U.Va.  This work was partially supported by the Army Research Office (Program Manager: Pani Varanasi).