Thermal conductivity and heat capacity of poly(3-octylthiophene-2,5 diyl) and its multi-wall carbon nanotube composites
Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting polymer materials used for organic solar cells. Thermal properties data, especially the thermal conductivity of the active material of solar cells, is of fundamental importance. Such data for P3OT are barely available in the literature. The photoacoustic technique is employed to measure thermophysical properties of P3OT including thermal diffusivity, thermal effusivity, specific heat capacity and thermal conductivity. The obtained results are confirmed by many measurements as well as by using more than one method. A remarkable method for thermal effusivity measurements of surface coating as well as bulk samples is introduced. The development of P3OT thermophysical properties with multi-wall carbon nanotube (MWCNT) loading as high as 6% volume fraction is investigated. Continuous enhancement of thermal diffusivity as well as thermal effusivity of P3OT is obtained with increasing MWCNT content. By using the mixed model for the thermal conductivity of a two phase system, we are able to estimate the thermal diffusivity and the thermal effusivity of MWCNTs. A considerable enhancement in thermal conductivity of larger than twice that of neat P3OT at nanotube loading ≈6% volume fraction is obtained. Theoretical analysis of the experimental results generating an interfacial thermal resistance of MWCNTs as Rk = 5.8 × 10-8 m2K W-1.