Thin-Film Thermal-Conductivity Measurement on Semi-Conducting Polymer Material Using the 3ω Technique

Organic solar cells have gained increasing interest in recent years due to their promising low-cost processing possibility and high throughput compared to inorganic solar cells. Since the efficiency of organic solar cells is still low, further optimization has to be done. Reliable simulation of solar cell layout and performance strongly depends on correct input data of the electrical and thermal transport properties of the applied film materials. In many cases these material properties are only available for bulk material if available at all. Owing to the given film thicknesses on the order of tenths to hundreds of nanometer and to the preparation methods, the properties of the used system can differ from the bulk material values. For determination of the thin-film thermal conductivity, only a few measurement methods are known to provide accurate results with one of them being the 3ω technique. It allows the determination of the thermal conductivity of bulk materials as well as thin films down to a thickness of around 50 nm. This study is part of an investigation on the influence of local hot spots, generated by defects in the active layer of organic solar cells, and on the charge carrier mobility as well as the propagation of the hot spot due to the thermal conduction of the material. Applying the 3ω technique, the effective thermal conductivity of solution-derived poly(3-hexylthiophene) thin films of different thickness on a common glass substrate was investigated.