Isothermal crystallisation study of P3HT:PCBM blends as used in bulk heterojunction solar cells based on fast scanning calorimetry techniques

Post-production annealing is an important step in the preparation of bulk heterojunction solar cells, improving the efficiency. It is important to define appropriate annealing temperatures and times, therefore the isothermal crystallisation of a poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61 - butyric acid methyl ester (PCBM) blend is investigated in this study in order to better understand the annealing process. In order to achieve this, fast scanning calorimetry techniques are required that allow for high cooling rates, avoiding crystallisation during cooling and achieving a glassy blend. It is then possible to study isothermal crystallisation closer to the glass transition temperature (Tg) than by conventional DSC techniques.