Isothermal Crystallization of PC61BM in Thin Layers Far below the Glass Transition Temperature

Fast scanning chip calorimetry results on 1.25 μm thin layers of PC61BM. Evolution of the PC61BM endothermic peak during heating at 30 000 K·s−1, formed by isothermal treatments at 117 °C, over 80 K below Tg, using pathway from the molten state. An initial relaxation peak around Tg is formed which then disappears as a melting peak around 300 °C starts to form. Using fast scanning chip calorimetry it was shown that PC61BM, a widespread electron acceptor for organic photovoltaics, can crystallize when isothermally treated up to 100 K below the glass transition. At such temperatures, a two-step process seems to take place, where the amorphous phase first undergoes relaxation (i.e. densification) and then crystallizes.