Fast scanning chip calorimetry study of P3HT/PC 61 BM submicron layers: structure formation and eutectic behaviour

Fast scanning chip calorimetry was used to perform an elaborate isothermal study of poly(3‐hexyl thiophene)/[6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (P3HT/PC 61 BM) submicron layers. The used scanning rates of 30 000 K s −1 allow for a ‘true’ isothermal study, where non‐isothermal effects are avoided. Results were obtained over a wide temperature range for the 1:1 composition, used in organic solar cells, and for selected temperatures for the 3:7 composition. The results can be clearly interpreted according to the eutectic behaviour expected for this system, with the 1:1 composition being enriched in P3HT and the 3:7 composition being enriched in PC 61 BM. In both cases, the start of the melting trajectory corresponding to the eutectic transition coincided with the T g of PC 61 BM. This is in agreement with earlier studies that report a vitrification effect caused by PC 61 BM. A bell‐shaped curve of isothermal crystallization rates could be constructed for the 1:1 composition, where the T g of the mixed amorphous phase as well as of the separate components can be seen to play a role. For the 3:7 composition, clear indications are observed that a vitrified PC 61 BM phase can be formed in which isothermal crystallization takes place. © 2018 Society of Chemical Industry