Disubstituted perylene diimides in organic field-effect transistors: Effect of the alkyl side chains and thermal annealing on the device performance

Using a series of eight substituted perylene diimides (PDIs) we have explored the effects of the side chains and thermal annealing of the semiconductor films on their electrical characteristics in organic field-effect transistors (OFETs). Clear correlations between the thermally-induced improvement in the crystallinity of PDI films, their phase transition temperatures determined by differential scanning calorimery (DSC) measurements and the electrical characteristics of the OFETs have been revealed. It has been also demonstrated that the best charge carrier mobilities are delivered by PDIs showing the highest enthalpies of the phase transitions, manifesting particularly strong intermolecular interactions in these crystalline solids. On the other hand, the length of alkyl side chains represents a crucial parameter governing the device performance. PDIs with the linear C-6-C-8 alkyl side chains showed the highest charge-carrier mobilities when annealed in optimal regimes, which correlates well with the thermal and structural characteristics of these materials. Finally, we show that DSC can be considered as a very useful technique to speed up the discovery of new promising semiconductor materials via screening for the highest phase transition enthalpies and performing film annealing near the phase transition temperatures.