Effects of Side Chain on High Temperature Operation Stability of Conjugated Polymers

Understanding high-temperature operation in organic semiconductors remains elusive. Here, we studied the effect of two alkyl side-chains, 2-octyldodecyl (C1) and 4-decyltetracecyl (C3), on the thermal stability of two types of conjugated polymer backbones: isoindigo (IID) and diketopyrolopyrrole (DPP). All polymers remain functional with high on/off ratio in ambient air at temperature up to 220 degrees C. However, the use of longer side-chain C3 lowers the pi-pi stacking distance and enables more thermally stable polymer thin film field-effect-transistors. Specifically, IID-C3 and DPP-C3 exhibited less alteration in threshold voltage as well as a reduction in effective mobility at high temperature. This behavior emphasizes the importance of close pi-pi stacking distance on charge transport properties of conjugated polymers and their thermal stability. This study is a starting point to deconvolute the intricate mechanism of charge transport in polymer thin films at elevated temperatures.