Influence of thin-film processing on the performance of organic field-effect transistors

Abstract

Due to their functional and processing versatility, organic semiconductors have gained much interest in recent years. Tailoring the charge transport in a polymeric semiconductor system is imperative for developing optimized devices. Factors such as selection of solvent species and annealing temperature play a significant role in deciding the morphology of the polymer semiconductor and hence the device performance. Bottom-gate bottom-contact organic field-effect transistors were fabricated with regioregular poly(3-hexylthiophene) (P3HT) as the active material. The effects of using chlorobenzene and o-dichlorobenzene as the solvents for P3HT and annealing temperatures on the device performance were evaluated. The devices made using chlorobenzene showed greater field-effect mobility compared to those fabricated with o-dichlorobenzene. This behavior can be attributed to the disentanglement of polymer chains in a solvent with better matching solubility parameters and subsequent ease of arranging in ordered structures during processing. Furthermore, annealing the o-dichlorobenzene devices at temperatures closer to the crystallization temperature of P3HT showed an increase in field-effect mobility. At temperatures closer to the crystallization temperature, a polymer film in a semidry state can allow increased ordering of the chains leading to enhanced charge transportation.