The performance improvement in pentacene organic thin film transistors by inserting C60/MoO3 ultrathin layers

A series of bottom-gated top-contact pentacene organic thin film transistors are fabricated. C60 and/or MoO3 ultrathin layers are inserted between the pentacene and Al source-drain electrodes to reduce the contact resistance. With proper order and thickness of the two layers modification, the injection barrier is greatly lowered down and the field-effect mobility increases from 0.095 cm2/(V s) to 0.65 cm2/(V s). The threshold voltage decreases from −11.3 V to −6.4 V. It means that the injection barrier plays an important role in the contact resistance without modification and multiple ultrathin layers modification is an effective method to improve the performance of the OTFTs. Then the output curve of the devices with better modification is simulated by a charge drift model. Taking into account of the contact effect, the field-effect mobility is improved to 1.05 cm2/(V s). It indicates that after modification, the injection barrier is lowered down, but the contact resistance caused by the charge drift in the contact region become the more important role and still affect the performance.