An origin of the irreproducibility of hole injection barrier from Au top-contact electrodes and its influence on device performance in top-contact organic field-effect transistors

Abstract To understand the origin of the irreproducibility of the hole injection barrier at the interface between Au top-contact electrodes and organic semiconductors, we performed a systematic study by focusing on the deposition rate of Au. As a benchmarking material system, we fabricated field-effect transistors with pentacene active layers and Au top-contact electrodes evaporated with the deposition rate from 0.5 to 10 A/s. From the contact potential differences (∆ CPDs ) between Au and pentacene measured with Kelvin-probe force microscopy, cross-sectional structures with scanning transmission electron microscopy, crystallographic structures with X-ray diffraction, and Au depth profiles with secondary ion mass spectrometry, we concluded that the variation of ∆ CPD is due to embedded Au nanoclusters in pentacene with the average diameter of 4~6 nm. These Au nanoclusters, of which depth significantly varies by the Au deposition rate, modulate the ∆ CPD and interfere with the reproducibility of hole injection barrier. As a result, gate threshold voltage and field-effect mobility also become irreproducible.