Enhanced Performance of Fullerene n‐Channel Field‐Effect Transistors with Titanium Sub‐Oxide Injection Layer

Enhanced performance of n‐channel organic field‐effect transistors (OFETs) is demonstrated by introducing a titanium sub‐oxide (TiO x ) injection layer. The n‐channel OFETs utilize [6,6]‐phenyl‐C 61 butyric acid methyl ester (PC 61 BM) or [6,6]‐phenyl‐C 71 butyric acid methyl ester (PC 71 BM) as the semiconductor in the channel. With the TiO x injection layer, the electron mobilities of PC 61 BM and PC 71 BM FET using Al as source/drain electrodes are comparable to those obtained from OFETs using Ca as the source/drain electrodes. Direct measurement of contact resistance ( R c ) shows significantly decreased R c values for FETs with the TiO x layer. Ultraviolet photoelectron spectroscopy (UPS) studies demonstrate that the TiO x layer reduces the electron injection barrier because of the relatively strong interfacial dipole of TiO x . In addition to functioning as an electron injection layer that eliminates the contact resistance, the TiO x layer acts as a passivation layer that prevents penetration of O 2 and H 2 O; devices with the TiO x injection layer exhibit a significant improvement in lifetime when exposed to air.