Studies On The Common Source Electrodes Of Vertical Organic Light-emitting Transistors

Organic light-emitting transistors (Organic light-emitting transistor, OLET) are new electroluminescent devices, which integrate organic light-emitting diodes (OLED) with organic thin film transistors (OTFT). OLET have two functions: emitting light and adjusting current like a transistor. Luminescence intensity can be controlled by changing the gate voltage. In an OLET device, operating voltage is reduced and the luminous efficiency is improved due to shortened channel length with a vertical configuration.In this paper, we fabricated VOLET devices with common source electrode of different materials, shapes, and thicknesses, and studied their opto-electrical characteristics.Firstly, we made a VOLET device using a single source electrode of aluminum, whose structure is ITO/Pentacene (40 nm)/Alq3 (60 nm)/Al (25 nm)/LiF (150 nm)/ Al. We found that the gate voltage didn't adjust the current well.Secondly, special masks were made for changing the morphology of the source electrode to improve device performance. We produced three devices with double-layer source electrodes using two kinds of special masks. The thickness for each double-layer source electrode was not uniform. We found that these devices could control the current flow to a certain degree.Finally, three four-layer-source devices were produced. The VOLET device with the structure of ITO/Pentacene (40 nm)/Alq3 (60 nm)/Al (5 nm,13 nm,21 nm,29 nm)/ LiF (150 nm)/Al has the best performance. The Al (5 nm,13 nm,21 nm,29 nm) reflects the thickness of region of one layer to four layers. Furthermore, the thickness of the pentacene layer was optimized to balance carrier injection and improve emission intensity. The optimal thickness of pentacene was found to be 40 nm.