Static Induction-type Organic Light-emitting Transistors

Organic light-emitting transistor (OLET) integrates the controlling part (i.e. OTFT) and the light-emitting part (i.e. OLED) into one device, using gate voltage to control current, and thereby to control the light emission. In this way, OLET can not only improve the device integration, simplifying the fabrication process, but also improve use efficiency of energy.In this dissertation, the optoelectronic properties and the operation principle of the static induction-type OLET (SIT-OLET) were systematically investigated.Firstly, a SIT-OLET ITO/TPD(50 nm)/Al(30 nm)/TPD(30 nm)/Alq₃(55 nm)/Al in which TPD as hole-transporting layer was made. Our experimental data showed that it is a good Schottky barrier between gate Al electrode and TPD film, and emission from Alq₃ dominates the spectra of the SIT-OLET, peaking at about 530nm. The devices behavior in depletion mode with increasing applied gate voltages, and its emission intensity decreases as source-drain current decreases.Secondly, a SIT-OLET ITO/NPB(30nm)/Al(30nm)/NPB(20nm)/Alq₃(55nm)/Al in which NPB as the hole-transporting layer was fabricated. We found that the SIT-OLET behaviors in an enhanced mode, both the emission intensity of the device and the source-drain current increases with increasing the gate voltages. After analyzing the significant influence of the thickness of the NPB layer, as well as the thickness and shape of the gate, on the performance of the device, optimized device parameters were obtained: a thickness of 40nm for the first NPB layer and 30nm for the comb-shape gate layer.In order to study the carriers injection from gate, we inserted hole-transporting layer BCP at both sides of gate layer and made three kinds of devices ITO/NPB(40nm)/BCP(5nm)/Al(30nm)/NPB(20nm)/Alq₃(55nm)/Al, ITO/NPB(40nm)/ Al(30nm)/BCP(5nm)/NPB(20nm)/Alq₃(55nm)/Al and ITO/NPB(40nm)/BCP(5nm)/ Al(30nm)/BCP(5nm)/NPB(20nm)/Alq₃(55nm)/Al. Our experimental data confirmed the contribution of holes injection from gate to the channel current. Obviously, the balance of charge carriers cannot be improved by insetting thin BCP layer (5nm) to improve luminescent efficiency of these devices.At last, in order to investigate the effect of interface levels on device performance and to improve the controlling ability of applied gate voltages, we fabricated device ITO/NPB(40nm)/Al(30nm)/NPB(20nm)/Alq₃:DCJTB(2wt.%) (55nm)/Al in which Alq₃:DCJTB(2wt.%) with higher luminescent efficiency as active/emissive layer, and we found that the drain current is still very large. Therefore, by insetting another 1nm LiF layer before Al drain electrode, we made another SIT-OLET device ITO/NPB(40nm)/Al(30nm)/NPB(20nm)/Alq₃:DCJTB(2wt.%)(55nm)/LiF(1nm)Al and found that the controlling ability of gate electrode on the emission was significantly increased, and the device emission intensity can be enhanced by three orders of magnitude, implying a SIT-OLET with high properties was obtained.