Study On Enhancing Performance Of Organic Light-emitting Devices By Utilizing Tandem Structure

Tandem organic light-emitting diode (OLED) generally consists of severalelectroluminescent units through charge generation layer (CGL). Compared tosingle-emissive-unit OLED, tandem OLED has received much attention in solid-state lightingdue to their have higher luminance, higher current efficiency, long lifetime and better colorstability, which is OLED with the most effective structures for high performance OLED.However, there is a problem of low power efficiency in tandem OLED. This thesis mainlyrevolves around founding new material or structure for charge generation layer to achievepower efficiency enhancement of OLED. The details are as follow:1. The injection and transport characteristics of electrons are enhanced by using a noveln-type dopant NaCl doped into Bphen to form n-type doping layer Bphen:NaCl, whichimproves the carriers balance and the exciton utilization rate in OLED and thus enhancesdevice efficiency. And simultaneously the doping mechanisms of NaCl is investigated.2. The introduction of a n-type doping layer Bphen:NaCl in tandem OLED. First, themechanisms of the effective CGL of Bphen:NaCl (6wt%)/MoO3are discussed by analyzingtheir relevant energy levels and carrier transporting characteristics. Meanwhile, theBphen:NaCl (20wt%) layer was used as the electron injection layer by combining the CGL tofurther improve the performance of tandem device. Thus, the maximal current efficiency andthe maximal power efficiency of tandem device are enhanced approximately by2.1and1.1times compared with those of the single-emissive-unit device, respectively. We attribute thisimprovement to the increase of electron injection ability by introducing of Bphen:NaCl layer.3. The high efficient blue fluorescent tandem OLED based on the CGL ofC60/rubrene:MoO3was fabricated. Meanwhile, the LiF/Al was used as electron injection layerto further increase electron injection from CGL to adjacent emission unit. For this tandemdevice, the maximal current efficiency of32.3cd/A and the maximal power efficiency of11.1lm/W are obtained, which are enhanced approximately by2.3and1.2times compared withthose of the single-emissive-unit device, respectively. Then, tandem white OLED based onLiF/Al/C60/rubrene:MoO3is fabricated, there are a stable white emission spectra and CIEcoordinates due to the balanced injection of the electrons and holes from CGL to two sidesemission unit.