Fabrication And Study Of White Organic Light-emitting Devices Based On Exciplex Emission

Recently, white organic light-emitting diodes (OLEDs) have drawn much attention due to their potential applications in full color displays, in backlight for LCDs, and in solid state lighting sources. The content of this paper is about the fabrication and research of white OLEDs. We aim to solve the problem of complex device structure which resulted in poor reproducibility and high cost. We fabricated a white OLEDs with a simple structure based on exciplexes emission.Firstly, a greenish blue electroluminescent material Zn(BTZ)2 is synthesized and purified. We fabricate a bilayer white OLEDs with a TPD layer as a HTL and a Zn(BTZ)2 layer as a ETL and EML. White light is observed which consisting of the two parts, the one is the exciplexes emission from the interface of TPD and Zn(BTZ)2, the other one is the exciton emission from Zn(BTZ)2 layer. Its CIE coordinates is (0.33, 0.33) at 12V. We study on the effect of thickness of Zn(BTZ)2 layer on carriers recombination zone. When the thickness of Zn(BTZ)2 layer is thicker(80 nm), the electrons and holes recombine in Zn(BTZ)2 layer, when thickness of Zn(BTZ)2 layer is thinner (65 nm), electrons and holes can recombine at the interface of TPD and Zn(BTZ)2 with the form of exciplexes emission, and the others recombine in the Zn(BTZ)2 layer with the from of exciton emission.In order to improved the efficiency of device, fabricate a white OLEDs used LiF/Al as cathode to enhance electrons injection. But the external quantum efficiency (EQ) of device reduced. It can be due to the good ability of electron transporting of Zn(BTZ)2 which resulted in the amout of electrons more than that of holes in the Zn(BTZ)2 layer. So by increasing holes injection, a high EQ device can be obtained. Fabricated a device with a PEDOT:PSS thin film on ITO, and its EQ increased from 0.35% to 0.45%.Phenothiazine (M1) is a well-known heterocyclic compound with electron-rich nitrogen and sulfur heteroatom. It is a excellent p-type conjugated polymers due to its readily injection and transport of hole. Unlike phenothiazine, phenothiazine-5-oxide (M2) is a specific molecular which is good ability of electrons injection because of conversion of electron-donating sulfur atom to electron-withdrawing sulfoxide group. Synthesize two polymer, P1 only contains M1 unit, P4 is consisted of M1 and M2. The EQ of device of P4 is 3.5 times as much as that of P1.During the process of studying white OLED, we fabricate a white OLED, and improve its performance with a PEDOT:PSS modifying the anode. Meantime, we also study a high efficient polymer through introducing a electron-withdrawing unit. There are still some work need to do, such as understanding how does the LiF/Al work to enhance the electron injection, and getting a uniform PEDOT:PSS film to improve the lifetime of device.