The Study On Properties And Mechanisms Of Polymer Electroluminescence

Since polymer light-emitting diodes (PLEDs) were invented, much efforts have been made to improve the brightness and efficiency of its electroluminescence for realizing PLED commercial application. We investigated several factors influencing the brightness, efficiency and spectrum characteristics of PLEDs EL, especially focused our attention on the processes of carrier injection, transport, recombination and annihilation factors influencing brightness efficiency of organic electroluminescence(OEL) in doped single and double- layer PLEDs.Firstly,(1)the influence of soluble PPV derivatives mixed with inert matrix photoluminescence (PL) efficiency. We found the reason of PL quenching is inter-chain hopping of excitons. (2) We investigated the influence of electric field on PL intensity in PPV derivatives and Alq. The results showed that carriers in trap and carrier aggregation cause PL quenching. Carrier aggregation on the interface between organic layer and electrodes may screen extra electric field and reduce barrier height for carrier injection.(3)We utilized OXD as buffer layer in anode and LiF in cathode in single layer MEHPPV PLEDs. And the efficiency and brightness was doubled. The results implied that aggregation of minority carriers at the interface may the role of blocking layer. The characteristic of current and voltage was also analysed.Secondly, we demonstrated the possibility of improving electron and hole injection and balance to poly (phenelene vinylene) derivatives by replacing oxadiazole segments.At last, we studied the role of impurities in OEL. The solvent used in different thin film conformation of non-conjugated oligmer,(Alq Oligmer)could influence the luminescent characteristic of PLEDs.It was excellent method for doped impurity in host to improve brightness and efficiency. We investigated transient EL of single-layer PLEDs blended with Alq/PVK, PVK/MEHPPV, Eu Complex /PVK , respectively.The separated phase of blends and carrier injection, transport and decay were firstly investigated by monitoring two different transient EL peaks. We also investigated EL characteristic of double-layer PLEDs, ITO/PVK-DCJTB/Alq/LiF/Al, by similar method. This method was successfully used for getting directly information of carrier injection, accumulation, tunnel and annihilation between two layers. The mutual injection between organic layers and recombination zone can be adjusted by changing the concentration of dopants in blends.