The Study On The Interface And Well Structure Of Organic Electroluminescences

Comparing to inorganic light-emitting, organic light-emitting has a wide range of material selection, full-color display which is from the blue region to the red light district, low driving voltage, high brightness and efficiency; wide viewing angle, fast response, relatively simple manufacturing process, low cost, flexible displays and so on. Therefore, organic electroluminescences have been rapidly developed in recent years. It is believed to be the mainstream of the next generation of display devices.This paper investigate the influence of well structure on the field-modulated photoluminescence quenching of organic devices, impacting of well structure on the performance of organic electroluminescent devices, as well as the emission properties of the interface between hole transport layer and electron transport layer of organic light emitting devices. The full-text is divided into five chapters. The first two chapters are introducing the background and principle of organic light-emitting devices. The latter three chapters focus on the study of the experiment content. We got some new results in our studies.Firstly, the photoluminescence properties of two different types of organic well structure devices under reverse bias are studied. PBD and Alq3 are used for preparing four kinds of different cycle type-â… well structure devices. The light quenching of multi-cycle well structure devices are weaker than the device have single well structure. Because the potential well layer of type-â… well structure are both of hole and electron potential well. The ionization electrons and holes could be limited in Alq3 layer; they would recombine to form exciton and emission light. But when the well number is larger than 2, the photoluminescence quenching increases as the well number increased under reverse-bias modulation. That is because when the well number becomes too large, the number of interface increases and the thickness of each layer become thinner, which lead to strong photoluminescence quenching. Three different cycles of type-â…¡organic well structure devices have been fabricated by using of NPB and CBP. The photoluminescence properties of these three devices under reverse bias modulation are discussed. The results show that the exciton quenching intensity of NPB layer is faster than the CBP layer. This is because the effective electric field distribute in NPB layer is larger than CBP layer. The exciton quenching intensity both of NPB and CBP layer become larger when the well number increases under the same reverse voltage. That is because the exciton will become more unstable as the cycle of type-â…¡well increase. The impacting of these two different types of well structure on the photoluminescence quenching is also discussed.Then the properties of other five kinds of well structure light-emitting devices have been studied. The impacting of the well number and barrier layer thickness on the device performance has been analyzed. Experimental results show that using of appropriate well number and barrier layer thickness can improve the brightness and efficiency of the devices. Then we use NPB and Alq3 composed well structure as the hole transport layer, and using Alq3 and BCP consisting of well structure as the electron transport layer for improving the device performance. The impacting of well number on the device performance has been analyzed. The experimental results show that when using of well structure as electron transport layer are better than using of it as hole transport layer.Finally, we studied the exciplex and electroplex emission from the interface of TPD and BCP layers through preparation of different structure devices. Under different driving voltages, the electroluminescence spectra of device ITO/TPD/BCP/Alq3/Al have four emission peaks, locating at 401,425,452 and 480 nm. The 401 and 425 nm emission peaks are the exciton emission of TPD molecules. The characteristics of 452 and 480 nm emission peaks are discussed. The experimental result show that the 452 nm emission peak belongs to singlet local state exciplex emission, and the 480nm belongs to singlet charge transfer state exciplex emission. Then we discuss the two new emission peak 590 and 630 nm from the electroluminescence spectra of the device ITO/TPD/BCP/Rubrene/BCP/Alq3/LiF/Al. The 590 nm emission is the triplet state exciplex emission, while the 630 nm is the electroplex emission from the interface of TPD and BCP.