The Study On Structures, Materials, Properties And Mechanisms Of Organic-inorganic Heterojunction Electroluminescence

Electroluminescence (EL) is a phenomenon of direct transformation of electric energy into light. It has several preferences, such as emissive. wide view angle,quick response, Wide working temperature range, high pixel resolution, anti-strike etc. All these properties make it more easily to be applied in flat panel displays than other displays technologies such as LCD, LED, PDP, FED etc. To obtain an excellent EL device, some attempts have been done to fabricate organic-inorganic heterostucture EL device. The organic-inorganic heterostucture EL device is a new approach to construct high performance EL device taking advantage of both the organic and inorganic semiconductors.The main work of this Ph.D. dissertation was focused on properties and mechanisms of Organic-inorganic heterojuction EL device, investigating how to fabricate an efficient EL device with organic-inorganic heterostructure. Not only using the primal properties but also using the secondary properties of inorganic material such as electron multiplication and acceleration, we studied the cathodoluminescence-like emission.Firstly, we utilize the inorganic materials to improve the carrier injection and therefore improve the emission brightness and efficiency of OEL.(1) Using LiF as buffer layer and PF as emission layer, we fabricate an organic-inorganic heterostructure EL device. Comparing with other materials ( such as ZnS, Ta₂O₅), we think, on the interface LiF/PF there is charge transfer. Based on the interface dipole model, we interpreted the improvement of carrier injection by using LiF as buffer layer.(2) Using II-VI semiconductor materials as electron transport layer, MEH-PPV as emission layer, we fabricated an organic-inorganic heterostructure EL device. The conduction mechanism of the device is studied. The interfacial barrier implies interfacial charge accumulation, which result in a significant redistribution of the electric field and improvement of balance of two kinds of charge carriers.Secondly, we fabricated an organic-inorganic heterostructure EL device with organic material PVK and II-VI semiconductor ZnSe. Blue light emission of ZnSe thin film from the ZnSe/ PVK heterostructures was obtained. The EL mechanism of the hybrid device is the injectionand recombination of the carriers. The PVK layer improves holes injection. By changing the thickness of organic layer and emission materials, we studied the factors that influence the emission mechanism of the organic-inorganic heterstructure device. We have fabricated a novel white organic-inorganic heterostructure EL device with organic material PF and inorganic materials ZnS:Mn. the emission mechanism of which was also studied.At last, using the secondary properties of inorganic material such as electron multiplication and acceleration, we studied the cathodoluminescence-like emission.(1) Using Ta2O5 as electrons acceleration layer and MEH-PPV as emission layer, we fabricated an organic-inorganic heterostructure device. There also appears the cathodoluminescence-like emission, which means the CL-like emission not only can be observed by using SiC>2 as electrons acceleration layer but also can be observed by using other materials as long as it can accelerate electrons such as Ta2O5.(2) Using SiO2 as electrons acceleration layer and ZnSe as emission layer, we fabricated an EL device. By changing thickness of ZnSe layer, we explain the emission of ZnSe layer due to the bombardment of hot electrons that accelerated bu SiO2 layer in the strong electric field. It is said that the CL-like emission is not only can be observed by using organic materials but also can be observed using inorganic materials.