Study Of The Luminescence Properties Of Organic Multiple Quantum Well Structures

In 1987, C.W. Tang reported the double-layer electroluminescent diode with high brightness, efficiency and low driven voltage. This breakthrough made the research of organic electroluminescent diodes (OLEDs) spread widely through the world, which has developed deeply since then. In 1989, Forrest et al first brought forward the conception of organic multilayer quantum well structure (OMQWs), which has the characteristics of high emission efficiency, narrowed emission band, tunable emission region and enhanced carriers balance, however, some essential problems still need to be solvedAiming to discuss these basic problems of OMQWs, we study OLEDs with quantum well structures as transporting layer, the energy transfer and blue shift in the photoluminescence (PL) by the use of small angle XRD and conventional opto-electronic measurement techniques and then get some significant results.1. Small angle XRD spectra show that the samples prepared have good layer structure.2. We fabricated the devices with OMQWs, which consisted of alternative NPB and CBP and acted as hole-transporting layer. NPB acts as potential well for the holes and CBP does as potential barrier. Compared with conventional devices, the enhanced luminescent properties of OLEDs are obtained. The device with 2-period quantum well got the maximum brightness and efficiency. The results demonstrate that CBP potential barriers effectively block the holes transportation, reduce the number of carriers arriving at the luminescent region and further enhance the balance of holes and electrons.3. Compared to the double-layer, the OMQWs conduce to the energy transfer from barrier layers to well layers. For the PBD/Alq₃ OMQWs with different periods, the optimum period number is 3 at the maximum energy transfer rate. For the OMQWs with different materials, it can be obtained that the energy from PBD and BCP transfer completely to Alq₃ in PBD/Alq₃ and BCP/ Alq₃ quantum well structures, respectively. However, in NPB/ Alq₃ quantum well structure, the energy from NPB transfers partly to the Alq₃. Because the energy transfer between two materials in OMQWs is Forster energy transfer, the energy transfer is mainly dependent on the overlap between the PL spectra of donor molecule and the absorption spectra of acceptor molecule.4. In the PBD/Alq₃ double-layer and PBD/Alq₃/PBD quantum well structures with different Alq₃ layer thickness, there exists blue shift of Alq₃ emission peak in both of such PL spectra as the thickness of potential well layer is decreased. It indicates that the...