| This dissertation focuses on interface engineering and its influence on organic electronic devices. A comprehensive review of interface studies in organic electronic devices is presented in Chapter 1.; By interface engineering at the cathode contact, an ultra-high efficiency green polymer light emitting diode is demonstrated in Chapter 2. The interface modification turns out to be solution processable by using calcium acetylacetonate, donated by Ca(acac)2. The device structure is Induim Tin Oxide (ITO)/3,4-polyethylenedioxythiophene-polystyrene-sulfonate (PEDOT)/Green polyfluorene/Ca(acac) 2/Al. Based on this structure, we obtained device efficiencies as high as 28 cd/A at 2650 cd/m2, which is about a 3 times improvement over previous devices. The mechanism of this nano-layer has been studied by I-L-V measurements, photovoltaic measurements, XPS/UPS studies, impedance measurements as well as transient EL studies. The interfacial layer plays a crucial role for the efficiency improvement. It is believed to work as a hole blocking layer as well as an electron injection layer. Meanwhile, a systematic study on ITO electrodes is also carried out in Chapter 4. By engineering the interface at ITO electrode, the device lifetime has been improved.; In Chapter 5, very bright white emission PLEDs are fabricated based on blue polyfluorene (PF) doped with 1 wt% 6, 8, 15, 17-tetraphyenyl-1.18, 4.5, 9.10, 13.14-tetrabenzoheptacene (TBH). The maximum luminance exceeds 20,000 cd/m2. The maximum luminance efficiency is 3.55 cd/A at 4228 cd/m2 while the maximum power efficiency is 1.6 lm/W at 310 cd/m2. The white color is achieved by an incomplete energy transfer from blue PF to TBH. The devices show super stable CIE coordinates as a function of current density.; The interface engineering is also applied to memory devices. In Chapter 6, a novel nonvolatile memory device is fabricated by inserting a buffer layer at the anode contact. Devices with the structure of Cu/Buffer-layer/organic layer/Cu show very attractive electrical bi-stability. The switching mechanism is believed to origin from by the different copper ion concentrations in the organic layer. This opens up a promising way to achieve high-performance organic electronic devices. |
