Study On Control Of Energy And Charge Carriers In Organic Light-Emitting Devices

The development of organic light emitting device and materials has been the subject of intense academic and industrial research due to their potential application of full-color flat panel displays.The objectives of this dissertation are mainly focused on controlling the procedures of carrier injection, transportation, and recombination in organic light emitting device. The main results are obtained as follows:1. A blended layer composed of a coil-rod-coil triblock oligomer (PEO-b-PHP-b-PEO) and LiCF3SO3 was introduced into light-emitting electrochemical cells as hole injection/electron blocking material. The introduction of the blend layer improves the device's response rate and carrier's combination efficiency at the active layer. A high level of efficiency of 2.05 cd/A, 1.51 lm/W, 2.6% can be achieved by the double-layer device.2. By the simple stacking, we combined the organic light-emitting principle and the electrochemiluminescent principle into one complexed device. By adjusting driving bias or polarity, the procedures of carrier injection, transportation, and recombination can be controlled, thus controllable multi-color emission was achieved.3. We constructed symmetrical structured device by employing 2',2',2'(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) as hole blocking layer and a blue light emitting material (poly(9,9-dihexylfluorene)) with good bipolar transporting ability as an emissive layer. Tri(8-hydroquinoline)aluminum (Alq3), 5,6,11,12-tetraphenylnathacene (rubrene) and SMTPA were utilized as green, yellow and red emitting materials separately. Polarity-controlled blue-green, blue-yellow and blue-red multicolor emitting was realized.4. Highly efficient OLEDs based on three kinds of novel phosphorescent dyes (as the guest materials) were fabricated. The relationships between the device structures, doping concentration, thickness of electron transporting layer, and the device properties are systematically studied. The device with (PPM)2Ir(acac) as the dopant and CBP as the host showed a maximum external quantum efficiency of 13.9% and current efficiency of 58.2 cd/A, which is so far the highest values among the phosphorescent device.