合成以多面體矽氧烷寡聚物為中心核之星狀發光材料及其在電激發光元件之光電性質研究

Abstract

摘要 本研究合成出三種以POSS為中心核，發光基團為分支之星狀發光材料POSS 1 ~ POSS 3。三種發光單體中，其中兩種為OPV衍生物的螢光分子(C-1 ~ C-2)；另一種為銥錯合物的磷光分子(C-3)。這些星狀發光材料是利用POSS中心核之Si-H官能基與含有末端雙鍵的發光基單體，於鉑的催化下進行矽氫化(hydrosilylation)反應而生成。

星狀發光材料POSS 1 ~ POSS 3的吸收及放射光譜皆與發光基單體相似，並不會因POSS的引入而造成發光能隙改變。相較於發光基單體，以POSS為中心核的星狀發光材料具有較高的熱裂解溫度。此外，迴火(annealing)實驗結果發現，星狀發光材料POSS 1 ~ POSS 3之放射光譜皆明顯較發光單體C-1 ~ C-3穩定。這些研究結果顯示藉由導入POSS做為中心核的結構可以提升發光材料的熱性質及光色穩定性。

POSS 1為最大放光波長在476 nm之藍綠光材料，POSS 2為最大放光波長在496 nm之綠光材料，而POSS 3為最大放光波長在524 nm之黃綠光材料。由於此星狀發光材料具有一定的成膜性，故可直接以旋轉塗佈的方式製成元件。將POSS 1、POSS 2製成結構為ITO/PEDOT/POSS n:PVK:PBD/Ca/Al的單層有機電激發光元件，其最大亮度分別為1102 cd/m2及1468 cd/m2，最大量子效率接近1 cd/A；POSS 3以CBP為主體，製成結構為ITO/PEDOT/POSS 3:CBP/LiF/Ca/Al之元件，最大亮度可達1458 cd/m2。將電洞阻擋材料TPBI摻混入POSS 3後，最大量子效率可增加至3.99 cd/A。此外，星狀發光材料之元件於不同電壓下皆仍維持穩定的EL光譜。 最後，利用廣角X光繞射儀(WAXD)及掃描式電子顯微鏡(SEM)來分析星狀發光材料之晶格結構及型態。由WAXD的結果顯示，相較於單純的POSS，奈米晶體POSS 1 ~ POSS 3具有較大的d-spacing；由SEM圖得知，POSS 1 ~ POSS 3形成直徑大小約20 nm的奈米晶形，且其具有均一性的分佈。

Abstract We have synthesized three novel light emitting materials (POSS 1 ~ POSS 3), which utilize polyhedral oligomeric silsesquioxanes (POSS) as the cores to link the chromophores. The chromophores can be fluorescence (C-1, C-2) and phosphorescence (C-3) dyes. These three star-like light emitting materials were synthesized by hydrosilylation of Si-H groups on the POSS cores and the vinyl end group of the chromophores using Pt as catalyst.

POSS 1 ~ POSS 3 have similar absorption and photoluminescent spectra with their corresponding chromophores. It means that the silsesquioxane core does not affect the energy gap of the light emitting materials. The thermal degradation temperatures of POSS 1 ~ POSS 3 are higher than those of chromophores C-1 ~ C-3. Furthermore, the annealing experiments show that the PL spectra of POSS 1 ~ POSS 3 are more stable than those of chromophores C-1 ~ C-3. These results indicate that the incorporation of the silsesquioxane core could enhance the thermal and luminescent stabilities of the obtained light emitting materials.

POSS 1 emitts blue green light at 476 nm, POSS 2 emitts green light at 496 nm, while POSS 3 emitts yellow green light at 524 nm. The star-like light emitting materials show good film forming property. Therefore they can be used to fabricate devices by spin coating process. The single-layer LED devices with the configuration of ITO/PEDOT/POSS n:PVK:PBD/Ca/Al for POSS 1, POSS 2 show maximum brightness of 1102 cd/m2 and 1468 cd/m2 respectively and maximum quantum efficiencies of ca. 1 cd/A. The maximum brightness of the device with the configuration of ITO/PEDOT/POSS 3:CBP/LiF/Ca/Al is 1458 cd/m2. After blending the hole blocking material TPBI with POSS 3, the maximum quantum efficiency can be increased up to 3.99 cd/A. In addition, their EL spectra are stable even at high voltages.

Finally, the crystal structure and morphology of the star-like light emitting materials, POSS 1 ~ POSS 3 were studied by wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). X-ray diffraction results show that the d-spacings of the POSS 1 ~ POSS 3 nanocrystals are larger than that of pure POSS. The SEM analysis reveals that POSS 1 ~ POSS 3 form the nanocrystals with diameter of about 20 nm. The size distribution of the nanocrystals is very uniform.