The Design Synthesis And Optoelectronic Properties Of Organic Wide-band-gap Semiconductors Besed On Tetraphenylsilane

Wide-band-gap materials generally possess band gap larger than3.0eV which canabsorb and emit deep blue or ultraviolet (UV) light. With such high energy, thesematerials are usually applied to UV light emitting diodes (LEDs), UV detection, andespecially to organic light emitting diodes (OLEDs). They can either be used asexcitation sources to active light with low energy such as blue, green and red or ashost matrixes for fluorescent and phosphorescent dyes.Compared with their inorganic counterparts, organic semiconductors have moreadvantages. For example finely adjusted photoelectric properties resulting from easysynthesis and modulation, diversified film forming technics such as vacuumdeposition, solution possessing and flexible display. So the organic materials areconsiderable materials for the future.Suffered from characteristic wide band gap, organic wide-band-gap materialsusually have high lying LUMO energy and low lying HOMO energy level leading topoor electron and hole injecting and transporting properties. The introduction of donorand acceptor unit to optimize the charge injection and transporting properties creates anew problem reduced bandgap caused by uncontrollable intramolecular chargetransfer. In this thesis, we are searching for excellent wide-band-gap materials systemand mudulating the thermal, morphological, photophysical, electrochemical andelectroluminescent properties. For one hand we develop new materials and fabricatedevices with high efficiency, on the other hand we reveal the natural properties ofthese materials.In Chapter2three wide-band-gap cores were chosen to verify which one was the best for constructing wide-band-gap materials. Donor and acceptor units wereintroduced in these three cores. Different cores led to different advantages. Thediphenylether cored materials were the most easily to synthesis caused by simplestructures. The fluorene cored compounds possessed the highest thermal stabilityresulting from rigid framework. The tetraphenylsilane cored molecules had the mostexcellent device performances because of favorable electron affinity and stablemorphology. The result revealed the best choice for constructing wide-band-gapmaterials were tetraphenysilane core.In the next chapter, we optimized the electrical properties according to theprevious work. Wide-band-gap donor carbazole unit and acceptor groupdiphenylphosphrine oxide (PO) were substituted on tetraphenylsilane core. And wealso adjust the numbers and link fashion of carbazole to tune the balance of electronand hole fluxes. Finally we found the combination of carbazole dimer and PO unitwas the best for electroluminescent properties. DCzSiPO based FIrpic doped deviceachieved the highest current efficiency and EQE of24.6cd/A and11.2%respectively.To further test the application of wide-band-gap materials in OLEDs, twosilicon-cored wide bandgap materials were used as electron and hole transportinglayer. Compared to the classic materials wide bandgap materials reached highefficiency of49.4cd/A and27.5%, respectively. The high efficiency indicated theimportance of wide-band-gap materials in OLEDs. Moreover, we found that carbazoledimer unit was better than sole carbazole group as donor unit.In Chapter3, we endowed tetrphenylsilane blue emitting properties bycombination of phenanthro[9,10-d]imidazole unit which was considered to be highefficient blue emitting group and excellent electron transporting unit. According to thecharacteristics of separation of electrical and optical band-gap, we selectivelymodulating the hole affinity without changing the optical properties ofphenanthro[9,10-d]imidazole substituted silanes by combination of carbazole group.We developed one high efficient molecule named DCzSiPPIM. The undoped devicebase on DCzSiPPIM achieved high EQE of3.5%and high utilization of exitons of26.1%which reached the limit of local fluorescent materials. In the next chapter, in order to apply in solution-possessing device, we furtheroptimize the thermal and morphological properties. Two tetraphenylsilane cores wereintroduced to construct compounds. According to the previous work we still usedcarbazole and PO unit to modulate the electrical properties. One extra hole unit wereadded to overcome the problem of lacking of hole flux in solution-possessing device.The introduction of double tetraphenylsilane centers greatly improved the thermal andmorphological properties without changing the optical and electrical properties. Thedoping device based on DCS2PO host materials achieved high current efficiency of26.5cd/A which was two times higher than that of device based on its singlecounterpart. All the result revealed the neutral property of silane.