Designing Efficient Phosphorescent OLED Materials Synthesis Research, And Performance

Over two decades’ development, OLED technology has gradually perfected itself.Smart gadgets featuring OLED display have already made to market. In solid lightingindustry, OLED lighting panels are in the dawn of mass production. Although OLEDtechnology has already been successfully commercialized, there are still many challengesto tackle, such as materials development, device design and electronic process. OLED isstill one of the hottest research areas in organic electronics. In this thesis, we mainly focuson the design of novel host materials for blue phosphorescent OLED (PHOLED). Andtriphenylamine annulated fluorene and aryl silane were selected from numerousstructures for host materials as the basic backbone in our research. Several series novelmaterials were designed and synthesized using different functional groups and anchoringpositions. All these materials were fully characterized. PHOLED were fabricated usingthese materials as host materials. In addition, some materials were also explored asblocking layer or hole transport layer. Detailed research contents are listed as follow.(1) In chapter1and2, a brief history and current research status of OLED wereintroduced. Then, OLED technology was fully covered from the aspects of basic theory,device structure, physical parameters and materials. And host materials were fullyreviewed by chemical structures and charge transport properties.(2) Inchapter3and4,fournovelhostmaterialsweredesignedandsynthesizedusingtriphenylamine annulated fluorene as the basic structure. Unconjugated triphenyl silaneand diphenyl phosphine oxide were introduced to the C2or C2, C7position as functionalgroups. The triplet energy of the backbone was successfully preserved usingunconjugated functional groups. And, the charge transport property was tuned by thenumberoffunctional groups.Thesematerials were fullycharacterizedandbluePHOLEDdevices were fabricated using them as host materials. Mono-substituted materials showedbetter devices performance. To further exploit the potential of the mono-substituted materials, white PHOLEDs were made and excellent results were obtained.(3) In chapter5, we continued the study of triphenyl silane and diphenylphosphinoxide functionalized materials. In order to further increase the triplet energy ofthe material, the anchoring point was moved to C3on fluorene ring. As a result, twomaterialswithhightripletenergyweresuccessfullyobtained.ComparedtoC2substitutedones in the last two chapters, the triplet energy of these C3substituted materials are0.1eV higher. After the fully characterization of their chemical and physical properties,highly efficient blue PHOLEDs featuring two different dopants were fabricated usingthem as host materials.(4) In chapter6and7, three more C3substituted materials were synthesized withdiphenylamine, cabarzole and phenyl cabarzole as functional groups. These materials arehole transport host materials. And despite the functional were connected to the triphenylannulated fluorene via conjugated bond, these molecules still exhibit high triplet energylevels, sufficient enough to be used as blue host materials. The phenyl cabarzolesubstituted molecule, bearing similar configuration as the3,3’-bicabazole, showed bothhigh triplet energy and high hole mobility, which result in its excellent deviceperformance. On the other hand, diphenyl and cabarzole substituted materials show hightriplet energy and relatively high LUMO level, which make them possible candidates notonly for host materials, but also electron/exciton blocking materials. And in devicefabrication, they were used as host and as blocking layer, resulting in very goodperformance.(5) In chapter8, the molecule structures in chapter7were modified by replacing thetriphenylamineinthespirostructurewithphenylcabarzole.Duetothemorerigidstructureof cabarbole, the glass transition temperatures of these materials were higher. The tripletenergy of these materials are still very high. Blue PHOLED results suggest that they aregood candidates of host materials.(6) Since the triphenylamine annulated fluorene has very good hole transport abilityand high thermal stability, a series of hole transport materials were synthesized in chapter9.N-phenyl-1-naphthylamineand methoxyldiphenylaminewereintroducedonC2orC2, C7position to enhance the hole transport of the material. And in the meantime, theHOMO levels were raised, facilitating holeinjection.As expected, these materials exhibitvery good hole mobility and high Tg. The2,7-N-phenyl-1-naphthylamine substitutedmaterial showed better device performance than NPB as hole transport material.(7) In chapter10, tetraaryl silane was selected as the main structure. A series silanebased host materials were synthesized, incorporating dibenzothiophene, dibenzofuranand pyridine. All the materials were fully characterized. Due the relatively lower tripletenergy, these materials were evaluated as green phosphorescent hosts and excellentresults were obtained.