Study Of Organic Light-emitting Devices Based On Novel Fluorene Small Molecular Materials

Organic light-emitting diodes(OLEDs),which have high potential as the mostideal and potential display technology in the 21^st century,possess many advantages,e.g.,self-emission,fast response,full solid device,easy fabrication,high efficiency,wideview-angle,ultrathin thickness.However,organic materials with high light-emittingefficiency and stability hinder OLEDs from large scale production.The performance ofgreen emitting materials is the highest in primary colors,and that of blue emittingmaterials is the lowest.Aiming at those problems,some hole transporting materials andhole blocking materials have been characterized,and some novel blue emitting fluorenesmall molecule materials and devices have been systematically investigated in thiswork.1.The thickness effects of emitting layer(EML) on the performances of holetransporting layer(HTL)/EML double-layer devices were investigated.Then severalnovel hole transporting materials and boron hole blocking complexes were comparedwith normal assistant materials.The results showed that the four derivatives of TPDcontaining fluorene framework had nothing on TPD except their glass-transitiontemperature(Tg) were almost 20℃higher than TPD.Whereas high performancesdevice with double HTLs(TPF-OMe/TPD) was obtained,that had the maximumefficiency of 1.06 lm/W at 4.5 V.In addition,DMBSB material with double bond hadexcellent hole blocking capability just like BCP,and DMBPA material with triple bondhad inferior hole blocking capability.2.White OLEDs(WOLEDs) were fabricated with non-doped structure based onthe F(o|¨)rster energy transfer from the starburst configuration HKEthFLYPh material toNPB,Alq₃ or Rubrene.The WOLED with structure of NPB/HKEthFLYPh/Alq₃ wasobtained with the highest luminance of 8800 cd/m² at 15 V,the maximum luminanceefficiency of 1.0 lm/W at 5.5 V and the maximum current efficiency of 1.8 cd/A at 5.5 V,and which showed a stable current efficiency.Furthermore,pure WOLED withCommission Internationale de L'Eclairage chromaticity(CIE) coordinates of(0.34,0.33)were obtained by introducing Rubrene yellow dye and optimizing device structure. 3.Aiming at the emission instability of fluorene blue emitting materials viz.lowenergy emission,using the conjugated configuration BFLBBFLYQ material as a probe,the performances of materials and devices based on films by spin-coating method andvacuum evaporated deposition were studied via UV-Vis absorption,photoluminescence(PL),electroluminescence(EL) and Fourier-transform infrared(FTIR) spectra.Theresults showed that fluorenone defects were the origin of low energy emission and theformations of aggregate and excimer were excluded.Moreover the chromism ofBFLBBFLYQ:TPD blend in chloroform polar solvent upon UV irradiation and exciplexemission in BFLBBFLYQ:TPD film were observed and discussed.4.The emission properties of fluorene small molecules with Fluorine(F)auxochrome were investigated.The absorption,PL and EL spectra of materials had ared-shift phenomenon by increasing the number of F substituents,and the turn-onvoltage of device decreased,current density increased,luminance and luminousefficiency were improved.The exciplex emissions were formed between the fluorenemolecule and NPB.Pure and stable blue light of fluorene materials were obtained byinserting CBP layer at the organic interface.Otherwise,the color-tunable OLEDs andWOLEDs were fabricated based on exciplex emissions.In summary,this work paves the way for novel fluorene materials design and highstability and efficiency OLEDs fabrication based on the research focusing on theinstability of light-emitting properties of fluorene small molecules.And this workprovides some powerful evidences and references for further study on devicemechanism and high performance OLEDs via the design of double HTLs,thefabrication of non-doped triple-layer WOLEDs,and the method of eliminating theexciplex emission using CBP material.