Charge Transfer State And The Energy Transfer Mechanism In Organic Luminescent Materials And Devices

The charge transfer states are excited states formed by interconnected electron-hole pairs,and have become research hotspots in the fields,such as organic temperature sensing,organic photovoltaic solar cells(OPV)and organic light-emitting diodes(OLEDs).However,the current research of charge transfer states is still relatively limited in organic luminescent fields.And materials and devices could only be designed through the not perfect concept.In this thesis,the charge transfer state and energy transfer are studied in organic luminescent materials and devices.Consequently,the research and application of charge transfer state materials in the fields of organic temperature sensing and OLED are extended.The details are as follows:(1)Using the step function of the metal-metal to ligand charge transfer(MMLCT)states during energy transfers of Pt-BAN-N1,the metal-ligand charge transfer(MLCT)states energy is more efficiently transferred to the triplet excited state of anthracene(~3An)at lower temperatures.Finally,an appropriate linear correlation can be builted between the relative intensity of emission at 708 nm and temperatures.Therefore,the reason for the excellent temperature sensing characteristics of Pt-BAN-N1 is analyzed.Moreover,by photoluminescence spectra,transient spectra and theoretical calculation,the emission peaks at 456 nm in the solution,502 nm and 708 nm in the films are derived from the fluorescence of the ligand,~3MLCT state and ~3An,respectively.(2)Due to the change of the excited states configuration and the strong intermolecular interaction of BNAC-1,the stable intermolecular charge transfer states are formed,generating the emission at 503 nm.Consequently,the triple emission peaks of blue,green and yellow are generated in BNAC-1,derived from anthracene groups,intermolecular charge transfer states and excimers,respectively.Therefore,the results contribute to improve the color rendering index of single molecular white devices.Moreover,by photoluminescence spectra,transient spectra and theoretical calculation of BNAC-1 and BNAC-2,the emission peaks at 423 nm in the solution and 450 nm in the films are originated from anthracene groups,and the emission peak at 560 nm in the films is derived from the excimers,respectively.(3)Based on the charge transfer state materials as hosts of emitting layer,study the devices performance with this structure.Firstly,the charge transfer material DMACNMPTO is used as single host to construct blue,green and yellow TADF devices,which achieve maximum external quantum efficiencies of 18%,18.56%and 19.13%,respectively.And the efficiency roll-off is improved.The results show better devices performance than the devices with traditional host materials.In addition,using the charge transfer state material IndCzpTr-1 as both the blue light emitting guests and the hosts of yellow materials,a pure fluorescent white light device with external quantum efficiency of 14.04%and a hybrid white light device with external quantum efficiency of 21.72%are obtained.(4)Based on m-D15NCzDPA with the high electronic mobility as the electron transport layer material,the exciton quenching in the devices is improved by using the charge transfer state materials as hosts.DMACNMPTO is used as the hosts of blue phosphorescence and TADF materials,and IndCzpTr-1 is used as the hosts of green light,yellow phosphorescence and TADF materials.Compared with the devices of traditional host materials,the efficiencies of the new devices with are greatly improved.And both green and yellow devices achieve ultra-low turn-on voltages of 2.2-2.3 V.(5)Designing a multi-layer doping functional layer structure,fabricate the fluorescent and phosphorescent devices with charge-transfer materials as the assisted guests.In the fluorescent devices,more excitons energy of SFI34pTz is transferred to the common fluorescent material TBRb.As the results,the fluorescent device with multi-layer doping functional layer achieves efficiency improvement of 20%.In the phosphorescent devices,the assisted emitting layers are used to efficiently obtain excitons.Consequently,more excitons energy is transferred from assisted emitting layers to the intrinsic emitting guest PO-01 through efficient Dexter energy transfers between different doping functional layers.Finally,the phosphorescent devices with multi-layer doping functional layer achieve maximum external quantum efficiency of 21.82%.