High Efficiency Thermally Activated Delayed Fluorescence Oleds,Organic Near-Infrared Photodetectors And Their Integraded Up-Conversion Electroluminescent Devices

Organic optoelectronic devices have attracted more and more attention due to their abundant in materials,lightweight,simple manufacturing process,low cost,integratable with large area and flexible substrates,and easy adjustable photoelectric properties.In this thesis,we first focus on high performance thermally activated delayed fluorescence OLEDs?TADF-OLEDs?and organic near-infrared photodetectors?NIR-OPDs?unit devices,and then construct all organic near-infrared to visible up-conversion electroluminescence devices based on these unit devices.The main research is listed as follows:1.Preparation of highly efficient TADF-OLEDs.Firstly,the effects of the electron transport layers on the performance of non-doped TADF-OLEDs are investigated.DPEPO and Bphen are used as the electron transport layers?ETLs?in the ITO/NPB?30 nm?/2PXZ-OXD?30 nm?/ETL?30 nm?/LiF?1 nm?/Al devices,and it is found that the energy level and carrier mobility of the ETL play important roles in determining the performance of the devices.With a 30 nm Bphen as the ETL,the device shows a brightness of 199 cd/m² at 3 V bias,which is one of the highest values among the reported non-doped TADF-OLEDs.And then CuI is adopted as the hole injection layer for the devices,which results in the improved hole injection property and hence a balanced hole and electron injection in the emitting layer.The optimized device exhibits a luminescence of 1317 cd/m² at 3 V,which is the highest value among the reported non-doped TADF-OLEDs.At the same time,the efficiency roll-off is also improved significantly,and the efficiency at 1000 cd/m² only decreases by 3.02%from its maximum one.Secondly,the effects of n-type PbI₂ anode buffer layer on the performance of exciplex OLEDs are investigated.In the devices based on TCTA:PO-T2T and mCP:PO-T2T exciplexes,the turn-on voltage,power efficiency,and external quantum efficiency are significant improved after introducing the PbI₂buffer layer.It is found that the n-type PbI₂ forms hole injection through a“charge generation”mechanism at the PbI₂/TCTA interface or the PbI₂/mCP interface,which reducing the hole injection barrier at the interfaces.2.Preparation of high efficiency NIR-OPDs.Firstly,PbPc/C₆₀ planar heterojunction?PHJ?is used as the photoactive layer.The effects of the n-type PbI₂anode buffer layer on the performance of the NIR-OPDs are studied.Compared with the device without an anode buffer layer,the external quantum efficiency?EQE?of the device at 900 nm increases from 10.5%to 26.7%while the specific detectivity increases from 1.6×10¹¹ Jones to 9.96×10¹¹ Jones.On the one hand,the improvement is attributed to the enhanced hole collection efficiency.On the other hand,the templating effect of PbI₂ leads to the preferred growth of the triclinic phase PbPc in the film,which increases the NIR absorption efficiency of the device.Further studied reveals that the hole collection process of the device is through the charge recombination mechanism at the PbI₂/DBP interface.Similarly,PbI₂ can be used as an anode buffer layer for organic solar cells.The power conversion efficiency and stability of the organic solar cells based on DBP/C₇₀ are remarkably improved.Secondly,the effects of charge traps on the performance of near-infrared photodetectors based on PbPc/C₆₀ PHJ is studied.It is found that the photomultiplication effect of the photoconductive type and trap-assisted carrier tunneling injection type photodetectors are achieved by the capture and accumulation of the photogenerated carriers in the charge traps,which break the neutral balance of the device.Through optimizing the device structure,a NIR-OPD with an EQE higher than 10,000%can be achieved.3.Preparation of high efficiency non-doped all organic NIR-to-visible up-conversion devices.The photomultiplication NIR-OPD is integrated with the highly efficient non-doped TADF-OLED to construct an up-conversion electroluminescence device,which realizes a NIR-to-visible up-conversion electroluminescence with excellent performance.Under a 0.052 mW/cm² 808 nm NIR illuminations,the photon-to-photon up-conversion efficiency of the device reaches256%,and this is the first time that the up-conversion efficiency exceeds 100%for an upconversion electroluminescence device based on a photodetector/LED combination structure.At the same time,the optical power conversion efficiency of the device is as high as 398%.It is found that the high up-conversion efficiency is mainly attributed to the photomultiplication mechanism of the NIR-OPD unit,that is,the near-infrared photodetector unit has a photoelectric conversion efficiency up to 1.95×10⁴%.Then a large-area up-conversion imaging device is prepared,and visible light images that can be directly captured by naked eyes and digital cameras.Besides,the device has the advantages of high response speed,high contrast,and high resolution.