Interface Construction Strategy And Application Of Organic Transport Layers In OLEDs

Organic light-emitting devices(OLEDs)exhibit the advantages of low power consumption,high color gamut and wide viewing angle,and thus have been widely applied in full-color display and solid-state lighting.Although electronic products based on OLEDs have been widely used,various problems such as low device efficiency,serious roll-off,and complex structure of multi-color devices still restrict the development of OLEDs.The interface control of OLEDs can effectively improve the above problems.Therefore,we focuse on the interfacial regulation of organic transport layers for different types of OLEDs,including the structural design of color-tunable all-exciplex-based OLEDs,the interface construction between light-emitting layer and transport layer for low-roll-off green fluorescent OLEDs,and the interface construction between the electrode and the organic layer for high-efficiency single-layer phosphorescent OLEDs.The detailed contents are as follows:(1)Color-tunable all-exciplex-based OLEDs with simple structure were designed.Two kinds of electron donor materials TAPC and m CP and electron acceptor material PO-T2T were used to construct two exciplexes.Among them,m CP and PO-T2T were blended to form an exciplex,and the pure TAPC film was located on the left or right interface of the blended film to form an interface exciplex with PO-T2T in the blended film.The electroluminescence of these two exciplexes were blue and yellow,respectively.By optimizing the position and thickness of the pure TAPC film to adjust the color,the all-exciplex-based OLEDs could realize blue,green,yellow,and white emission,respectively.The maximum current efficiency(CE_max)of these devices were 2.85,16.61,8.79,5.55cd/A,respectively.(2)Low roll-off green fluorescent OLEDs were constructed by using electron/hole transport layers matching strategy.In the green fluorescent device based on Alq₃,doped devices and non-doped devices were used to optimize the combination of hole transport materials and electron transport materials.Among them,TAPC,TCTA,NPB/TCTA were used as hole transport materials,and Alq₃,Tm Py PB,TPBi,and BPhen were used as electron transport materials.Finally,devices using TAPC as the hole transport material and BPhen as the electron transport material performed best in terms of carrier balance and exciton confinement,and achieved the highest efficiency and extremely low efficiency roll-off.Among them,the CE_max and efficiency roll-off(@30000 cd/m²)of the doped devices were 10.06 cd/A and 19.3%,respectively,and the CE_max and efficiency roll-off(@30000cd/m²)of the non-doped devices were 7.41 cd/A and 9.5%,respectively.(3)High efficiency single-layer phosphorescent OLEDs were constructed by adjusting the anode/organic layer interface.The single-layer devices using high-concentration doped TPBi:Ir(ppy)₂(acac)as the light-emitting layer were constructed.In order to buffer hole injection and block excitons,while keeping the light-emitting layer away from the electrode,a buffer layer was inserted at the interface between the anode and the organic layer.Five traditional hole transport materials including TCTA,TAPC,CBP,m CP,and NPB were used as buffer layers with a thickness of no more than 10 nm.The use of the buffer layer did not affect the injection of holes from ITO into the highly-doped guest,and the turn-on voltage of the devices were between 2.5 and 2.7 V.At the same time,the buffer layer could effectively reduce the exciton quenching.The CE_max of the devices with TCTA,TAPC,and CBP as the buffer layer were 84.89,80.99,and 79.83 cd/A,respectively,reaching the efficiency level of the multilayer devices.