The Study On Solution-processed Oxide And Hybrid Light-emitting Field-effect Transistor

Thin film transistors(TFTs),as the key device of active matrix flat panel displays,have electrical signal processing,control,and transmission capabilities.TFTs based oxide semiconductor have been widespread concerned because of a series of advantages,including high carrier mobility,excellent visible light transmittance,extremely low off-state current,and good large-area uniformity.However,it limits further commercial application of oxide TFTs that relatively high production cost seriously and the instability which experienced a negative gate bias stress combined with continuous illumination/heat(NBI/TS).Rare earth elements are used in many fields,especially lanthanides(Ln)which have rich and unique photoelectric properties.In this paper,we studied the effect of different rare earth elements doping on the photostability of oxide TFT.It found that the part of blue light of LED was absorbed and converted to non-radiative transition by using the charge transfer effect of Pr⁴⁺and Tb⁴⁺,which greatly improves the NBIS stability of oxide TFT.Then,the application of rare earth doped oxide semiconductor in LET was studied.It is beneficial to improve the luminous efficiency,stability and lifetime of LET that using Sc:In₂O₃ semiconductor formed by doping Sc₂O₃ into In₂O₃ as the electron transport layer of light-emitting field-effect transistor(LET),for taking advantage of the insensitivity of rare earth oxide Sc₂O₃ to water vapor and visible light.The performances of TFTs(Ln:In₂O₃ TFT)based on solution-processed Ln-doped(except for radioactive Pm)indium oxide semiconductors have been systematically studied.All Ln:In₂O₃ TFT(except for Ce:In₂O₃)with 5 at%doping all exhibit good TFT characteristics,which makes the turn-on voltage of the devices drift from-13.8 V of pure In₂O₃ TFT to the range of-1?1 V,reflecting the strong oxygen vacancy suppression of lanthanides.More interestingly,compared with other Ln,Pr and Tb doping can better improve the NBIS stability of oxide TFT,which is attributed to the charge transfer between Pr and Tb and the ligand ions.This process will absorb the blue part of the LED light and release energy in the form of nonradiative transitions,which avoiding the excitation of the oxygen vacancy electrons by the blue light.Therefore,the threshold voltage shift of Pr:In₂O₃ and Tb:In₂O₃ TFT are only-3.0 V under the combined action of 250 Lux LED white light and-20 V gate bias,without any passivation treatment,while other Ln:In₂O₃ TFTs are the range of-7.9 to-15.6 V.As a new type of multifunctional optoelectronic device,LET can realize the functions of switch control and self-luminescence in a single device,which can effectively simplify the pixel circuit and lower the cost of display manufacturing.In this work,a high-performance,solution-processed hybrid quantum dot light-emitting field-effect transistor(QD-HLET)was successfully prepared by combining Sc:In₂O₃ with high carrier mobility as the electron transport layer and a core-shell structure quantum dot with high luminous efficiency as the light-emitting layer,which achieved an external quantum efficiency(EQE)of 8.7%and an electron mobility of 0.8 cm²V^-1s^-1,as well as a good electrical and optical on/off ratio.Further,a QD-HLET device with an EQE of 22.8%,an electron mobility of 3.1 cm²V^-1s^-1and an electrical/optical switching ratio of 10⁵ is demonstrated by using a bottom gate and non-coplanar asymmetric source/drain electrode structure to enhance effective electron/hole injection,and combining with Sc:In₂O₃/Zn O heterojunction as the electron transport layer and red quantum dots as the light-emitting layer realizes.Such excellent performances benefit from a reasonable device design,a matched energy level structure,and the modulation of the electron concentration in the heterojunction by the gate.Meanwhile,the device exhibits different optical and electrical characteristics in different operating modes,so that the operating mechanism of the LET has been deeply studied.The operating stability differences of the devices under different gate voltages were tested,and a T₅₀ lifetime of 153000 h was obtained.Then,the influence of different hole transport layer materials on the performances of QD-HLET was studied,and the preparation of high-performance and solution-processed QD-HLET was achieved by using orthogonal solvents.Further,the heterojunction band structure is optimized to improve the electron injection at low current density and improve the performance of QD-HLET devices,by controlling the thickness of Sc:In₂O₃.And an electron mobility of 2.7cm²V^-1s^-1,a maximum brightness of 129000 cd/m²,an EQE peak of 18.5%,and a T₅₀ life of8000 hours at 100 cd/m² are achieved.Based on the above research,a dual control model of electron and hole injection is proposed to explain the origin of high luminous efficiency of LET.