| In recent years,in the field of optoelectronics,perovskite light-emitting diodes(PeLEDs)has become a hot research object.Halide perovskite materials have the characteristics of high carrier mobility,adjustable band gap,narrow half-height width,high luminous color purity,wide color gamut,low preparation cost and simple preparation process.However,when the theoretical internal quantum efficiency(IQE)is close to 100%,so far,the highest external quantum efficiency(EQE)of PeLED is only 28.1%.It has been found that the PeLED’s EQE is seriously limited by the low light extraction efficiency.A large number of photons are trapped in the device due to the substrate mode,optical waveguide mode,surface plasmon mode and metal absorption mode,which result in re-absorption of photons in the device.The photons trapped in the device are converted into heat energy,which will damage the device,resulting in poor carrier transmission performance,low water and oxygen resistance performance,and poor stability of the device.Therefore,the improvement of light extraction efficiency is important for PeLED devices.In this thesis,the research is carried out from two aspects:simulation and experimental preparation of devices.Under the guidance of simulation,PeLED devices with high light extraction efficiency are prepared.The content of the thesis is as follows:Considering the problem of low light extraction efficiency caused by poor refractive index matching between the perovskite film and the hole transport layer(HTL)in the device,NiO_x is used instead of PEDOT:PSS as HTL.Considering the refractive index mismatch between ITO and glass substrate,high refractive index substrate is used to replace glass substrate.Considering the low efficiency of light extraction at the interface between high refractive index substrate and air,microstructure is introduced on the substrate by forming patterned sapphire substrate(PSS).Firstly,devices with different structures are designed and simulated.From the perspective of geometrical optics,monte Carlo algorithm is used to simulate them.It is found in devices,NiO_x as HTL has better light extraction performance than PEDOT:PSS as HTL.PSS is more conducive to export the trapped photons in the substrate mode than flat glass substrate.As the thickness of each layer of film is tens of nanometers to about 100 nanometers,the influence of wave optics must be considered.Finite difference time domain method(FDTD)is an algorithm considering wave optics,therefore,it is used to study the light extraction efficiency of devices with different structures in optical waveguide mode.It is found that NiO_x as HTL is more conducive to export photons from the emissive Layer to the ITO layer than PEDOT:PSS.Compared with flat glass substrate,sapphire substrate is more conducive to introduce photons from ITO into the substrate.Considering the two simulations,the best device structure is PSS/ITO/NiO_x/Perovskite/TPBi/Ag.Then,PeLED devices with various structures in the above simulation are prepared,and their photoelectric properties are characterized.The electroluminescence(EL)intensity and EQE of NiO_x as HTL and PSS as substrate are the highest among various devices.Compared with the device with PEDOT:PSS as HTL and flat glass as substrate,the EQE at 5m A/cm~2 current density is increased by 82.6%.Next,in order to reduce the cost of device preparation under the condition of improved optical extraction efficiency,PDMS is used to transfer the surface microstructure of PSS to flat glass substrate device,and its EQE is also improved.Finally,in order to prove the reliability of the characterization results of the electroluminescent devices,samples for photoluminescence testing are prepared and tested.And the reliability of the above results is verified. |
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