Fabrication And Properties Of Inorganic Copper Thiocyanate/copper Iodide Composite As A Hole Transport Layer

Solution-processed polymer light emitting diode(PLED)not only can reduce costs and realize large areas but also have the potential to realize fast manufacture by roll-to-roll processing.Hole transport layer(HTL)as the interface between anode and light emitting layer,which is the fundamental of the device.Poly(3,4-ethylenedioxythiophene): poly(styre-neesulfonate)(PEDOT:PSS)is the most extensively used hole transport material in PLED.However,it's acidic(PH<2)and hygroscopic nature will decrease devices efficiency and stability in long-term operation.Therefore,it's necessary to find a hole transport material with high performance and good stability.Copper thiocyanate(?-CuSCN)and copper iodide(?-CuI)are inorganic P-type semiconductor materials.The highest occupied molecular orbital(HOMO)of ?-CuSCN is 5.5eV and its mobility is 0.01~0.1cm2/(V?s)and solution-processed film has a smooth morphology with about 1.4nm roughness.The HOMO of ?-CuI is 5.1eV and its mobility is 0.5~0.2 cm2/(V?s)and solution-processed film has a rough morphology with about 12.3nm roughness.Therefore,combine CuSCN and CuI which can achieve a inorganic composite hole transport material with low HOMO energy,high mobility and smooth morphology.In this paper,we concentrate on preparation the composite materials,analysis the performance of the composite films and their application in PLEDs,and the following works were done:(1)CuSCN and CuI are dissolved in diethyl sulphide(DES)respectively.Mixing the two solutions and format different CuI mass fraction in CuSCN/CuI composite materials.The ultrasonic bath also given to make sure the composite materials mixed well.The composite solutions are annealed to achieve solid composite materials and the materials crystal structure was characterized.(2)The CuSCN/CuI composite with different CuI mass fraction obtained by spin coating and the influences of Cu I mass fraction to the films surface topography,roughness and transmittance in visible light also be investigated.(3)Investigated CuSCN/CuI composite materials transport properties by hole only devices: ITO/CuSCN:CuI/SY/MoO3/Ag and the effect of CuI mass fraction in composite materials have been analyzed.(4)PLEDs with the structure:ITO/CuSCN:CuI/SY/LiF/Al were fabricated and tested and the devices electroluminescence spectra,current density-voltage,luminance-voltage,repeatability and stability.The devices show better luminances and current efficiencies than PEDOT:PSS-based PLED when CuI mass fraction is no more than 50% in composite materials.