Study On A New Kind Of Microcavity Polymer Light-emitting Diodes

Polymer light-emitting diodes(PLEDs)have attracted much attention due to their advantages of self light-emitting,light quality,small volume,wide viewing Angle,fast response speed,and easy processability,etc.Besides,PLEDs has huge potential applications for making ultra thin,large area,low driving voltage,bright color and flexible plat panel displays.Recently people have constantly developed new polymer electroluminescent materials and novel structure of polymer electroluminescent device to enhance device performances of the PLEDs.Based on the carrier injection theories of tunneling effect and space charge limited current(SCLC),the approprite electrode materials that matching energy levels of function layers and the introduce of carrier transport layer is very important.It is worth mentioning some special optical structure were applied to PLED recently,which can achieve high purity monochromatic light emission and luminous efficiency.Microcavity polymer light-emitting diodes(MPLEDs)has recently become a research hotspot because of its special optical model and excellent photoelectric properties.As MPLEDs can enhance the light emitting at certain wavelengths that correspond to allowed cavity modes,and achieve narrowed spectrum and enhance intensity of monochromatic emission.At first,we take the ITO/PEDOT:PSS/P-PPV/LiF/Al as a standard structure for a basic study.By researching on fluorene copolymer contains metal Pr or not,conclusion is PF(BipyPr)6 standard device has best luminescence performance,with the maximum brightness of 705cd/m2,and luminous efficiency of 1.53cd/A.And the CIE coordinates(0.24,0.41)is green light.By the research on standard devices,we found that thick layer can effectively reduce the leakage current and improve the luminous efficiency of devices.And 80 ? annealing can improve the crystallinity of emitting layer,which can can increase the film defects when the luminous layer is thin,leading to device leakage current increase obviously.We design and fabric microcavity PLEDs with a device structure of Ag(80 nm)/ZnO/PEI/P-PPV/MoO3/Ag(15 nm)to narrow the emission spectra of P-PPV.The double metal films were used both as the electrodes and mirrors of the microcavity,which simplified the device structure effectively.Moreover,the resulting top-emission devices are desirable for active matrix PLED display.Solution processed ZnO film serves as ETL,branched polycthylenimine(PEI)film formed from the dilute PEI solution is used both as electron injection layer and hole blocking layer.Compared with the conventional device(ITO/PEDOT:PSS/P-PPV/LiF/Al)and inverted device(ITO/ZnO/P-PPV/MoO3/Ag),The MPLEDs showed excellent color saturation and high luminous efficiency.The device performances of microcavity device are effected by carrier transmission,location of exciton compound and microcavity resonant mode(the cavity length)and other factors together.Hence,by controlling exiton reombination position and altering electrode materials,the MPLEDs are optimized.We introduced PEI as the interface modification layer of cathode,for reducing the barrier of electronic transfer to the light-emitting layer and regulate hole migration in the device,to balance the carrier transfer.At last,by optimizing the thickness of PEI and P-PPV,the best device achieved a maximum brightness of 14220 cd/m2 and a highest luminous efficiency of 11.35 cd/A with CIE color coordinates of(0.24,0.70).Besides,with semi-transparent Al anode,the devices showed better color saturation with CIEcolor coordinates(0.19,0.71).Both are located in the region of pure green light.