| Since its commercialization,Organic Light Emitting Devices（OLEDs）have rapidly captured the market share of Liquid Crystal Display（LCD）in both large and small size display panels.They are widely used in intelligent terminal displays in the era of the Internet of Things,and are expected to become the next generation of lighting technology.Based on its huge application prospects,researchers have proposed a series of innovative research strategies,developed a large number of new materials and designed different device structures,which can improve exciton utilization while reducing losses in the optical output process.One of the key points is to reduce the generation of internal leakage current（usually caused by the imbalance of internal electron and hole transport,and most carriers are transported to another electrode）in the device,thereby achieving the goal of improving device efficiency and enhancing stability.This article mainly focuses on a series of structural optimization for red light OLEDs to improve device performance.The research content is mainly divided into the following two parts:（1）The indium tin oxide（ITO）electrode was modified with 3-aminophenylboronic acid（3ABBA）.The boric acid group of 3ABBA undergoes a protonation reaction with the hydroxyl group on the ITO surface to form a bond.Therefore,3ABBA molecules are tightly stacked on the ITO surface,forming a smooth and flat self-assembled monolayer（SAM）.After characterizing the thin film using ultraviolet photoelectron spectroscopy（UPS）and calculating,it was found that the introduction of 3ABBA-SAM reduced the energy level difference with TAPC,allowing hole carriers to enter the device interior only by overcoming small potential barriers.Through systematic characterization of SAM by means of XPS,water contact angle,AFM,etc.,it was found that the hydrophilicity of SAM formed after 3ABBA modification was significantly reduced,improving the stability of the device under unpackaged conditions.At the same time,it was found that when the concentration of3ABBA was low,a dense film could not be formed on the ITO surface,leading to the formation of pinhole defects;When the concentration is high,molecular overlap will also occur,increasing the surface roughness.The experimental results show that when the concentration is 0.03 mol/L,the surface roughness of SAM is good,the external quantum efficiency（EQE）of the prepared red OLED is 15.40%,the current efficiency（CE）is 10.26 cd A-1,and the power efficiency（PE）is 8.52 lm W-1,all of which have better performance than devices based on PEDOT:PSS.（2）The hole transfer rate in OLED devices is generally two orders of magnitude of electrons,breaking the charge transfer balance.We use polymethyl methacrylate（PMMA）to insert between ITO and the hole transport layer to regulate the transport of hole carriers within the device and the recombination region with electrons.At the same time,we use the bipolar material DTBDQ as the main material of red light OLED devices,which acts together with the PMMA buffer layer to limit the recombination region of carriers.Although PMMA itself does not have electrical conductivity,under sustained voltage,holes are injected into the device through tunneling effects,which balances carrier injection and improves device luminous efficiency by reducing the current density of the device.We prepared buffer layers formed by different concentrations of PMMA solutions on ITO using a wet process method,and then tested the performance of the device.The data results showed that when the PMMA concentration was 0.65 mg/m L,the OLED device achieved the optimal balance of carriers,enhanced the effective radiation recombination of carriers,and achieved device EQE of 19.45%,CE of 14.13 cd A-1,and PE of 12.59 lm W-1. |
