Influence Of CsCl On Organic Light-Emitting Devices Properties

Organic light emitting device is a electric field- driven device, in which light is from the organic layer, currently used in display and lighting area, and is considered the most promising lighting and display products in the 21 st century. OLED has many advantages, for example a low starting voltage, high contrast, all-solid state, active emitting, wide viewing angle, fast response, enabling flexible display, etc. But there are a lot of problems in the commercialization process, mainly for the device luminous efficiency is not high enough and the life can not meet the requirements of mainstream display products, etc. The fundamental reason is that the mobility of holes is two orders of magnitude greater than the mobility of electrons in the most organic materials, leading to a serious imbalance in the number of carriers reaching the light-emitting layer、the low composite rate and the low luminous efficiency, so the key to enhance luminous efficiency is a number of ways to balance the number of electrons and holes within the device. Currently, there are the following improving methods: modifying an anode to reduce the hole injection barrier, modifying an cathode to reduce the electron injection barrier, n-type doping in the subject material to increasing the mobility of electron in ETL(electron transport layer). Researchers have found that the majority materials suitable for the above improving methods is alkali metal compound. In this paper, Cs Cl is used for modifying and doping the device from following several ways, to study the impact on organic light emitting device performance:1. Preparing a normal device, the structure of which is ITO / NPB(50 nm) / Alq3(60 nm) / Al(120 nm), is a contrast device in the research process. Current、voltage、 brightness and other performance parameters of the device is measured to produce I-V, L-V and other characteristic curves, the results show that the starting voltage of the device is 3.7 V, the maximum brightness is only 1602 cd/m2, the maximum luminous efficiency is only 0.75 cd/A.2. New devices are prepared, the structure of which is ITO / NPB(50 nm) / Alq3(60 nm) / Cs Cl(0,0.2,0.6,1.0,1.4,1.8 nm) / Al(120 nm), and in which different thickness Cs Cl as the electron injecting material is added before the cathode of a normal device. The results show that the optimum thickness of Cs Cl is 0.6 nm and the performance of the device with the optimum thickness of Cs Cl is the best, of which the starting voltage is 2.5 V, the maximum brightness is 9223 cd/m2, about 5.75 times of the normal device, the maximum luminous efficiency is 3.87 cd/A, about 4.96 times of the normal device.3. New devices are prepared, the structure of which is ITO / NPB(50 nm) / Alq3(40 nm) / Alq3: Cs Cl(20 nm, 0,1,3,5,7,9% wt) / Al(120 nm), and in which different concentrations of Cs Cl is doped in ETL(electron transport layer) of the normal device. The results show that the optimum doping concentrations of Cs Cl is 3% and the starting voltage of the device with the optimum doping concentrations of Cs Cl is 3.0 V, the maximum brightness is 8723 cd/m2, about 5.45 times of the normal device, the maximum luminous efficiency is 2.34 cd/A.4. New devices are prepared, the structure of which is ITO / NPB(50 nm) / Alq3(40 nm) / Alq3: Cs Cl(20 nm, 0,1,3,5,7,9% wt) / Cs Cl(0.6 nm) / Al(120 nm), and in which Cs Cl is used as the electron injecting material and the dopant. The results show that the optimum doping concentrations of Cs Cl is 3% when the thickness of Cs Cl is 0.6 nm, and the starting voltage is 3.0 V, the maximum brightness is 9007 cd/m2. Comparing the optimal devices prepared in step 2、3 and 4, the device prepared in Step 2 is found to be the best.5. New devices are prepared, the structure of which is ITO / Cs Cl(0,0.1,0.4,0.7, 1.0,1.3 nm) / NPB(50 nm) / Alq3(60 nm) / Cs Cl(0.6 nm) / Al(120 nm), and in which Cs Cl is used as the hole blocking layer. The results show that the optimum thickness of Cs Cl is 0.4 nm, and the starting voltage of the device with the optimum thickness of Cs Cl is 2.9 V, the maximum brightness is 12410 cd/m2, about 7.75 times of the normal device, and the structure is the most optimal of all the devices prepared in the paper.