Study About Increasing The Efficiency Of Carrier Injection And Transport In OLED And The Performances Of Devices

In resent years, organic light emitting devices (OLED) display and lighting as a novel technology will experience the revolution of technology about display and lighting due to its excellent advantage of self-light emitting, wide color gamut, soft lighting color, wide viewing angle(>175°), fast response time(<1μs), thin panel(<1 mm), low driving voltage(3¹0 V), high efficiency and environment protection, realize the produce of large size, flexible, and double sided or transparent display, etc. At the present time, the application field for display and lighting about OLED is developing rapidly. The study about lowering operating voltage, increasing efficiency, and simplifying fabrication process for OLEDs must be developed for accomplishing its widespread applications on excellent performances of blue light emission and combining with down-convert layers for white light emission. Therefore, our works are mainly focus on increasing the efficiency of carrier injection and transport in OLED and the performances of devices, and some achievements in research are attained. The main results of the article include three aspects as below:1. Study about improving the performances of OLED by increasing the efficiency of hole injection and transport in OLED. The efficiency of hole injection and transport in OLED is increased utilizing the electron acceptor F4-TCNQ used as anode buffer layer and p-type dopant, respectively, and improving the performances of OLED accordingly. The optimum Alq3-based OLED with F4-TCNQ buffer layer exhibit a lower turn-on voltage of 2.6 V, a higher brightness of 39820 cd/m² at 13 V, and a higher current efficiency of 5.96 cd/A at 6 V, which is 1.9 times higher than that of the optimum p-doped devices (3.11 cd/A at 7 V), and nearly 2.2 times higher than that of the conventional devices (2.74 cd/A at 10 V), respectively. These results indicate that the EL performances of OLED could be effectively improved by inserting a thin F4-TCNQ film as the anode buffer layer between the anode ITO and HTLβ-NPB, and the fabrication process is simplified. At the same time, the corresponding physical mechanisms are analysed.2. Study about improving the performances of OLED by increasing the efficiency of electron injection and transport in OLED. The high electron injection and transport ability, high brighness, and high efficiency CBP: NBDAVBi-based blue OLED is fabricated successfully, which is utilizing the Cs-derivatives, including Cs₂CO₃ and CH₃COOCs, as the n-dopant doped into a novel electron transporting material NBPhen for producing an efficient effect of n-doping. The optimum devices with Cs₂CO₃-doped and CH₃COOCs-doped exhibit the current density of 551.80 mA/cm² and 527.88 mA/cm² at 14 V, the corresponding brightness of 39750 cd/m² and 39820 cd/m² at 14 V, and the current efficiency of 14.60 cd/A and 14.50 cd/A at 10000 cd/m², respectively, which are obviously superior to those of the conventional devices (312.39 mA/cm² and 25190 cd/m² at 14V, and 9.45 cd/A at 10000 cd/m²). These results obviously revealed that introducing the n-ETL NBphen: Cs-derivatives in OLED not only efficiently reduces the electron injection barrier, but also powerfully increases the carrier density for current conduction in n-ETL, which results in a higher efficiency for OLED. At the same time, the experiment results indicate that CH₃COOCs with lower deposition temperature could replace the used n-type material Cs₂CO₃ as n-dopant.3. Study about improving the performances of devices by increasing the efficiency of carrer injection and transport in OLED. The simple structure and high performances blue OLED is fabricated, which is consisted of F4-TCNQ as anode buffer layer, CH₃COOCs as n-dopant, and a novel blue fluorescence material TC-1759 as non-doped bule emitting layer(B-EML). The optimum device exhibit a lower turn-on voltage of 2.2 V, a higher brightness of 16351 cd/m² at 10 V, and the maximum current efficiency of 10.42 cd/A, which is 2.2 times higher than that of the conventional devices (4.75 cd/A). The corresponding physical mechanisms are further analysed. These results indicate that the non-doped TC-1759 as B-EML not only could accomplish excellent performances of blue light emission but also be used as excited source for down-convert layers for white light emission, which may satisfy the request of commercial application.