| Thermally activated delayed fluorescence (TADF) materials can take advantage of both singlet excitons and the singlet excitons which source from triplet excitons through up-conversion for light emission. TADF materials are promising candidates for next-generation solid-state lighting and full-color display source due to the internal quantum efficiency nearly 100%. Thus, design high efficiency TADF device is extremely urgent needs. Based on the idea of device design, doping concentration and thickness of EML, HIL, ETL, host and the device fabrication process of OLEDs about TADF materials have been studied in this thesis. In addition, for the purpose to ensure the interaction between host and guest, photophysical test and theoretical simulation have been done on the light-emitting layer. Based on the analysis and discussion of experimental data, we had got some conclusions:(1) The HOMO/LUMO of TXO-TPA and TXO-PHCZ are 5.37/3.49 eV and 5.78/3.58 eV, respectively. We can select mCP (HOMO/LUMO5.9/2.4 eV, ET= 2.9 eV) as their host due to a very low triplet energy level (2.13 eV,2.38 eV) and excellent thermal stability of TXO-TPA and TXO-PHCZ. Simultaneously, devices can be fabricated by vacuum deposition process. It has been demonstrated that PEDOT:PSS is more suitable for HIL, the best thickness and doped concentration of the EML are 35 nm and 5wt%, respectively. The maximum EQE of TXO-TPA and TXO-PHCZ devices are 18.5% and 21.5%, respectively.(2) Results have shown that TCTA (HOMO/LUMO= 5.7/2.7 eV, ET= 2.8 eV) is more suitable for TXO-TPA as a host. We combine the spin-coating with vaccum deposition method as device fabrication process for reducing the cost of fabricating device. In addition, we also investigated the effect of ETL of HOMO/LUMO energy level, electron mobility and triplet energy level on device performance. We found that the device which selected TPBI as ETL has an excellent performance. And the drive voltage, maximum current efficiency and EQE of device are 3.6V,16.2 cd/A and 5.97%, respectively.(3) The conclusions reveal that a ETL TPBI as a host of TXO-PHCZ has an excellent performance. Compared with HTL mCP, the maximum EQE of a ETL TPBI is 24.5% which increase by 14%. In order to explain the reasons for improving device performance fundamentally, we carry out a series of photophysical test of EML and Gaussian simulation to analysis the interactions between host and guest. We summarized a general method to select TADF host. As the host for TADF materials should satisfy the conditions:shallow LUMO, deep HOMO, high triplet energy level, emission peak has a larger overlap with absorption of guest, a big quantum yield after doped, a small AEst and a large radiative transition rate.(4) In fabricating device, ZnO nanoparticles based on modify by adenine as electron injection layer can increase the number of electrons in cathode. The standard inverted device has an excellent performance with the optimal thickness of adenine is 6 nm. The maximum current efficiency of standard inverted and standard device are 5.0 and 3.48 cd/A, respectively. |
PDF Full Text Request