Research On Transition Metal Nitride Anode Structure With High Work Function In Organic Light-Emitting Diodes

Organic light-emitting diodes(OLED)are of growing interest in lighting,display,and biomedical fields because of their active lighting,low power and gently weight.Anode materials with high work function,excellent optical and electrical properties are crucial for realizing high-performance OLED devices.However,the poor hole-injection property of conventional transparent conductive anodes and highly reflective metal anodes severely hinders the realization of high-performance OLED devices.Here,this dissertation is aimed at the realization of high-performance OLED devices,mainly focusing on the preparation of high work function transition metal nitride films,and the enhancement of hole-injection efficiency of anodes and performance of OLED devices.The main research contents and results of the dissertation are as follows:1.The work function and surface energy of titanium nitride(TiNx)and molybdenum nitride(MoNx)were calculated based on the first principle,and the results provide technical guidance for the preparation of high work function TiNx films and MoNx films.The calculation results show that the work functions of(111-N)plane in the face-centered cubic TiNx phase and face-centered cubic MoNx phase and(001-N)plane in the hexagonal MoNx phase are higher than 5.0 eV,which indicates that the face-centered cubic TiNx films and the face-centered cubic MoNx films with preferred orientation perpendicular to the(111-N)plane and the hexagonal MoNx films with perpendicular to the(001-N)plane have the potential to improve the hole-injection efficiency of traditional anodes used in OLED devices.2.Based on the theoretical calculation of different crystal planes of the face-centered TiNx phase,we have carried out the preparation of the high work function TiNx films by pulsed laser deposition.The results show that the adsorbed atoms on the surface of the TiNx films could affect the work function of the TiNx films.The C atoms could slightly reduce the work function of the TiNx films,and the O atoms will could greatly improve the work function of the TiNx films.The work function of the TiNx films is also affected by the atomic ratio of N/Ti,and its work function will increase with the increase of the atomic ratio of N/Ti.3.The Al/TiNx anode structure has been successfully fabricated for improving hole-injection efficiency in top-emitting OLEDs(TOLEDs)by magnetron sputtering and pulsed laser deposition.The device performance results show the TOLEDs with Al/TiNx has lower driving voltage at the same current density.For instance,the driving voltages of the TOLEDs with Al/TiNx and Al anode are 3.4 V and 7.5 V at 20 mA/cm2,respectively.And the brightness of the TOLEDs with Al/TiNx are much higher than that of the TOLEDs with Al anode at the same driving voltage.For instance,the brightness of the TOLEDs with Al/TiNx and Al anode is 10000 cd/m2 and 400 cd/m2 at 3.3 V,respectively.4.Based on the theoretical calculation of different crystal planes of the face-centered MoNx phase and the hexagonal MoNx phase,we have carried out the preparation of the high work function MoNx films.The MoNx films were successfully prepared by magnetron sputtering on different substrates at different sputtering powers.The effect of crystal structure on work function of MoNx was systematically studied.The results show that high work functions exceeding 4.85 eV and a lower resistivity of the order of 10-4Ω·cm have been obtained in the MoNx films with different crystal structures.These properties make the MoNx film a promising modification layer for enhancing the hole-injection of anodes used in OLED devices.5.The ITO/MoNx anode structure and the Al/MoNx anode structure have been successfully fabricated by magnetron sputtering for enhancing the hole-injection efficiency of OLED devices.The device performance results show that the MoNx layer can effectively improve the efficiency of hole-injection from ITO or Al layer into the organic layer.The effect of the growth time of the MoNx layer on the performance of the TOLED device was also studied.The results show that the TOLED with Al/MoNx(6 s,3.7 nm)exhibits low driving voltage and high brightness and high efficiency at the same time.