Improving The Performance Of Organic Light-emitting Diodes

Organic Light-Emitting Devices?OLED?have attracted considerable interest in the field of display and solid-state lighting,because of their advantages of low driving voltage,high brightness,and wide perspective.An increase number of researchers are devoted themselves to exploring this study that has achieved so many significant achievements that promote the industrialization development of OLED.However,it still faces challenges on commercial application that include balance of the carrier injection and transport,simplify of the device structure and stability of the spectral are unsolved.To solve these problems,we performed the study of the highly efficiency and stability OLED.?1?Utilizing the Sol-gel method to prepare the Cu O_x thin film and introducing Cu O_x/poly?3,4-ethylenedioxythiophene?poly?styrenesulfonate??PEDOT:PSS?bilayer as hole injection layers?HILs?to modify the device anode interface,we investigated the different hole injection materials on the performance of phosphorescent OLED?Ph OLED?.It was clearly found that the utilization of Cu O_x/PEDOT:PSS as hole injection layers?HILs?not only enhances the balance of the electron and hole,but also reduces the efficiency roll-off significantly.In summary,we obtained an efficient blue phosphorescent OLED?Ph OLED?devices,the maximum luminance and current efficiency of the device reach 17180 cd·m^-2 and 28.6 cd·A^-1,respectively.?2?The nondoped emitting layer?EML?was constructed by introducing a ultrathin layer of pure green phosphorescent dye tris?2-phenylpyridine?iridium[Ir?ppy?₃]between a hole transporting layer TCTA and an electron transporting layer TPBi.The device structure is ITO/Mo O₃?2nm?/NPB?40 nm?/TCTA?10 nm?/Ir?ppy?₃?0.1⁰.5 nm?/TPBi?40 nm?/Li F?1 nm?/Al?80 nm?.The thickness of EML can affect the performance of green Ph OLEDs.By changing the thickness of emitting layer,we found that the best performance of green Ph OLED can be achieved with a 0.2 nm pure phosphorescent dye layer.The device exhibited highly efficient green emissiona with a maximum luminance of 26350 cd·m^-2,a maximum current efficiency of 42.9 cd·A^-1and a maximum external quantum efficiency of 12.92%.These results indicated that high performance Ph OLED can be realized with only ultrathin nondoped EMLs in a simple way.?3?Stable pure-blue electroluminescence?EL?is obtained from polymer light-emitting devices by dispersing poly?9,9-dioctylfluorene??PFO?into a wide band-gap mixed-matrix of poly?9-vinylcarbazole??PVK?:2-?4-biphenylyl?-5-?4-tert-butylphenyl?-1,3,4-oxadiazole?PBD?.From the EL spectra of the PFO doped films,we find that the additional green emission observed in the EL spectra of pure PFO devices was significantly suppressed in the PFO doped devices.The spectral stability was also improved through evaluating the EL spectra of the PFO doped films annealed at different temperatures?from 80 to 150??.These results demonstrate that doping of PFO into a matrix to weaken the aggregate and oxidation of the PFO molecules is a simple strategy to suppress the green emission.