We investigate the electron injection effect of inserting a thin aluminum(Al) layer into cesium carbonate(Cs2CO3)injection layer. Two groups of organic light-emitting devices(OLEDs) are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device's maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.
A white organic light emitting device(WOLED) combining the blue organic light emitting device with a red color conversion layer(CCL) is reported,which includes a fluorescent material N-(4-((E)-2-(6-((E)-4-(diphenylamino) styryl)naphtha len-2-yl)vinyl) phenyl)-N-phenylbenzenamine(N-BDAVBi) doped into 4,4'-N,N'-dicarbazole-biphenyl(CBP) as the blue light emitting layer,and the poly(2-methoxy-5-(2'-ethylhexoxy)-1,4-phenylene vinylene(MEH-PPV) as a red CCL.By optimizing the concentration of MEH-PPV in the CCL,a good white light emission is obtained,which shows that the stable CIE coordinates of(0.33,0.34) will have a slight change when the driving voltage is increased from 6 to 11 V.The maximum brightness and current efficiency of the optimized device are 11294 cd/m2 and 6.4 cd/A,respectively.
The metal-conducting single-walled carbon nanotubes(m-SWNTs)with small diameters(0.7 nm-1.1 nm)are selectively removed from the single-walled carbon nanotubes(SWNTs)by using HNO 3 /H 2 SO 4 mixed solution.Semiconducting single-walled carbon nanotubes(s-SWNTs)can be separated efficiently from the SWNTs with high controllability and purity based on this novel method,and the outcome is characterized by Raman spectrum.Moreover,the organic field effect transistors(OFETs)are fabricated based on the poly(3-hexylthiophene-2,5-diyl)(P3HT),and untreated SWNTs and separated SWNTs(s-SWNTs)are mixed with P3HT,respectively.It could be found that the P3HT/s-SWNT device exhibits a better field effect characteristic compared with the P3HT device.The current on/off ratio is increased by 4 times,the threshold voltage is also increased from-28 V to-22 V,and the mobility is increased from 3×10-3 cm2/Vs to 5×10-3 cm2/Vs.
To improve the performance of tandem organic light-emitting diodes(OLEDs), we study the novel NaCl as n-type dopant in Bphen:NaCl layer. By analyzing their relevant energy levels and carrier transporting characteristics, we discuss the mechanisms of the effective charge generation layer(CGL) of Bphen:NaCl(6 wt%)/MoO3. In addition, we use the Bphen:NaCl(20 wt%) layer as the electron injection layer(EIL) combining the CGL to further improve the performance of tandem device. For this tandem device, the maximal current efficiency of 9.32 cd/A and the maximal power efficiency of 1.93 lm/W are obtained, which are enhanced approximately by 2.1 and 1.1 times compared with those of the singleemissive-unit device respectively. We attribute this improvement to the increase of electron injection ability by introducing of Bphen:NaCl layer. Moreover, the CGL is almost completely transparent in the visible light region, which is also important to achieve an efficient tandem OLEDs.
We chose pentacene as a hole injection layer(HIL) to fabricate the high performance blue fluorescent organic lightemitting devices(OLEDs). We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120?C. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120?C annealed pentacene film and n-doped electron transport layer(ETL) presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.
