Research On Doped Organic Optoelectronic Devices

Organic light-emitting diode (OLED) is becoming mainstream technology of green lightingand flat panel display. But there are still many problems to be solved, such as: lowing electroninjection, lowing intrinsic carrier concentration and lowing conductivity. The IBOLED can bebetter used in the AMOLED, However the capacity that electron from the indium tin oxide(ITO) injection to the organic functional layer and the transmission is weaker than conventionalOLED. Therefore improving the electron injection and transmission capability has becoming avital role for fabricating low-voltage, high efficiency OLED or IBOLED. In this letter, 3, 4, 9,10, perylenetetracarboxylic dianhydride (PTCDA) was be used as doping matrix, and Lithiumcarbonate (Li2CO₃) was be used as n-type dopant. PTCDA compared with traditional n-typematerials bathocuproin (BCP) and 4, 7-diphenyl-1, 10-phenanthroline (Bphen) has low prices,thermal stability and easily fabricated.In the research work, we found that Li2CO₃ will decompose into Li2O and O2 when it is inthe process of thermal evaporation under the ultra-high vacuum. Li2O can be reduced to Li andO2 by Al cathode in thermal evaporation, and Li atom can dope with PTCDA. We optimized thedoping concentration, and fabricated the bottom emission organic light-emitting devices usedthe eight hydroxyquinoline aluminum (8-quinolinolato aluminum, AlQ3) as the emitting layer.They have lower voltage, higher brightness and considerable efficiency than the device withLi2CO₃: BCP, LiF/Al.Based on indium tin oxide (ITO) as a transparent cathode and aluminum (Al) as the anode,we fabricate the inverted bottom-emission organic light emitting device that can be better fit tothe a-Si TFT drive-circuit. In this letter we use double n-type doped layer Li2CO₃: PTCDA/Li2CO₃: BCP as electron injection layer. The device Structure: ITO/Li2CO₃: PTCDA/Li2CO₃: BCP/AlQ3 /NPB/MoO₃/Al. Compared to the device that is used only doped layer Li2CO₃: BCP,it shows a lower voltage, higher brightness and power efficiency.We explore and study the stacked OLED. Two tacked devices are fabricated, one is usedLi2CO₃: BCP/MoO₃ as connection layers, and the other is used Li2CO₃: PTCDA/MoO₃ asconnection layers. By comparison, we found that Li2CO₃: BCP/MoO₃ was suitable forconnection layer in stacked OLED. On the basis of above, the single polar devices werefabricated that used Li2CO₃: BCP/MoO₃/MoO₃: NPB (x: 1) as charge generation layers.Comparing the different doping concentration, we find out the most doped concentration 2:1.