摘要
以富勒烯C60 作为空穴注入缓冲层 ,在结构为ITO/C60 /TPD/Alq3 /LiF/Al的器件中 ,改善了器件的发光效率。研究了C60 厚度对器件发光特性的影响。当C60 厚度为 1 6nm时 ,器件发光效率最高。在电流密度为 10 0mA/cm2 时 。
Organic electroluminescent devices using fullerene C 60 as a hole injecting buffer layer with different thickness have been prepared. The structure of the device is ITO/C 60 /TPD/Alq 3/LiF/Al (TPD: N,N′ diphenyl N,N′ bis(3 methylphenyl) 1,1′ biphenyl 4,4′ diamine, Alq 3:tris(8 quinolinolato) aluminum). The driven voltage are higher at the same current density with the increment of C 60 thickness. The driven voltages are 8 1V, 8 4V, 9 2V, 10 3V for the devices with 0nm, 1 2nm, 1 6nm and 2 0nm thickness of C 60 at the current density of 4mA/cm 2, respectively. The effects of the thickness of C 60 on the efficiencies of the devices are investigated. The device with 1 2nm C 60 buffer has the highest luminance while the current efficiency is not the optimum for this device,because the current density for this device is much greater than that for the device with 1 6nm C 60 buffer.The optimum thickness of C 60 buffer, 1 6nm, which produces the highest efficiency, is obtained. EL efficiency of the device, which contains 1 6nm C 60 buffer, has been improved by about a factor of one in comparison with the device without buffer at the current density of 100mA/cm 2. The undoped C 60 with high resistivity and first ionized potential using as a hole injecting buffer layer blocks the hole injection at the interface of anode and hole transporting layer. As the buffer becomes thicker, the current density is suppressed by decreased tunneling of holes under opplied voltage. As a result, the current densities are reduced at the same driven voltage. In the devices, Alq 3, which is an electron transporting and emissive layer, has a much higher electron mobility than hole mobility. Accordingly, in Alq 3, electrons are majority carriers and holes are minority carriers. In order to obtain high efficiency in organic electroluminescent devices the balanced electrons and holes injected from the cathode and anode into the emissive layer is required. Electroluminescence efficiency is controlled by the hole injection from the TPD into the Alq 3. Part of the driven voltage drops across the C 60 buffer, resulting in acceleration of injected holes and more accelerated holes injected into emissive layer. Thus, the reason for the improvement of efficiencies for the devices with suitable thickness of C 60 can be attributed to the more balanced carriers concentration in emissive layer.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2002年第3期269-272,共4页
Chinese Journal of Luminescence
基金
国家自然科学基金重大项目 (5 9790 0 5 0 )
国家自然科学基金资助项目 (696870 0 2
60 0 770 2 0 )
