Property change of organic light-emitting diodes using a TCNQ

TCNQ를 사용한 유기 발광 소자의 특성 변화

We have studied physical properties of organic light-emitting diodes (OLEDs) in a device with 7,7,8,8-tetracyanoquinodimethane (TCNQ). Since the TCNQ has a high electron affinity, it is widely used for a charge-transport and injection layer. And the TCNQ-derivatives have also been used to control the conductivity of the materials. It is known that a charge injection and transport in OLEDs with a TCNQ-derivative enhances a performance of the devices such as operating voltage and efficiency. To see how the TCNQ affects on the device performance, we have made a reference device in a structure of ITO(170nm)/TPD(40nm)/$Alq_3$(60nm)/LiF(0.5nm)/Al(100nm). And several type of devices were manufactured by doping TCNQ either in TPD or $Alq_3$ layer. The TCNQ layer was also formed in between the organic layers. N,N'-diphenyl-N,N'-di(m-tolyl)-benzidine (TPD), tri(8-hydroxy quinoline) aluminium ($Alq_3$), and TCNQ layers were formed by thermal evaporation at a pressure of $10^{-6}$ torr. The deposition rate was $1.0{\sim}1.5\;{\AA}/s$ for TPD, and $1.0{\sim}1.5\;{\AA}$ for $Alq_3$. The LiF was thermally evaporated at a deposition rate of $0.2\;{\AA}/s$ successively. The device with TCNQ-derivative improved the turn-on voltage compared to the one without TCNQ-derivative.