Investigating the effect of the conductivity of the electron transportation layer on the organic light-emitting diodes

Abstract

In this paper, we choose three types of n-doped electron transport layer (ETL) materials with different chemical structures to fabricate only-electron carrier device for studying the conductivity of them, namely, 100 nm ETL1, 40 nm ETL2, and 23 nm ETL3. It is also analyzed that the effect of the potential barrier height on the carrier injection efficiency of the single-carrier device when they directly contact with the electrode having the different work function ITO (indium tin oxide film) electrode. When the thickness of the organic electron transport layer is thin, the current density is mainly limited by the injection barrier in the interface, However, When the thickness of the organic electron transport layer is thick, the organic electron transport layer with very low carrier mobility is a dominant factor in limiting the current through the device. If ETL1 is in contact with a lower work function aluminum electrode relative to the ITO electrode, the effect of the injection limit on the current is weaker. Considering Poole-Frenkel effect and space charge limited current effect, the field strength-dependent carrier mobility of ETL1 material is estimated by linear-fitting the current-electric field characteristic curve of only-electron device. Organic red light-emitting diode is fabricated with ETL1 thicknesses of 10 nm and 100 nm, respectively. For the organic light-emitting device with 100 nm ETL1, it reaches 14.9 cd/A at a current density of 30 mA/cm2 , and the color coordinates is (0.658, 0.341).