Charge generation layer with Yb assistant interlayer for tandem organic light-emitting diodes

Tandem organic light-emitting diode (OLED) devices require an efficient charge generation layer (CGL) between two stacked OLED units. In this study, a CGL with an Yb assistant interlayer was fabricated and investigated. The optical transmittance and charge generation performances of the CGLs were analyzed with respect to the Yb thickness. The best result was obtained at a Yb thickness of 3 nm, at which both the electrical and optical properties exhibited optimal performances. The optical transmittance was greater than 90 %; this was superior to the performances using Ag and Al interlayers. The insertion of a 3-nm Yb layer reduced the threshold voltage from 18 to 6 V. Capacitance measurements revealed that the insertion of the Yb layer enhanced charge generation in the CGLs, reducing the threshold voltage and enhancing charge transport. The tandem OLED device fabricated using Bphen:Liq/Yb/MoO3/TAPC as a CGL exhibited a 1.92 x enhancement in the current efficiency, which is nearly twice the ideal value, compared to a single-unit device. Thus, Yb is a promising candidate for use as an assistant interlayer in CGLs for high-performance tandem OLED devices.