Effect of NaCl doped into Bphen layer on the performance of tandem organic light-emitting diodes

To improve the performance of tandem organic light-emitting diodes (OLEDs), we study the novel NaCl as n-type dopant in Bphen:NaCl layer. By analyzing their relevant energy levels and carrier transporting characteristics, we discuss the mechanisms of the effective charge generation layer (CGL) of Bphen:NaCl (6 wt%)/MoO₃. In addition, we use the Bphen:NaCl (20 wt%) layer as the electron injection layer (EIL) combining the CGL to further improve the performance of tandem device. For this tandem device, the maximal current efficiency of 9.32 cd/A and the maximal power efficiency of 1.93 lm/W are obtained, which are enhanced approximately by 2.1 and 1.1 times compared with those of the single-emissive-unit device respectively. We attribute this improvement to the increase of electron injection ability by introducing of Bphen:NaCl layer. Moreover, the CGL is almost completely transparent in the visible light region, which is also important to achieve an efficient tandem OLEDs.