| 초록 |
We introduce two air-stable polymer interlayers (ILs), branched polyethyleneimine (PEI) and polyethyleneimine ethoxylated (PEIE) for use in inverted polymer light-emitting diodes (IPLEDs), and compare these with Cs2CO3 ILs. These polymer ILs can reduce the electron injection barrier between ZnO and emitting layer by decreasing the work function (WF) of underlying ZnO, thereby effectively facilitating electron injection into the emitting layer. We also study that WF of ZnO covered by PEI is lower than that covered by PEIE due to higher [N+]/[C] ratio of PEI. Furthermore, because polymer ILs have an insulating property, they can block the quenching of excitons and increase the luminous efficiency of devices. Thus, IPLEDs with PEI ILs of optimum thickness (8 nm) show current efficiency (13.5 cd A-1) and power efficiency (4.98 lm W-1), which are dramatically higher than those of IPLEDs with Cs2CO3 ILs (8 cd A-1 and 1.93 lm W-1). |
