Addition of Lithium 8-Quinolate into Polyethylenimine Electron-Injection Layer in OLEDs: Not Only Reducing Driving Voltage but Also Improving Device Lifetime

作者：Chiba Takayuki; Pu Yong Jin; Ide Takahumi; Ohisa Satoru; Fukuda Hitoshi; Hikichi Tatsuya; Takashima Dai; Takahashi Tatsuya; Kawata So; Kido Junji

来源：ACS APPLIED MATERIALS %26 INTERFACES, 2017, 9(21): 18113-18119.

DOI：10.1021/acsami.7b02658

• zinc oxide
• lithium phenolate Complex
• polyethylenimine
• electron injection
• organic light-emitting device
• long lifetime

Solution-processed electron injection layers (EILs) comprising lithium 8-quinolate (Liq) and polyethylenimine ethoxylated (PEIE) are highly effective for enhancing electron injection from ZnO to organic layers and improving device lifetime in organic light-emitting devices (OLEDs). Doping of Liq into PEIE further reduces the work function of zinc oxide (ZnO) by enhancing dipole formation. The intermolecular interaction between Liq and PEIE was elucidated by UVvis absorption measurement and quantum chemical calculation. The OLEDs with ZnO covered with PEIE:Liq mixture exhibited lower driving voltage than that of the device without Liq. Furthermore, as doping concentration of Liq into PEIE increased, the device lifetime and voltage stability during constant current operation was successively improved.