Hydroxyethyl cellulose filled with M2+ chelate complexes with ethylenediaminetetraacetic acid (EDTA) as an effective electron-injection layer for polymer light-emitting diodes

Abstract

An effective electron-injection layer (EIL) is crucial to the development of highly efficient polymer light-emitting diodes (PLEDs) using stable, high work-function aluminium as the cathode. This work presents the first investigation using hydroxyethyl cellulose (HEC), filled with chelate complexes [(CH3COO)2-M, EDTA-M; M: Ca2+, Mg2+], as an electron-injection layer (EIL) to fabricate multilayer polymer light-emitting diodes (ITO/PEDO:PSS/HY-PPV/EIL/Al) by spin-coating processes. Devices based on HEC doped with EDTA-M provided the best performance. The maximum luminance and maximum current efficiency of polymer light-emitting diodes with EDTA-Ca in an HEC layer were 7502cd/m2 and 2.85cd/A, respectively, whereas those with EDTA-Mg were 8443cd/m2 and 3.12cd/A, which was approximately seven- to eight-fold of that without EIL. This performance enhancement was attributed to electron donation from the chelator that reduces metal cations to a “pseudo-metallic state”, enabling it to act as an intermediate step to facilitate electron injection. The results demonstrate that chelates of bivalent cations with EDTA can potentially serve as electron-injection materials for optoelectronic applications.