Application of [Pt(II)(tetra-tert-butylSalophen)] complex within organic devices: Deep red emission, bistable light-emitting diodes and operational stability

Abstract

This paper focuses on the Negative Differential Resistance (NDR) we observed on organic light-emitting diodes (OLEDs) using [Pt(II)(tetra-tert-butylSalophen)] as host, since this Pt(II) complex displays a deep-red emission (λmax = 660 nm). Electrical characterizations of monolayer devices have shown that doping Tris-(8-hydroxyquinoline)aluminum (Alq3) as matrix emissive layer with this complex, leads to the modulation of the charge transport properties highlighted by Negative Differential Resistance (NDR). Upon electrical driving stresses, the conductivity of active layer can be switched between two electrical states (ON and OFF) with a figure of merit higher than 103. By adding an electron-blocking layer, we demonstrated that the NDR trend is closely related to negative charge accumulation within Alq3 leading to the modification of electronic properties in the vicinity of anode/active layer interface. The NDR phenomenon is interpreted in terms of space charge polarization (SCP) linked to charge trapping/untrapping mechanism as a consequence of the polarization/depolarization of the Pt(II) complex. Under electrical driving stresses, the performance of the devices which include the Pt(II) complex, are stabilized. A schematic model is proposed to depict the SCP responsible for NDR and decrease-resetting behaviors observed in these devices.