Manipulation of Emission Colors Based on Intrinsic and Extrinsic Magneto-Electroluminescence from Exciplex Organic Light-Emitting Diodes

Exciplex organic light-emitting diodes (XOLEDs) utilize nonemissive triplet excitons via a reverse intersystem crossing process of thermally activated delayed fluorescence. The small energy difference between the lowest singlet and triplet levels of exciplex also allows a magnetic field to manipulate their populations, thereby achieving ultralarge “intrinsic” magneto-electroluminescence (MEL) in XOLEDs. Here we incorporate it into a hybrid type of spintronic device (“hybrid spin-XOLED”), where the XOLED is connected to a magnetic tunnel junction with large magnetoresistance, to introduce an “extrinsic” MEL response that interferes with the “intrinsic” MEL. The ratio between two MEL contributions, the MEL value, and the field response were altered by changing the exciplex layer thickness or actively manipulated by adding another current source that drives the XOLED. Most importantly, by involving two XOLEDs (green and red) in the same circuit, the hybrid spin-XOLED shows a color change when sweeping the magnetic field, which provides an alternative way for future OLED display technologies

Electroabsorption Spectroscopy Studies of (C₄H₉NH₃)₂PbI₄ Organic–Inorganic Hybrid Perovskite Multiple Quantum Wells

Two-dimensional (2D) organic–inorganic hybrid perovskite multiple quantum wells that consist of multilayers of alternate organic and inorganic layers exhibit large exciton binding energies of order of 0.3 eV due to the dielectric confinement between the inorganic and organic layers. We have investigated the exciton characteristics of 2D butylammonium lead iodide, (C₄H₉NH₃)₂PbI₄ using photoluminescence and UV–vis absorption in the temperature range of 10 K to 300 K, and electroabsorption spectroscopy. The evolution of an additional absorption/emission at low temperature indicates that this compound undergoes a phase transition at ≈250 K. We found that the electroabsorption spectrum of each structural phase contains contributions from both quantum confined exciton Stark effect and Franz–Keldysh oscillation of the continuum band, from which we could determine more accurately the 1s exciton, continuum band edge, and the exciton binding energy