Analysis of Color Shift Mechanism for Organic Light Emitting Diode Doped with a Green Emitter

Abstract

The electro-optical characteristics of OLEDs have been investigated through numerical simulation. Stationary, multi-layer (ITO/NPB/Alq3:C545T/ Alq <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }_{3} /$</tex> LiF) devices containing C545T fluorine as a dopant throughout a range of different concentrations have been created to investigate colorimetric and energy transfer behavior. The chromatic coordinates of the resulting devices were evaluated using the CIE 1931 color space. The major finding was that increasing the C545T dopant concentration led to a significantly longer wavelength of emission and a higher contribution of the dopant to the luminescence. The shifts observed in the electro-luminescence spectrum were mirrored in the chromatic coordinates within the CIE 1931 color space. Increasing the concentration of the dopant leads to a decrease of the luminance and efficiency due to concentration quenching mechanisms. The analysis of both electrical and optical properties further revealed that energy transfer between the host and dopant is the principal physical mechanism controlling color modulation; whilst also demonstrating that there is a trade-off between emission efficiency and chromatic stability at high dopant concentrations. The proposed simulation framework constitutes a robust platform for the optimization of OLED design and is particularly well suited to an extension towards the integration of parameter optimization algorithms as well as the study of chromatic stability under constraints, opening the way to the development of reliable and color-stable OLED devices for advanced display and lighting applications.