Research On Color-tunable Organic Electroluminescent Device

As a mature technology,organic light-emitting diodes（OLEDs）have a promising potential for the next generation of displays and lighting.In recent years,the tunability of solid-state light sources has become a desirable feature for the lighting and display industry.Intelligent lighting systems that can meet consumer demands,such as real-time color adjustment in response to environmental changes,are rapidly developing.The ability to independently control the spectrum and intensity of the light source is thus crucial in intelligent lighting systems.This paper presents the feasibility of color-tunable OLED devices that can serve as light sources for smart lighting systems.The devices are composed of forward and inverted sub-cells.Compared to the traditionally studied wide color gamut OLEDs composed of homostructured sub-cells,the designed devices have the capability to meet the structural requirements of different materials,resulting in high efficiency and high luminance light emission.The main work done in this paper is as follows:（1）Two structures are proposed for achieving color-tunable organic electroluminescent devices,a vertical structure and a planar structure,allowing the combination of forward and inverted subunits in the same set of circuits.For the device performance,Mo O₃ was chosen as the anode modification layer.The effect of Mo O₃ thickness variation on device performance was investigated to determine the most suitable thickness for this study.Zn O/PEI was introduced as an electron transport layer to solve the problem of electron injection into the inverted structure.The low surface roughness of Zn O/PEI allows for stable contact with the light-emitting layer;the light transmission of approximately 90%allows for higher luminous brightness.The successful luminescence of the two devices demonstrates the practicability of the proposed structure.Considering the operability of the devices,a color-tunable organic electroluminescent device with a planar electrode structure was chosen for the study,and the structure of the device was determined.（2）The working mechanism of a single-emission color-tunable device is discussed,illustrating the superiority of the new structure designed compared to conventional OLEDs.The green light was chosen for the study of single emitter color tuning to highlight the universality of the designed structure.An alternating current（AC）signal is used to drive the device,and the AC signal addresses each emitter unit independently to achieve independent controllability of the emission intensity and spectrum of the subunit.When the AC signal is applied to drive,charge accumulation is avoided due to the constant reversal of the external electric field.Moreover,the frequency of the AC power supply and the amplitude of the AC signal are explored in detail to control the OLED in terms of color temperature and intensity.（3）A study of multi-emission color-tunable organic electroluminescent devices was carried out,in which planar-structured OLEDs composed of fluorescent blue and polymer yellow light-emitting subunits were prepared utilising complementary colors.By comparing the optoelectronic properties,a planar structure composed of a forward blue subunit and an inverted yellow subunit was applied to the study.The mechanism of color tuning is discussed in depth.The effects of AC frequency,pulse amplitude,and amplitude ratio on the emitted color tuning under AC drive are illustrated separately.The design of the planar structure makes white OLEDs easy to implement,and the devices can transition from blue to white and then to yellow light.It is shown that a functional structure with an orthogonal and inverted integrated AC drive allows for color tuning that can be integrated into commercial power systems to adapt to various lighting situations and has potential for future development in the field of intelligent lighting.