ObjectiveIn the research of organic light-emitting devices (OLEDs), the spin mixing process is of great significance as it closely relates to device performance. In order to deeply investigate the effect of exciton concentration on the spin mixing process in organic light-emitting devices, the bulk heterojunction devices with the structure of ITO/MoO₃(5 nm)/NPB(30 nm)/NPB: Alq₃(1:x, 70 nm)/Alq₃(40 nm)/CsCl(0.6 nm)/Al(120 nm) [x=1, 2, 3, 4] are fabricated.MethodsThe optoelectronic properties and organic magnetic effects of the devices are studied at room temperature by utilizing the photo-electro-magnetic techniques. By applying these techniques, we can accurately obtain and analyze various parameters related to the devices' performance, such as current-voltage characteristics, light-emitting intensity under different magnetic fields, and the changes in these parameters with respect to different doping concentrations and bias voltages.Results and DiscussionsWe find that both the Magneto-Conductance (MC) and Magneto-Electroluminescence (MEL) curves of the devices are enhanced with increasing the doping concentration of Alq₃ under the same bias voltage at room temperature, among them increase by 1.4%. This indicates a strong correlation between the doping concentration and the performance metrics related to spin-dependent transport and light emission. Moreover, the amplitude of MC and MEL curves are reduced with increasing the bias voltage when the doping ratio remains unchanged. Additionally, the effect of temperature on the MEL curves of the devices is further investigated. The line-shape of the MEL curves are distinctly modulated with decreasing temperature, involving that the MEL curves within low magnetic field ranges increase rapidly, while that within high magnetic field ranges first increase slowly to decrease.ConclusionsThese experimental results are deeply analyzed by considering the intersystem crossing (ISC), triplet-triplet annihilation (TTA), and triplet-charge annihilation (TCA) mechanisms. We demonstrated that the exciton concentration can be effectively adjusted by modifying the doping ratio to further improve the optoelectronic properties and organic magnetic effects of the device. This work provides a reliable basis for designing the high-performance bulk heterojunction organic light-emitting devices by modulating the complex spin mixing process.