Numerical study of the influence of applied voltage on the current balance factor of single layer organic light-emitting diodes

摘要

Current balance factor (CBF) value, the ratio of the recombination current density and the total current density of a device, has an important function in fluorescence-based organic light-emitting diodes (OLEDs), as well as in the performance of the organic electrophosphorescent devices. This paper investigates the influence of the applied voltage of a device on the CBF value of single layer OLED based on the numerical model of a bipolar single layer OLED with organic layer trap free and without doping. Results show that the largest CBF value can be achieved when the electron injection barrier (Φ_n) is equal to the hole injection barrier (Φ_p) in the lower voltage region at any instance. The largest CBF in the higher voltage region can be achieved in the case of Φ_n ＞Φ_p under the condition of electron mobility (μ_(On)) ＞ hole mobility (μ_(Op)), whereas the result for the case of μ_(On) ＜ μ_(Op), is opposite. The largest CBF when μ_(On) = μ_(Op) can be achieved in the case of Φ_n = Φ_p in the entire region of the applied voltage. In addition, the CBF value of the device increases with increasing applied voltage. The results obtained in this paper can present an in-depth understanding of the OLED working mechanism and help in the future fabrication of high efficiency OLEDs.