Effect of the Applied Bias Voltage on Exciton Profile and Efficiency Roll-Off in Organic Light Emitting Diodes

Despite organic light emitting diode (oled) devices reach more than 60% external quantum efficiency and in thermal activated delayed fluorescence (tadf) type ones, reach near 100%, efficiency roll-off in higher bias voltage due to the exction quenching and annihilation is unsolved. numerical simulation helps researchers to find fundamental parameters in excitonic profile of oled in higher bias voltage. in this paper, we present an electro-optical modeling of single layer phosphorescent oled to describe excitonic processes and loss mechanisims. we investigated electro-optical processes include radiative and non-radiative recombination of excitons, triplet-polaron quenching, triplet-triplet annihilation. simulation results show triplet-triplet annihilation at high bias increases due to the quadratic relation with exciton density and the contribution of triplet-polaron quenching decreases due to the larger effective electron mobility than the hole mobility at high bias voltage. the triplet-triplet annihilation process is the main reason for decreasing the radiation efficiency and efficiency roll-off at high bias voltage which is in good agreement with published experimental data. the results show how oled efficiency and radiative recombination of excitons decrease due to the roll-off process.

Effect of the applied bias voltage on exciton profile and efficiency roll-off in organic light emitting diodes

Despite organic light emitting diode (OLED) devices reach more than 60% external quantum efficiency and in thermal activated delayed fluorescence (TADF) type ones, reach near 100%, efficiency roll-off in higher bias voltage due to the exction quenching and annihilation is unsolved. Numerical simulation helps researchers to find fundamental parameters in excitonic profile of OLED in higher bias voltage. In this paper, we present an electro-optical modeling of single layer phosphorescent OLED to describe excitonic processes and loss mechanisims. We investigated electro-optical processes include radiative and non-radiative recombination of excitons, triplet-polaron quenching, triplet-triplet annihilation. Simulation results show triplet-triplet annihilation at high bias increases due to the quadratic relation with exciton density and the contribution of triplet-polaron quenching decreases due to the larger effective electron mobility than the hole mobility at high bias voltage. The triplet-triplet annihilation process is the main reason for decreasing the radiation efficiency and efficiency roll-off at high bias voltage which is in good agreement with published experimental data. The results show how OLED efficiency and radiative recombination of excitons decrease due to the roll-off process.