Study On Transport Mechanism Of Hybrid Near-infrared Light Upconversion Sensors Based On OLED Light Display Unit

Hybrid near-infrared light upconversion sensor based on OLED light display unit is a photoelectric device,which can convert infrared light into visible light by coupling inorganic detection unit and organic display unit.Due to the massive demands and applications in military and civil fields,the devices have attracted extensive attention and continuous research by scholars at home and abroad.Although the performance has been greatly improved in recent decades,upconversion efficiency is still low so far.By studying the transport process of carriers in the device,the factors that affect the further improvement of the upconversion efficiency can be revealed,which has guiding significance for the practical application.In this paper,the transport mechanism of carriers is studied by means of temperature-dependent transient electroluminescence?EL?.First of all,the quantum-well?QW?OLEDs based on NPB/Alq₃ are fabricated in OMBD system.And the temperature-dependent I-V characteristic and the transient EL characteristic are analyzed in detail to explore the transport mechanism of carriers.It is found that the EL intensity varies with the transient duty-ratio in the QW OLEDs,whereas the bilayer NPB/Alq₃ device does not.In the single QW device,the superposition effect of carriers is the main transport mechanism,while the diffusion effect and space charge limited effect are the main transport mechanism in the multiple QW devices.It is different from the fall time remaining almost constant,the transient delay time increases linearly with the number of QW increasing,which is totally caused by the excitons'recombination position,that is Alq₃ well layer closed to the cathode.Secondly,the transport mechanism of carriers in hybrid near-infrared light upconversion sensors based OLED light display unit is studied in this paper.The influence factors of performance is analyzed by changing the near infrared?NIR?,bias voltage and temperature.The results show that the effect of NIR on luminance increases with the increasing of bias,and the influence is very small at low temperature.Once the temperature exceeds 200 K,the influence tends to be stable due to the space charge limited effect.When upconverter operates at low bias,the acceleration of luminance increasing with the raising of temperature increases first and then decreases gradually,and meets the maximum value when the temperature reaches 290 K.Due to the strong hole injection efficiency at high bias,the carriers break through the space charge limited effect,and the acceleration of luminance increasing with the raising of temperature increases.The analysis shows that the space charge limited effect and the thermionic emission effect are the main transport mechanisms under low bias.At high bias,thermionic emission is the main transport mechanism.Increasing temperature and applying NIR can decrease the delay time and prolong the fall time,and the effect of NIR is more obvious when the temperature is lower.