| Organic light-emitting diodes(OLEDs)have attracted extensive attention and continuous research from scholars at home and abroad due to their great application potential in the fields of lighting and display.Although OLED-based products have gradually entered people's lives,the further development of OLEDs is limited because of the low efficiency and high cost.The research on the mechanism of OLEDs can provide theoretical basis and guidance for improvement of device design and performance.Therefore,the injection,transport and recombination of carriers in OLEDs at different temperatures and the light-emitting mechanism were mainly studies by analysis of the transient variable temperature characteristics of OLEDs.Firstly,OLEDs based on BCP were fabricated by OMBD in this paper.The injection,transport and composite luminescence mechanism of carriers in devices were studied through the analysis of device's stable voltage characteristics and transient EL characteristics at different temperatures.It is found that the delay characteristics of OLEDs have temperature difference compensation effect(TDCE),and the factors affecting the delay time include minority carrier mobility and electron suppression traps in the device structure.The differences of compensation temperature caused by minority carrier mobility and electron suppression traps are 25 K and 20 K respectively.The results showed that the confinement effect of electron suppression traps on electrons is weakened at higher temperatures.By calculating the derivative(d N/d T)of N in devices,it is found that the inflection point temperature of devices is different,due to the imbalance between the injection rate and the transmission rate of electrons in devices.And it is found that the inflection point temperature difference of corresponding devices is consistent with the compensation temperature difference.Secondly,OLEDs with different structures were fabricated in this paper.The influence of hole injection barrier,electron mobility and exciton lifetime on the transient current response characteristics of OLEDs at different temperatures was studied.The results showed that hole injection barrier has a great influence on the device performance at lower temperature and the exciton lifetime has a great influence on the device performance when the temperature is higher.When the temperature is greater than 200 K,the injection rate of carriers in devices is increased by 1.5 times due to the reduction of the injection barrier.Theexciton number in phosphorescent OLEDs is 2.7 times more than that in fluorescent devices when temperature is more than 250 K.It is regarded that the exciton quenching rate in phosphorescent devices is balanced with the hole annihilation rate in fluorescent devices.In addition,threshold duty-ratio of devices decreases with the increase of temperature.It is suggested that the injection rate of devices increase with the rise of temperature,and more carriers are accumulated in the device when the same pulse voltage is applied to devices,so the device needs take a longer time to completely release these carriers.Therefore,its threshold duty-ratio will decrease with the increases of temperature. |
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