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Investigation on OLEDs efficiency roll-off with interfacial charge storage and their time-resolved emission spectra
摘要： Organic light-emitting diodes (OLEDs) are the next generation technique of display and lighting, confronted with the bottle-neck problem of OLEDs efficiency roll-off. The nature of luminescence and efficiency roll-off of OLEDs are processes of electrons and energy, during which charge injection and storage play important roles. In order to study the mechanism of OLEDs efficiency roll-off with interfacial charge storage, organic light-emitting devices with Ir(ppy)3 doped CBP as the light-emitting layer were prepared, and PMMA layers of 5 nm, 6 nm, 8 nm and 9 nm were inserted as charge storage layers to control hole injection and hole accumulation. The OLEDs efficiency roll-off is obvious with the increase of the current density. The storage of the interfacial charges is analyzed by transient electroluminescence measurement. Luminescence spikes occur at both forward and reverse turn-off voltages, which is caused by electron diffusion and trap carriers release, respectively. The time-resolved emission spectra prove the relationship of interfacial charges and exciton quenching. The OLEDs efficiency roll-off is positively correlated with the interfacial charge storage especially at low current density. This is due to the effect of the accumulation of the interfacial charge especially under unbalanced charge injection of OLEDs, which is of importance to improve the OLEDs performance and to decrease the OLEDs efficiency roll-off in industry.
关键词： OLEDs efficiency roll-off,Transient electroluminescence measurement,Interfacial accumulated charges
更新于2025-09-23 15:19:57
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The improved performance and mechanism of solution-processed blue PhOLEDs based on double electron transport layers
摘要： Performance improved solution-processed blue phosphorescent organic light emitting diodes (PhOLEDs) are demonstrated by adopting a double electron transport layer (ETL) strategy, which consists of TPBi and an additional Alq3 ETL. With the help of Alq3 ETL, the performance of the optimal device with a double ETL is significantly enhanced. The maximum luminance of OLEDs is improved from 6787 cd m?2 to 13 054 cd m?2, and the maximum current efficiency is increased from 3.9 cd A?1 to 11.4 cd A?1. Furthermore, the difference of carrier injection in the two types of PhOLEDs is explored by using the transient electroluminescence measurement method. The results imply that double ETL can help to balance electron injection and carrier transport, reduce the interface charge accumulation, leading to a high efficiency. The PL decay of the emission layer with different ETL is detected to analyze the effect of the introduced second ETL layer and the interface on the exciton decay of the emission layer. The results show that the introduced interface in devices with a double ETL has an adverse effect on the exciton emission, which contributes to the serious efficiency roll-off of devices with a double ETL.
关键词： blue PhOLEDs,performance improvement,solution-processed,double electron transport layers,transient electroluminescence measurement
更新于2025-09-19 17:13:59