The Influence of Energy Transfer on the Color Temperature Change in Color-Tunable Organic Light Emitting Diodes with Interface Exciplex

The color-tunable white organic light-emitting diode (CT-WOLED) with wide correlation color temperature (CCT) has many advantages in optimizing the artificial light source to adapt to the human physiological cycle. The research on the change trend of CCT and the law of extending the change range of CCT will help to further improve the performance of this kind of device. The present work fabricated a series of CT-WOLED devices with a simple structure, which are all composed of two ultra-thin phosphor layers (PO-01 and Flrpic) and a spacer interlayer. The yellow interface exciplex (TCTA/PO-T2T) formed between the spacer layer (PO-T2T) and transmission material (TCTA) in EML will decrease the CCT value at low voltage. The relationship between the energy transfer in EML and CCT change trend is investigated by adjusting the interface exciplexes and the thickness of the interlayer or the phosphor layer in devices A, B and C, respectively. The results demonstrate that a simple OLED device with an interlayer inserted between two ultra-thin phosphor layers can achieve a wider CCT span from 3359 K to 6451 K at voltage increases from 2.75 V to 8.25 V. .

Efficient red phosphorescent OLEDs based on the energy transfer from interface exciplex: the critical role of constituting molecules

A novel acceptor material,9-(4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)-9H-carbazole(o-DTPPC)was developed to form interface exciplex with commonly used donors,to maximize the performances of red phosphorescent organic light emitting diodes(PHOLEDs).It is found that the exciplex involving 4,4′-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline)(TAPC)exhibits the most significant thermally activated delayed fluorescence(TADF)property,derived from the high triplet energy level as well as strong hole-transporting ability of TAPC.Intriguingly,it is the same donor-acceptor combination which achieved the highest device efficiency when adopted as the host for red PHOLEDs.Maximum efficiencies as high as31.36 cd A^(-1),17.95 lm W^(-1),and 21.01%for the current efficiency,power efficiency and external quantum efficiency,respectively with low efficiency roll-off were realized.The improved performance can be attributed to the efficient TADF properties of the interface exciplex-forming host constituting TAPC,benefiting the F?rster energy transfer.The article first underlines the importance of the constituting molecules in the interface exciplex-forming hosts,shedding new insight about the choice of interface exciplex as the host for PHOLEDs,which may lead to even higher performances,paving their ways towards practical applications.