Enhancing Tandem Organic Light-Emitting Diode Performance with Multiple Electroluminescent Units

Tandemorganic light-emitting diodes (TOLEDs) which stackmultipleelectroluminescent units (EUs) via a charge-generation layer (CGL)are advanced device designs that improve the electroluminescent (EL)performance and operating lifetime. However, each CGL used in a devicewith multiple EUs is affected by electrodes and the other CGLs, resultingin a suboptimal ability to generate carriers and thus decreasing deviceefficiency and luminance values. Herein, four specific designs, includingan effective CGL structure, an exciplex host for the emitting layer(EML), simplified device architectures, and nanoparticle-based diffusers,are proposed to realize highly efficient TOLEDs, aiming to sustainor even surpass the external quantum efficiency linearity with thenumber of stacked EUs. Aside from the heterojunction structure ofthe CGL, the n-type electron injection layer also plays a criticalrole in efficient charge generation. In addition, the exciplex hostused in the EML could improve the carrier balance and reduce the operatingvoltages. The EL efficiency of the three-stacked tandem device reaches78.7% (303.5 cd A(-1)), about 2.5 times that of theconventional device, which fails to meet the expected value. Whena nanoparticle-based diffuser layer was inserted between the substrateand the anode of the three-stacked TOLEDs, the EL efficiency of thedevice rose to 123.9% (456.9 cd A(-1)), about 3.9-foldthat of the conventional device. Furthermore, an ultra-high maximumluminance of 411,531 cd m(-2) could be obtained, exceedingthat of the conventional device by 5.8 times. Notably, the maximumcurrent efficiency of device T3D reaches record highscompared to the reported green TOLEDs. These results demonstrate theviability of practical design strategies for TOLEDs with multipleEUs for realizing high EL efficiency and luminance values, thus fulfillingthe requirements for OLED phototherapy and display applications.

Automated summary

By utilizing effective CGL structure, exciplex host in the EML, simplified device architecture, and nanoparticle-based diffusers, highly efficient TOLEDs can be achieved, surpassing the expected external quantum efficiency linearity and significantly increasing the luminance values.