Stacking multiple connecting functional materials in tandem organic light-emitting diodes

Abstract

Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency.

Highly efficient tandem organic light-emitting devices employing an easily fabricated charge generation unit

“…3(a). No significant spectrum narrowing and peak shifting are observed in device T-Ir(ppy) 3 compared with device S-Ir(ppy) 3 , and the emission pattern of device T-Ir(ppy) 3 obtained by using a PR650 SpectroScan spectrophotometer is very close to the desirable Lambertian distribution, which means that the optical microcavity effect can be neglected in the tandem device resulting from the superior optical transparency of the CGU, 17) and the improvement in current efficiency for the tandem device results from simultaneous emission in two emitting layers under driving curent density instead of the optical microcavity. Figure 3(b) illustrates the J-V and L-J characteristics of devices T-Ir(ppy) 3 and S-Ir(ppy) 3 .…”

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

“…), ,− metal–organic complexes (metal–phthalocyanine complexes CuPc, ZnPc, etc. ), , or fullerenes (C 60 and C 70 ). ,, These materials all have good charge generation ability, but they will partly absorb light in the visible light wavelength, thus decreasing device efficiency. In contrast, the organic/organic type CGL generally possesses high optical transmittance, a consistent and simple fabrication process, and low manufacturing temperatures. , As such, organic/organic CGLs are widely used due to their high availability.…”

A hybrid inorganic–organic light-emitting diode using Ti-doped ZrO2 as an electron-injection layer

“… 13 Efficiencies of HyLEDs were tuned by both hole/electron injection from metal oxide EIL into E LUMO of emissive layer. 20–28 Bolink et al , fabricated ITO/TiO 2 /F8BT/MoO 3 /Au HyLEDs results poor efficiences due to (i) higher energy barrier for injection from ITO to TiO 2 and (ii) poor hole blocking functionality of titania. 29 Therefore, it is urgent need to find alternate EILs which enable effective electron injection into emissive layer E LUMO .…”