Effects of a 2 nm thick Al2O3 buffer layer in metal auxiliary electrode on lifetime and stable operation of large-area organic light emitting diodes

• Buffer layer effect in auxiliary electrode on the lifetime of OLEDs investigated.
• 2 nm thick Al2O3 was introduced to Mo–Al–Mo auxiliary electrode.
• Trapezoidal etch profiles were obtained without undercuts or voids.
• OLED with buffer layer showed no hot spots and non-emission areas for 40,000 h.
• Lifetime of large-area OLED were greatly improved by buffer layer.

We have investigated the buffer layer effect in the auxiliary electrode on the lifetime and stable operation of large-area organic light-emitting diodes (OLEDs). A 2-nm-thick Al2O3 layer was introduced between the Mo and Al in a conventional Mo–Al–Mo metal auxiliary electrode structure. The structure of the buffer layer inserted auxiliary electrode is Mo–Al–Al2O3–Al–Al2O3–Al–Mo. By introducing the 2-nm-thick Al2O3 buffer layers, the etch rate of the Al layer was effectively controlled, which can prevent the formation of undercut structures in the metal auxiliary electrode caused by the different etch rates of Mo and Al. A trapezoidal etch profile was obtained from the Al2O3 buffer layer inserted metal auxiliary electrode structure; the profile did not contain undercuts or voids. The buffer layer inserted auxiliary electrode was used when fabricating a 30 × 120 mm2 green emission OLED lighting panel. The lifetime of the OLEDs devices with buffer layer introduced metal auxiliary electrode reached 40,000 h for the LT 70 condition, which is around four times longer than that obtained from OLEDs without the buffer layers.

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