Enhanced OLED performance upon photolithographic patterning by using an atomic-layer-deposited buffer layer

This study addresses the problem of patterning-induced degradations to organic light-emitting diodes (OLEDs) by using a thin (10 Å) atomic-layer-deposited (ALD) Al₂O₃ film as both an electron-injection layer and a protecting layer for the electroluminescent material, poly[1-methoxy-4-(2′-ethyl-hexyloxy)-2,5-phenylene vinylene] (MEH-PPV). With the ALD Al₂O₃ film, the OLEDs not only withstood an aggressive photolithographic patterning process without any degradation but unprecedentedly showed increased luminous efficiency (by 100%) and lowered turn-on voltage (by 19%) afterward. Although the ALD precursor, trimethylaluminum (TMA), was found to damage the MEH-PPV layer through electrophilic addition to the vinylene groups of MEH-PPV during the deposition of the Al₂O₃ film, its damaging effect was eliminated by pre-treating the MEH-PPV surface with isopropyl alcohol (IPA), whose hydroxyl groups scavenged TMA throughout the ALD process. The performance of the photo-patterned OLEDs was further improved by using a high-conductivity hole-injection layer, which increased accumulation of holes at the EL–buffer interface to enhance electron injection. The method reported herein improves the applicability of photolithography to OLED fabrication, promising to resolve the issue of patterning that has in part impeded OLED’s commercialization.