Abstract
Aluminum tris(8‐hydroxyquinoline) (Alq3), which is utilized as an electron transport layer (ETL) in organic light emitting diodes (OLEDs) is known to form crystalline domains over time. This morphological instability plays an important role in OLED degradation. In this study, crystallization was suppressed via entropic stabilization by blending Alq3 with a close adduct of the same i.e., aluminum tris(4 methyl, 8‐hydroxyquinoline) (4m‐Alq3). X‐ray diffraction studies at elevated temperatures indicate that the blend remains amorphous even after 96 hr of annealing at 160°C. OLED devices were fabricated and investigated for Alq3, 4m‐Alq3, and a co‐evaporated 50/50% mixture (blend) of Alq3 and 4m‐Alq3. As expected, the blend device possessed both the highest resistance and quantum efficiency over the entire current density range. Devices made with 4m‐Alq3 showed the highest current density, yet their quantum efficiency and lifetime were significantly lower than that of Alq3. In spite of the morphological stability of the blend, the intrinsic instability of 4m‐Alq3 was found to play a more important role in device degradation. This study indicates that while entropic stabilization is an effective way of obtaining brighter and more efficient OLEDs, care must be taken to ensure electrochemical stability and interfacial energy‐level optimization for both components.
Published Version
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