Addressing Thermal Stability Challenges in Top‐Emission OLEDs: The Role of Buffer Layer in Preventing Pixel Shrinkage

Abstract This study introduces a strategic buffer layer approach to mitigate thermal‐induced pixel shrinkage in top‐emission organic light‐emitting diodes (TEOLEDs), enhancing both thermal stability and efficiency. A new cathode composed of binary alloy from silver (Ag) and copper (Cu) is developed for their moderately high binding energy, improving film uniformity and boosting optical and electrical performance. High surface energy metals, aluminum (Al) and Cu are employed as buffer layers to regulate the growth mechanism, resulting in an exceptionally smooth cathode film. The optimal device is designed by incorporating a bilayer electron injection layer consisting of lithium fluoride (LiF) and ytterbium (Yb) along with the buffer layer. The TEOLEDs achieved an impressive efficiency of 178 cd A⁻¹ and luminance of 247,000 cd m⁻² while demonstrating superior thermal stability, with the absence of cathode shrinkage after 240 h at 85 °C. This stability is attributed to the suppression of thermal diffusion and aggregation, facilitated by the high surface energy buffer layer and innovative cathode compositions employed.