Correlation between energy-level alignment and interfacial properties with the OLED performance

Abstract Solution-processable organic light emitting diodes (OLEDs) are emerging as the most promising next-generation lighting technology. However, the up-scaling and the roll-to-roll production of this solid-state lighting technology remain a great challenge up to this day. One of the key factors that determines the performance of an OLED device is the balanced and effective injection/transport of charge carriers from the electrodes to the emitting layer. Injection and transport of carriers can be significantly affected by internal factors such as the energy-level alignment and the integrity of the interfaces formed between the individual thin films of the stacked architectures of the devices. In this work, various charge transport layers, such as Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), Poly(9,9-dioctylfluorene- alt-N(4-sec-butylphenyl)-diphenylamine (TFB), Copper(I) thiocyanate (CuSCN) and Poly[9,9-dioctyl-9′,9′-bis[3-(trimethylamomonio)propyl][2,2′-bi-9 H-fluorene]-7,7′-diyliodide (PFN-I), are grown as thin films by spin coating and characterized. Following this, the fabrication of multilayer OLED devices was carried out for the comparative evaluation of the performance and functional properties. It was found that the energy level alignment of various functional layers, along with the morphological quality of the mixed interlayers between these layers, are strongly correlated with the accumulation and trapping of carriers during the device’s operation. This directly affects the performance and operation of the OLED devices, including brightness, electrical characteristics, and emission profile.