Exploring the fabrication of solution-processed OLEDs

Abstract

Solution-processable organic light-emitting diodes (OLEDs) are of significant interest for optoelectronic devices such as screens and lighting because they can enable low-cost and scalable manufacturing, especially in large areas and flexible substrates. Conventional OLEDs are typically fabricated with vacuum deposition which increases the cost and complexity of manufacturing. Developing OLED architectures that can be fabricated from solution and without the need for vacuum or highly costly equipment is of interest given the wide use of OLEDs. This work investigates the fabrication of OLED devices using predominantly solution-processed layers and examines the associated limitations related to film formation, layer compatibility, and device fabrication. The primary goal was to realize a fully solution-processed OLED device. In the absence of a fully functional solution-processed device, the objective was to fabricate operational devices containing as many solution-processed layers as possible while identifying the key challenges preventing complete implementation. A small emphasis was placed on the electrodes. The anode is PEDOT:PSS that is already utilized as a hole transport layer in conventional OLEDs. Given its high optical transparency, electrical conductivity and ability to enhance it, and ease of processing, it could also work as an electrode in an OLED device. The top electrode is a network of silver nanowires deposited by spray coating. Other layers – F8BT, PEI, ZnO nanoparticles (and PEDOT:PSS) - are deposited by spin coating. Four OLED device architectures were fabricated and characterized, of which one architecture yielded functional devices. The operational devices had indium tin oxide (ITO) as the anode and thermally evaporated aluminium as the cathode, meaning that a fully solution-processed OLED was not achieved. However, the working devices incorporated four solution-processed layers out of a total of six layers. The best-performing devices exhibited an external quantum efficiency (EQE) of approximately 0,1%, a turn-on voltage of approximately 6 V, and a current efficiency of approximately 0,4 cd/A.