Publication date: 15th July 2022
Solution processing of layers for organic light emitting diodes (OLEDs) is becoming more and more relevant in research and industry. As a highly scalable method to deposit organic, hybrid and emerging emitter materials it is capable of replacing today’s de-facto standard fabrication process of physical vapor deposition. Many commonly used materials, though, have a similar solubility in “standard” solvents such as toluene or tetrahydrofuran. To avoid redissolution of previously fabricated layers, a so-called orthogonal solvent system must be found. Especially for novel, emerging materials this proves to be a difficult task since not all material properties, such as the solubility in various solvents, are known immediately after synthesis. Crosslinking of polymeric materials has proven to be a viable solution to this problem in the past. In a reaction activated by light, by temperature or chemically, functional moieties link the polymer chains, rendering them less soluble. However, most reactive sides are specifically tailored to a type of polymer and have to be added in complicated synthesis steps. Additive crosslinkers can instead be added to a polymer solution and can work on different material types, making them more universally applicable. Especially in the case of novel materials, a universal crosslinker can readily be applied even when changes are made to parts of the chemical structure, which is often the case while developing a new emitter material. In this work we present a novel bisazide crosslinker to crosslink PPV materials and demonstrate its application with the well-known standard emitter Super Yellow. This provides a solvent resistance and allows for the processing of an additional electron blocking layer from the same solvent in an inverted OLED stack. Device efficacy was found to be drastically improved by 56 % while the luminance even increases by 78 %. Doctor blading was used as a solution processing method to demonstrate the upscalability of solution processing techniques.[1] This technique of crosslinking can be applied to many other cases, including emerging materials.
This work was conducted in the framework of the Joint Lab GEN_FAB and was supported by the HySPRINT innovation lab at Helmholtz-Zentrum Berlin. Financial support by the German Federal Ministry of Education and Research (BMBF) through grant No. FKZ 13N13695 (POESIE) is gratefully acknowledged.
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