Surface Coatings Based on Polysilsesquioxanes: Solution-Processible Smooth Hole-Injection Layers for Optoelectronic Applications

Optoelectronic devices usually consist of a transparent conductive oxide (TCO) as one electrode. Interfacial engineering between the TCO electrode and the overlying organic layers is an important method for tuning device performance. We introduce poly(methylsilsesquioxane)–poly(N,N‐di‐4‐methylphenylamino styrene) (PMSSQ–PTPA) as a potential hole‐injection layer forming material. Spin‐coating and thermally induced crosslinking resulted in an effective planarization of the anode interface. HOMO level (−5.6 eV) and hole mobility (1 × 10−6 cm2 · Vs−1) of the film on ITO substrates were measured by cyclovoltammetry and time‐of‐flight measurement demonstrating the hole injection capability of the layer. Adhesion and stability for further multilayer built‐up could be demonstrated. Contact angle measurements and tape tests after several solvent treatments proved the outstanding film stability. Poly(methylsilsesquioxane)–poly(N,N‐di‐4‐methylphenylamino styrene) (PMSSQ–PTPA) as potential hole‐injection layer (HIL) forming material was used for effective planarization of the anode interface. The obtained HIL showed high stability and adhesion even after several solvent treatments.