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) cm(2) · 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.