LAUSR

Abstract A surfactant-free synthesis of small-sized tungsten trioxide is presented. Nanoparticles with an average size of 4.6 ± 1.5 nm are prepared via hot-injection techniques in ethanol. Due to the reducing properties of ethanol, a sub-stoichiometry composition WO3-x (x∼0.4) is obtained. The partial reduction of W+VI to W+V becomes visible in the bluish color of suspensions and powder samples and in optical spectroscopy (UV-Vis). The nanoparticles are further characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDXS) and infrared spectroscopy (FT-IR). Due to their small size, their high colloidal stability and the absence of surfactants, layers from the as-prepared WO3-x nanoparticles are ideally suited to form anode buffer layers in organic solar cells. Exemplary solar cells show good power conversion efficiency of 6.3%.