Cesium polytungstate in sputtered solar control films. I. Microstructure and optical properties

Sputtered thin films with strong near-infrared absorption and high visible transmission and electrical resistivity (& GE;10(2) omega cm) have been obtained using highly conductive cesium tungsten bronze targets. The origin of the low electrical conductivity and high near-infrared absorption of the films has been investigated by focusing on internal defects and reported in two parts. In Paper I, the optical and electrical properties of the films and their microstructural characterization using x-ray diffraction and high-resolution transmission electron microscopy are presented. Abundant planar W and Cs defects were found on hexagonal prismatic planes that locally expanded the defect plane and triggered the hexagonal-to-orthorhombic crystallographic transition. These cationic defects diminished conduction electrons and suppressed electrical conduction, whereas oxygen vacancies generated W5+-trapped electrons to activate polaronic excitations for strong near-infrared absorption.