Preparation of ordered porous SnO2 films by dip-drawing method with PS colloid crystal templates

Ordered macroporous SnO2 thin films were fabricated by using colloid crystal template of polystyrene (PS) spheres. Efficient dip-drawing method was used in both PS template assembly and the fabrication of porous structure. The PS templates were orderly assembled on clean glass substrates through colloid crystallization of monodisperse PS latex spheres, which were synthesized by an emulsion polymerization technique. The porous SnO2 thin films were prepared through filling SnO2 precursor sol into the spaces among the close-packed PS templates, and then annealing at 500 °C to remove the PS spheres and form SnO2 crystal wall. The forming mechanism of PS templates through dip-drawing method was explained based on three driving forces existing in the assembly processes. The SnO2 sol concentration and PS sphere size had important effects on formation of ordered porous structure The X-ray diffraction (XRD) spectra indicated the thin film was rutile structure and consisted of nanometer grains. The transmittance spectrum showed that optical transmittance kept above 80% beyond the wavelength of 440 nm. Optical band-gap of the porous SnO2 film was 3.68 eV.