Facile fabrication of crack-free TiO inverse opal thin-film and its application as electron transporting scaffold for efficient SbS-sensitized solar cells.

Uniform and crack-free TiO inverse opal thin-films were successfully fabricated by simple template immersion method in pre-hydrolyzed TiCl precursor solution even though it is difficult to fabricate crack-free inverse opals through conventional solution drop-casting sol-gel process. Here, mechanically robust polystyrene (PS) colloidal crystal template in which PS particles are linked by polyvinylpyrrolidone bridges, were immersed in pre-hydrolyzed TiCl precursor solution to infiltrate the templates without inducing defects. By repeated soaking and drying process, and subsequent calcination, non-uniform and crack defects-free TiO inverse opal thin-films were fabricated reproducibly because PS templates immersed in the precursor solution experienced consistent fluid flow into their pores at uniform precursor concentration together with suppressed capillary pressure during drying as a result of low infiltration rate per cycle.