Facile fabrication of crack-free TiO2 inverse opal thin-film and its application as electron transporting scaffold for efficient Sb2S3-sensitized solar cells

Uniform and crack-free TiO2 inverse opal thin-films were successfully fabricated by simple template immersion method in pre-hydrolyzed TiCl4 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 prehydrolyzed TiCl4 precursor solution to infiltrate the templates without inducing defects. By repeated soaking and drying process, and subsequent calcination, non-uniform and crack defects-free TiO2 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. Also, as an improvement to conventional approach, this facile fabrication method is adaptable for industrial scale-up. The resulting well-developed porous TiO2 inverse opal thin-films were applied for photovoltaic clean energy conversion as electron transporting scaffolds in antimony sulfide (Sb2S3) sensitized solar cells which had high power conversion efficiency of 7.30 % (1 sun), 8.56 % (0.5 sun), and 8.34 % (0.1 sun); showcasing improved device performance over previously reported mesoporous Sb2S3-sensitized solar cells.