Rational design of a tripartite-layered TiO2 photoelectrode: a candidate for enhanced power conversion efficiency in dye sensitized solar cells

Abstract

A tri-layered photoelectrode for dye-sensitized solar cells (DSSCs) is assembled using single crystal hollow TiO₂ nanoparticles (HTNPs), sub-micro hollow TiO₂ mesospheres (SHTMSs) and hierarchical TiO₂ microspheres (HTMSs). The bottom layer composed of single crystal hollow TiO₂ nanoparticles serves to absorb dye molecules, harvest light due to its hollow structure and keep a better mechanical contact with FTO conducting glass; the middle layer consisting of sub-micro hollow mesospheres works as a multifunctional layer due to its high dye adsorption ability, strong light trapping and scattering ability and slow recombination rates; and the top layer consisting of hierarchical microspheres enhances light scattering. The DSSCs made of photoanodes with a tripartite-layer structure (Film 4) show a superior photoconversion efficiency (PCE) of 9.24%, which is 7.4% higher than a single layered photoanode composed of HTNPs (Film 1: 8.90%), 4.6% higher than a double layer-based electrode consisting of HTNPs and SHTMSs (Film 2: 9.03%) and 2.6% higher than a double layer-based electrode made of HTNPs and HTMSs (Film 3: 9.11%). The significant improvements in the PCE for tri-layered TiO₂ photoanodes are mainly because of the combined effects of their higher light scattering ability, long electron lifetime, fast electron transport rate, efficient charge collection and a considerable surface area with high dye-loading capability. This study confirms that the facile tri-layered photoanode is an interesting structure for high-efficiency DSSCs.