Formation of Ag+–N–TiO2 nanochains and their HPA-composites as highly visible light-sensitive photocatalysts toward two-color solar cells

Abstract

Ag⁺-coupled N-doped TiO₂ (Ag⁺–N–TiO₂) nanochains were newly synthesized by combination of sol–gel and hydrothermal methods, and their structures were characterized by TEM, SEM, and XPS. The UV-visible diffuse reflectance absorption spectrum of Ag⁺–N–TiO₂ nanochains was observed to absorb visible light in the broad range of 400–800 nm as compared to neat N–TiO₂, exhibiting efficient visible light-photocatalytic activity. Their visible light absorption band became much broader and stronger upon formation of composites with heteropoly phosphotungstic acid (HPA), and their photocatalytic efficiency was observed to be further enhanced. The Ag⁺–N–TiO₂ nanochains also exhibited improved photovoltaic performance with significantly high photoenergy conversion efficiency (PCE) (5.6%) under AM 1.5 (100 mW cm⁻²) as compared to N–TiO₂ nanochains. The PCE was observed to be further enhanced to 7.6% by formation of HPA-composites. These results suggest that Ag and HPA play important roles in enhancement of PCE through the cooperative Z-scheme process of the electron transport triggered by two-color visible lights as in the plant photosynthetic system. The HPA-composites were also found to be useful for the dye-sensitized solar cells (DSSCs) as proved by synergistic enhancement of PCE to 10.2% as they are additionally incorporated with Ru-dye.