Photo-assisted deposition of Ag nanoparticles on branched TiO2 nanorod arrays for dye-sensitized solar cells with enhanced efficiency

Abstract

In this paper, a novel photoanode based on Ag NPs decorated branched TiO2 nanorod arrays (BTNR/Ag) was developed, aiming to utilize the comprehensive advantages of fast electron transport and large surface area of one-dimensional TiO2 hierarchical structure as well as the surface plasmon resonance (SPR) effect of Ag NPs for improving the photovoltaic performance of dye-sensitized solar cells (DSSCs). The hierarchical BTNR with abundant branches exhibits a novel matrix for Ag NPs deposition by a facile photo-reduction method. It is interesting that the Ag NPs demonstrate a typical size gradient distribution on BTNR. The high density small Ag NPs (less than 10 nm) at the middle part of BTNR are benefit for photo-generated electrons separation and transfer in dye-sensitized BTNR/Ag, while the large Ag NPs at the upper part of BTNR can act as light scattering layer to enhance light harvesting. The incorporation of Ag NPs in the hybrid nanostructure can also improve the dye-loading. As a result, the DSSC based on BTNR/Ag with appropriate content of Ag NPs exhibits higher power conversion efficiency than the DSSC based on pristine BTNR. However, the deposition of excess Ag NPs in BTNR/Ag causes loss of internal surface area and strong charge recombination, leading to decrease of efficiency. The DSSC based on BTNR/Ag synthesized at a 2 mmol L−1 AgNO3 solution shows the highest conversion efficiency, improved by 51.3% compared with the pristine BTNR-based DSSC.