Sr, Zn co-doped TiO2 xerogel film made of uniform spheres for high-performance dye-sensitized solar cells

Abstract

This study comes up with the facile preparation of Sr,Zn co-doped TiO2 xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs). The film contains 2.5-μm-diameter spheres assembled from 60 nm nanoparticles. X-ray photoelectron spectroscopy (XPS) shows that Sr2+ and Zn2+ ions to be well incorporated into the TiO2 crystal lattice without forming specific strontium and zinc compositions. The crystallite size, phase composition, and band structure of the spheres depend on the dopants concentration. Isolated energy levels near valence band as a result of the foreign ions introduction improve the photocatalytic activity of the prepared TiO2 spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 0.4 at.% Zn showed the highest power conversion efficiency of 7.87 % and short circuit current density of 18.75 mA cm−2 thanks to lower charge transfer resistance (2.16 Ω cm2), lower electron transit time (1.19 ms), and higher electron diffusion coefficient (18.1 × 104 cm2 S−1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of the simultaneous introduction of alkaline earth ions and transition ions into TiO2 xerogel films will open up a new insight into the fabrication of high performance DSCs.