Enhanced photovoltaic performance of dye-sensitized solar cells based on Sr-doped TiO2/SrTiO3 nanorod array heterostructures

Abstract

We present a novel Sr-doped TiO₂/SrTiO₃ nanorod array heterostructure for dye-sensitized solar cells (DSSCs) via a facile two-step hydrothermal process, with a tunable microstructure, optical response and photoelectrical conversion properties. The chemical composition components and microstructures of Sr-doped TiO₂/SrTiO₃ nanorod array heterostructures are investigated using XRD, XPS, SEM and TEM characterization techniques, respectively. It is shown that the treatment of rutile TiO₂ nanorod arrays in Sr(NO₃)₂ solution results in the self-doping of Sr into the lattice of TiO₂ and formation of Sr-doped TiO₂/SrTiO₃ nanorod array heterostructures, inducing a transition of optical response properties from the ultraviolet region to the visible region. The photogenerated electrons and holes can be effectively separated due to the formation of SrTiO₃/Sr-doped TiO₂ heterostructures with a uniquely matched band-gap energy structure, resulting in greatly enhanced photoelectric conversion efficiency performance. Electrochemical impedance spectroscopy and photoluminescence results show that the formation of Sr-doped TiO₂/SrTiO₃ heterostructures can effectively prolong the charge carrier lifetime. The dye loading capacity on the Sr-doped TiO₂/SrTiO₃ heterostructures can be improved through the functionalization bonding of the hydroxide group on the surface of the electrode material. DSSCs based on the optimized Sr-doped TiO₂/SrTiO₃ heterostructure photoanode achieve the highest energy conversion efficiency of 4.70% (one sun illumination), nearly 1.5 times higher than the bare rutile TiO₂ photoanode (3.10%).