Interfacial engineering and configuration design of bilayered photoanode consisting of macroporous tin dioxide/titanium dioxide for high performance dye-sensitized solar cells

Highlights: • Hierarchical SnO₂/TiO₂ porous nanostructure combines fast electron transport, slow charge recombination and high specific surface area. • SnO₂@TiO₂ hollow sphere synthesized by a facile water bath method exhibits superior light scattering ability. • High efficiency of 7.79% is achieved for double layered photoanode based on macroporous SnO₂/TiO₂ composite nanomaterials. - Abstract: Two kinds of tin oxide (SnO₂)/titanium oxide (TiO₂) composite materials have been synthesized and applied as electrodes in dye-sensitized solar cells (DSSCs) with high performance. The porous SnO₂/TiO₂ material (PSTM) consisting of SnO₂ nanosheets cluster and TiO₂ nanoparticles (P25) shows a superior dye adsorption ability due to its large specific surface area (151.1 m² g⁻¹). The PSTM based cell exhibits the slowest electron recombination rate among the cells tested from electrochemical impedance spectra measurements, and obtains final power conversion efficiency (PCE) up to 6.80%. Another novel structure of SnO₂@TiO₂ hollow sphere (STHS) prepared via a facile water bath process is designed to improve the light utilization efficiency with its excellent light scattering ability. Though the charge recombination resistance of STHS (25.6 Ω) is smaller than that of P25 (30.6 Ω), the PCE of the DSSCs based on the former is 5.82%, showing over 9.2% increment than the latter (5.33%). This can be mainly ascribed to the enhanced light-harvesting ability and charge collection efficiency of the macroporous hollow sphere structure, both of which contribute to a higher short current density and hence for the better photovoltaic performance. Furthermore, we demonstrate a bilayered film of PSTM (charge conduction layer) and STHS (light scattering layer) as photoanode aiming to further improve the efficiency of DSSC by engineered integration of different promising materials. The results indicate that the PSTM+STHS based cell shows an obvious 14.6% increase of PCE (7.79% with a J_sc of 17.49 mA cm⁻², V_oc of 0.73 V and FF of 0.61) as compared to the single layered PSTM photoelectrode with the same thickness of ∼6.9 μm, providing the specific evidence for taking full advantages of the superior dye adsorption, fast charge collection as well as strong light harvesting simultaneously. Fundamentally, this study not only provides a scheme for the guidance of effective materials surface and interfacial modification, but also highlights the significance of the ideal photoanode configuration for high-efficiency solar cells application