Microsphere Assembly of TiO₂ Rectangular Nanotubes: Facile Fabrication and Photovoltaic Property

Graphical abstract: Novel TiO₂ rectangular nanotube constructed hierarchical microspheres (TRTMs) were fabricated. The photoanode using TRTMs as the top scattering layer enhanced the light harvesting ability by reflecting the transmission light again into the P₂₅ sub-layer, thus contributed to the high electron density and increase the conversion efficiency. The overall conversion efficiency shows 40.9% increment even though the dye adsorption is 45.8% lower than that of pure P₂₅ photoanode. - Highlights: • Microsphere assembly of TiO₂ rectangular nanotubewere fabricated. • Thepossible formation mechanism of the hollow structure was proposed. • The obtained sample was used as the scattering layer to enhance the light harvesting. • PCE shows a 40.9% increment though dye adsorption is 45.8% lower than that of pure P_25. - Abstract: Novel hierarchical microspheres constructed with TiO₂ rectangular nanotubes (TRTMs) were fabricated via a facile route. The obtained samples were investigated by the field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The FESEM results showed that the solid cuboids precursor become rectangular and hollow TiO₂ nanotube after calcination at 500 °C for 3 h. The XRD spectra and TEM results confirmed that crystalline anatase TiO₂ was formed. Meanwhile, a possible mechanism for the formation of the hollow structure was also briefly proposed. The prepared TRTMs were applied as the scattering layer on the top of Deguss P₂₅ nanoparticles thin film and were then used as the photoanode of dye-sensitized solar cell (DSSCs). This prepared photoanode had enhanced light harvesting capabilities due to the ability to reflect the transmission light into the P₂₅ sub-layer, which ultimately led to an increase in the electron density. The EIS spectra showed that the optimized photoanode using TRTMs as the scattering layer is benificial for electron transport due to the synergistic effect of the excellent light-scattering ability of TRTMs and the relatively high dye adsorption amount of P₂₅ sublayer. An overall conversion efficiency of 7.34% was obtained for the optimized bi-layer photoanode, and a 40.9% increment in conversion efficiency was achieved even though the dye adsorption is 45.8% lower than that of pure P₂₅ photoanode.