Branched hierarchical titanium dioxide nanoflower on carbon nanofiber with efficient scattering layer for high performance dye-sensitized solar cells

A new bilayered photoanode is fabricated for dye-sensitized solar cells (DSSCs) composed of the carbon nanofiber coated by hierarchical TiO2 nanoflower (CNF-TNF) as underlayer and the urchin-like TiO2 hollow sphere (UTHS) as light-scattering layer. The CNF-TNF with a large specific surface area of 336.5 m2 g−1 provides dual-functions of more dye loading and efficient charge transport, leading to the enhanced short-circuit photocurrent density of 21.40 mA cm−2 and prolonged electron lifetime of 189.2 ms. The incorporated carbon nanofiber not only reduces the interfacial resistance and the charge recombination rate, but also improves the light harvesting, resulting in a high photoelectric conversion efficiency (PCE) up to 8.57% for the single-layered CNF-TNF based DSSC. In addition, by optimizing the surface morphology of TiO2 hollow sphere, we obtain the unique 3D UTHS, exhibiting strong light-scattering effect and low charge recombination due to the favorable connection among spheres provided by modified porous shell. As a consequence, an overall PCE of 9.21% is achieved for CNF-TNF+UTHS based DSSC, which is far superior to that of P25 based DSSC (5.10%). To the best of our knowledge, it is the first time that the hierarchically CNF-TNF composite is synthesized and utilized for enhanced efficiency DSSCs.