Titanium mesh supported TiO2 nanowire arrays/Nb-doped TiO2 nanoparticles for fully flexible dye-sensitized solar cells with improved photovoltaic properties

Abstract

TiO₂ nanowire arrays (NWAs)/Nb-doped TiO₂ nanoparticles (NPs) composite structures were first synthesized on flexible titanium (Ti) meshes as a photoanode of dye sensitized solar cells (DSSCs) using a two-step hydrothermal and spin-coating approach. Three key factors, including the sunlight harvesting efficiency (η_lh), electron injection efficiency (η_inj) and electron collection efficiency (η_ec), which determine the conversion efficiency of flexible DSSC, are discussed in detail. The introduction of appropriate amounts of Nb-doping into the TiO₂ lattice was found to effectively improve the photovoltaic properties of flexible DSSCs. Mott–Schottky analysis showed that flat-band potential (V_fb) of the Nb-doped TiO₂ had a positive shift, which promoted photogenerated electron injection from dye molecules to the TiO₂ conduction band more energetically. The electrochemical impedance spectroscopy (EIS) measurement of the DSSCs under illumination demonstrated that photoelectrons could transfer faster in the Nb-doped TiO₂ composite. The EIS analysis in the dark indicated that slight Nb-doping reduced the shallow energy level trapping amounts to decrease electron recombination losses. The fully flexible DSSCs assembled by TiO₂ NWAs/2.4 mol% Nb-doped TiO₂ NPs photoanode and PEN/ITO-Pt photocathode displayed an increase in the J_sc value from 9.98 to 13.60 mA cm⁻² and V_oc from 0.74 to 0.78 V, thereby exhibiting a good 7.20% photovoltaic efficiency, which was superior to that of the undoped TiO₂ composite structures (4.96%).