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

摘要

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 (eta(th)), electron injection efficiency (eta(inj)) and electron collection efficiency (eta(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 lev(e)l trapping amounts to decrease electron recombination tosses. The fully flexible DSSCs assembled by TiO2 NWAs/2.4 mot% 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%).