Hydrothermal synthesis of TiO2 nanoparticles doped with trace amounts of strontium, and their application as working electrodes for dye sensitized solar cells: tunable electrical properties & enhanced photo-conversion performance

Strontium (Sr) doped TiO2 nanoparticles are investigated with a view to studying the performance parameters of dye sensitized solar cells (DSSCs). Sr is used in trace levels (parts per million, ppm hereafter). The Sr doped TiO2 and undoped TiO2 nanoparticles are synthesized by the hydrothermal method and thin films of TiO2 electrodes are prepared using these particles (average grain size of 24 nm). The electrodes are characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), surface area (BET) and UV-vis absorption spectrometry. DSSCs are fabricated using the doped and undoped TiO2 nanoparticle photoanodes. Their photovoltaic characteristics are studied by employing J-V measurements and electrochemical impedance spectroscopy (EIS). XRD studies reveal that the doping of Sr into the TiO2 lattice slightly inhibits the growth of the particles and causes lattice distortions. The optical studies indicate a reduction in band-gap upon doping of TiO2 films and a simultaneous enhancement in the photocurrent density (J(sc)) and the photovoltage (V-oc). The photoanode doped with 50 ppm Sr exhibits the highest power conversion efficiency (PCE) of about 7.88% which is 12.73% higher than that of undoped TiO2 cells. The effect of the Sr dopant on electron transport is studied by using EIS measurements. An improvement in electron life time is observed on the doping of TiO2.