TiO2 coated urchin-like SnO2 microspheres for efficient dye-sensitized solar cells

Urchin-like SnO2 microspheres have been grown for use as photoanodes in dye-sensitized solar cells (DSSCs). We observed that a thin layer coating of TiO2 on urchin-like SnO2 microsphere photoanodes greatly enhanced dye loading capability and light scattering ability, and achieved comparable solar cell performance even at half the thickness of a typical nanocrystalline TiO2 photoanode. In addition, this photoanode only required attaching similar to 55% of the amount of dye for efficient light harvesting compared to one based on nanocrystalline TiO2. Longer decay of transient photovoltage and higher charge recombination resistance evidenced from electrochemical impedance spectroscopy of the devices based on TiO2 coated urchin-like SnO2 revealed slower recombination rates of electrons as a result of the thin blocking layer of TiO2 coated on urchinlike SnO2. TiO2 coated urchin-like SnO2 showed the highest value (76.1 ms) of electron lifetime (tau) compared to 2.4 ms for bare urchin-like SnO2 and 14.9 ms for nanocrystalline TiO2. TiO2 coated SnO2 showed greatly enhanced open circuit voltage (V (oc)), short-circuit current density (J (sc)) and fill factor (FF) leading to a four-fold increase in efficiency increase compared to bare SnO2. Although TiO2 coated urchin-like SnO2 showed slightly lower cell efficiency than nanocrystalline TiO2, it only used a half thickness of photoanode and saved similar to 45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO2.