Amit Thapa1,§, Jiantao Zai2,§, Hytham Elbohy1, Prashant Poudel1, Nirmal Adhikari1, Xuefeng Qian2 (*), and Qiquan Qiao1 (*)
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1 Center for Advanced Photovoltaics, Department of Electrical Engineering, South Dakota State University, Brookings, SD, 57007, USA 2 School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China § These authors contributed equally to this work.
Keywords:TiO2 coating, dye-sensitized solar cells, urchin-like, SnO2
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 per- formance even at half the thickness of a typical nanocrystalline TiO2 photoanode. In addition, this photoanode only required attaching ~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 urchin- like SnO2. TiO2 coated urchin-like SnO2 showed the highest value (76.1 ms) of electron lifetime (τ) 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 (Voc), short-circuit current density (Jsc) 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 ~45% of the amount of dye for efficient light harvesting compared to normal nanocrystalline TiO2.