Effect of the TiO2 shell thickness on the dye-sensitized solar cells with ZnO–TiO2 core–shell nanorod electrodes

Abstract Well-aligned ZnO nanorod arrays with high aspect ratio have been grown on FTO substrate by hydrothermal process. FTO substrate was pre-modified with ZnO thin film as a seed layer by sol–gel coating. TiO 2 thin shells with different thicknesses were grown on the ZnO nanorods by chemical vapor deposition method. Sample characterization was performed by X-ray diffraction (XRD), electron microscopy (FESEM, TEM, and SAD), X-ray photoelectron spectroscopy (XPS) and UV–vis Spectroscopy. XRD and TEM analyses indicated a wurtzite structured with high crystallinity and confirmed that each individual ZnO nanorod was a single crystal. The photoelectrochemical experiments were performed in a sandwich type two-electrode cell and I – V curves were obtained. Result of solar cell testing showed that addition of TiO 2 shells to ZnO nanorod significantly increased the J SC , V OC , fill factor and efficiency relative to devices without TiO 2 shells. Overall cell efficiency jumped from 0.45% for bare ZnO nanorod array to 0.92% for 14 nm thick TiO 2 shells on ZnO which showed a twofold increase. The fill factor increased from 0.37 to 0.60, showing a 62% improvement. For a shell with thickness of 21 nm, V OC increased by about 150 mV to 0.68 V. The results showed that it is possible to fabricate core–shell cells of higher efficiency by using nanorod arrays and other morphologies with larger surface area.

[1]  Zhong Lin Wang.  ZnO Nanowire and Nanobelt Platform for Nanotechnology , 2009 .

[2]  Tomas Edvinsson,et al.  Comparison of Dye-Sensitized ZnO and TiO2 Solar Cells: Studies of Charge Transport and Carrier Lifetime , 2007 .

[3]  Hong Liu,et al.  Degradation mechanism of ZnO-based dye-sensitized solar cells , 2010 .

[4]  Peidong Yang,et al.  ZnO-TiO2 Core-Shell Nanorod/P3HT Solar Cells , 2007 .

[5]  Mikkel Jørgensen,et al.  Fabrication of Polymer Solar Cells Using Aqueous Processing for All Layers Including the Metal Back Electrode , 2011 .

[6]  D. Lincot,et al.  Electrodeposition of semiconductors for optoelectronic devices: results on zinc oxide , 2000 .

[7]  G. Khang,et al.  Effect of hydroxylamine hydrochloride on the floral decoration of zinc oxide synthesized by solution method , 2008 .

[8]  R. M. Mehra,et al.  Synthesis of nanocrystalline ZnO powder via sol–gel route for dye-sensitized solar cells , 2008 .

[9]  B. Vertruyen,et al.  Study of ZnO sol–gel films: Effect of annealing , 2010 .

[10]  Moon-Ho Ham,et al.  ZnO-nanowire-inserted GaN/ZnO heterojunction light-emitting diodes. , 2007, Small.

[11]  F. Krebs,et al.  Hybrid solar cells based on MEH-PPV and thin film semiconductor oxides (TiO2, Nb2O5, ZnO, CeO2 and CeO2–TiO2): Performance improvement during long-time irradiation , 2006 .

[12]  R. Rajapakse,et al.  The interconnected CaCO3 coated SnO2 nanocrystalline dye-sensitized solar cell with superior performance , 2011 .

[13]  K. Pan,et al.  Al2O3-coated SnO2/TiO2 composite electrode for the dye-sensitized solar cell , 2005 .

[14]  Xiaoyan Hu,et al.  CdSe nanocrystal sensitized ZnO core-shell nanorod array films: Preparation and photovoltaic properties , 2009 .

[15]  Suren A. Gevorgyan,et al.  An inter-laboratory stability study of roll-to-roll coated flexible polymer solar modules , 2011 .

[16]  Xingzhong Zhao,et al.  The effect of growth conditions on the properties of ZnO nanorod dye-sensitized solar cells , 2008 .

[17]  C. Lokhande,et al.  CBD grown ZnO-based gas sensors and dye-sensitized solar cells , 2009 .

[18]  M. Swaminathan,et al.  An efficient nanostructured ZnO for dye sensitized degradation of Reactive Red 120 dye under solar light , 2011 .

[19]  Anders Hagfeldt,et al.  A 5% efficient photoelectrochemical solar cell based on nanostructured ZnO electrodes , 2002 .

[20]  M. Grätzel,et al.  A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films , 1991, Nature.

[21]  Kwang-H Lee,et al.  An Almost Transparent Image Pixel with a Pentacene/ZnO Photodiode, a Pentacene Thin‐Film Transistor, and a 6,13‐Pentacenequinone Phosphor Layer , 2011, Advanced materials.

[22]  Frederik C. Krebs,et al.  Life-cycle analysis of product integrated polymer solar cells , 2011 .

[23]  Mauricio Ortega-López,et al.  Improved efficiency of the chemical bath deposition method during growth of ZnO thin films , 2003 .

[24]  Hyung-Kee Seo,et al.  Room temperature synthesis of needle-shaped ZnO nanorods via sonochemical method , 2007 .

[25]  D. Basak,et al.  Effect of thermal annealing treatment on structural, electrical and optical properties of transparent sol–gel ZnO thin films , 2005 .

[26]  Aleksandra Radenovic,et al.  ZnO-Al2O3 and ZnO-TiO2 core-shell nanowire dye-sensitized solar cells. , 2006, The journal of physical chemistry. B.

[27]  C. Jagadish,et al.  Review of zincblende ZnO: Stability of metastable ZnO phases , 2007 .

[28]  U. Gösele,et al.  Laser-interference lithography tailored for highly symmetrically arranged ZnO nanowire arrays. , 2007, Small.

[29]  Xiao Wei Sun,et al.  Hydrothermally grown oriented ZnO nanorod arrays for gas sensing applications , 2006 .

[30]  Zi-Qiang Xu,et al.  Characteristics of Al-doped c-axis orientation ZnO thin films prepared by the sol-gel method , 2006 .

[31]  Chen-Hao Ku,et al.  Chemical bath deposition of ZnO nanowire–nanoparticle composite electrodes for use in dye-sensitized solar cells , 2007 .

[32]  Guozhong Cao,et al.  ZnO Nanostructures for Dye‐Sensitized Solar Cells , 2009 .

[33]  Seeram Ramakrishna,et al.  Nb2O5 Photoelectrodes for Dye-Sensitized Solar Cells: Choice of the Polymorph , 2010 .

[34]  M. S. Akhtar,et al.  Controlled synthesis of various ZnO nanostructured materials by capping agents-assisted hydrothermal method for dye-sensitized solar cells , 2008 .

[35]  S. Fujihara,et al.  Effect of an Nb2O5 nanolayer coating on ZnO electrodes in dye-sensitized solar cells , 2011 .

[36]  Mikkel Jørgensen,et al.  Aqueous processing of low-band-gap polymer solar cells using roll-to-roll methods. , 2011, ACS nano.

[37]  B. Yan,et al.  Growth mechanism and diameter control of well-aligned small-diameter ZnO nanowire arrays synthesized by a catalyst-free thermal evaporation method , 2009, Nanotechnology.

[38]  Lisha Zhang,et al.  Electrodeposited nanoporous ZnO films exhibiting enhanced performance in dye-sensitized solar cells , 2006 .

[39]  Vidhya Chakrapani,et al.  Band‐Edge Engineered Hybrid Structures for Dye‐Sensitized Solar Cells Based on SnO2 Nanowires , 2008 .

[40]  S. Sharma,et al.  Photovoltaic devices based on PPHT: ZnO and dye-sensitized PPHT: ZnO thin films , 2008 .