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4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 35 B4 - How does the nanostructure of TiO2 material affect the electron trapping/detrapping process in dye-sensitized solar cells? Hongxia Wang Queensland University of Technology, 2 George Street, Brisbane, 4001, AU One of the key components of a dye-sensitized solar cell (DSC) is the thin titanium dioxide (TiO2) film, which plays the role of anchoring the dye molecules and transporting the photogenerated electrons before they are collected by the external circuit. Conventional DSCs employ mesoporous TiO2 film consisting of nanoparticles (particle size: 20-30 nm) which are randomly connected together. Previous research has reported that the electron transport in the nano-particulates based network is 2-3 orders of magnitude lower than that of the bulk TiO2 material. [1] This unsatisfying electron transport property has direct impact on the performance of a DSC by influencing the electron collection efficiency. Thus nanostructures with orderly electron transport pathways such as nanowires and nanotubes have been proposed to replace the randomly connected nanoparticulates to overcome the issue of low electron transport in the TiO2 film. However, the photovoltaic performance of the DSCs with these 1-D order materials is generally lower than that of the nanoparticulates counterpart. This work aims to answer the following two questions: 1) Whether one-dimensional nanostructure is superior to the randomly connected nanoparticulates in terms of electron transport in the TiO2 film for DSCs? 2) How strong is the electron transport property dependent of the morphology of a material? Inorder to answer these questions, TiO2 materials with various morphologies including vertical grown 1-D nanorods on FTO substrate [2] and hierarchical structured spheres with 100% [001] facet exposed have been synthesized and characterized comprehensively in terms of the kinetics of electron transport and back reactions in the corresponding DSCs. The results indicated that the effective electron diffusion coefficient is actually not sensitive to the structure and shape of TiO2 material as assumed. However, the effective electron lifetime is strongly dependent on the morphology of TiO2 material. References [1] L.M. Peter. " J. Phys. Chem. C,"Characterization and modeling of dye-sensitized solar cells", 111, 6601-6612 (2007) [2] M. N. Liu, H.X. Wang, C. Yan, G. Will, J. Bell. "One-step synthesis of titanium oxide with trilayer structure for dyesensitized solar cells", Appl. Phys. Lett., 98, 133113 (2011) © SEFIN 2012
4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 36 B5 - 3D quantitative characterisation of a TiO2-based photoanode Giorgio Divitini a , Ole Stenzel b , Fabio Di Fonzo c , Carlo S. Casari c , Valeria Russo d , Andrea Li Bassi c , Volker Schmidt b , Caterina Ducati a a, Department of Materials Science & Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, GB b, Institute of Stochastics, Ulm University, 89069, Ulm, DE c, CNST - Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, via Pascoli 70/3, I-20133 Milano, IT d, Department of Energy and NEMAS – Center for NanoEngineered MAterials and Surfaces, Politecnico di Milano, via Ponzio 34/3, I-20133 Milano, IT Studying the micro- and nano-structure of the photoanode is vital in designing and manufacturing efficient dye-sensitised and hybrid solar cells. Transmission electron microscopy (TEM) is a good candidate for investigating such length scales, but the limitation of conventional TEM to extract only bi-dimensional information hinders our ability to have a full understanding of the three-dimensional structure and properties, particularly when the structure being analysed has a complex morphology. We instead apply advanced TEM techniques to characterise a photoanode prototype, combining high resolution crystallographic studies with three-dimensional information obtained from dark field electron tomography. In this work we present the study of a TiO2-based photoanode where the titania layer has been produced via pulsed laser deposition. The photoanode TiO2 layer is composed by small (10-20 nm) crystalline particles assembled in columnar aggregates, which constitute a forest-like film with high porosity (1). Such a hierarchical structure combines a large surface area with good electrical transport properties, leading to promising performance. We employed a dual beam FIB (FEI Helios Nanolab) to prepare a cross-section of a polymer heterojunction solar cell based on said photoanode and acquired a tilt series in a FEI Tecnai F20 (200 kV acceleration voltage). © SEFIN 2012
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