Electrospun TiO 2 nanowires for hybrid photovoltaic cells
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A simple and controllable fabrication of TiO2 nanowires by electrospinning and their applications to the electron transporting layer for hybrid organic–inorganic photovoltaic cells are reported. TiO2 nanowires were directly electrospun onto an indium tin oxide on glass substrate from a solution in methanol of polyvinylpyrrolidone, titanium(IV) butoxide, and acetylacetone. The nanowire electrode obtained was consequently subjected to calcination at 450 °C. Solution of blended [6,6]-phenyl-C61-butyric acid methyl ester and poly(3-hexylthiophene) was spin coated on the TiO2 nanowire electrode, followed by thermal annealing and deposition of Au electrode. Hybrid organic–inorganic photovoltaic cells made of TiO2 nanowires exhibited remarkable improvement of the cell efficiencies in terms of photocurrent density and open-circuit voltage as compared with those of references, TiO2 flat films. Maximum energy conversion efficiency of hybrid organic–inorganic photovoltaic cells made of TiO2 nanowires of 1.27% was achieved.
I. INTRODUCTION
Recently, polymer-based organic photovoltaic cells have attracted a great interest in terms of lightweight, printable, and flexible photovoltaic devices.1,2 Typically, conjugated low band gap polymer (electron donor) is blended with an electron accepter to achieve a bulk heterojunction layer. In this system, photons are absorbed by the electron donor, then excitons are generated, diffuse to the interface of the two bulk components, and dissociate. The acceptor receives the electron and transfers to the electrode while the hole remains within the donor. The highpower conversion efficiencies (4–5%) have been reported, which focused on regioregular poly(3-hexylthiophene) 6,6 (P3HT, as donor) and -phenyl-C61-butyric acid methyl ester (PCBM, as acceptor).3–5 However, in comparison to typical inorganic photovoltaic cells, the power conversion efficiencies of reported organic photovoltaic devices are still very low. Such evidence can be attributed to the low stability of the organic material, inconsistency between the solar and polymer absorption spectrum, and especially the low mobility of excited electron or hole.6 To improve the cell efficiencies, the combination of organic and inorganic semiconductor as hybrid organic–inorganic photovoltaic cells has been extremely investigated to overcome the low mobility of carriers by using nanostructured inorganic materials as electron transporting layers.7–12 One-dimensional (1D) nanostructured metal oxides are promising electrodes for photovoltaic devices due to their high conductivity as a direct path for charge transport.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.167 2316
J. Mater. Res., Vol. 26, No. 17, Sep 14, 2011
http://journals.cambridge.org
Downloaded: 30 Apr 2015
Among these various nanostructured metal oxides, TiO2 is an attractive oxide because of its processability and appropriate band gap.13 In our previous works, we reported the fabrication of TiO2 nanowires (also called nanofibers)
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