Journal of Energy Chemistry 24 (2015) 762–769 http://www.journals.elsevier.com/ journal-of-energy-chemistry/ Contents lists available at ScienceDirect Journal of Energy Chemistry journal homepage: www.elsevier.com/locate/jechem Facile fabrication of TiO 2 nanoparticle–TiO 2 nanofiber composites by co-electrospinning–electrospraying for dye-sensitized solar cells ✩ G. S. Anjusree, T. G. Deepak, Shantikumar V Nair, A. Sreekumaran Nair ∗ Nanosolar Division, Amrita Centre for Nanosciences & Molecular Medicine, Amrita Institute of Medical Sciences (AIMS), Amrita Vishwa Vidyapeetham University, AIMS PO, Ponekkara, Kochi 682041, Kerala, India article info Article history: Received 31 July 2015 Revised 25 August 2015 Accepted 13 October 2015 Available online 5 November 2015 Keywords: TiO 2 nanofiber–nanoparticle composites Co-electrospraying–electrospinning Dye-sensitized solar cell Current–voltage measurements abstract We report a facile method for the fabrication of TiO 2 nanofiber–nanoparticle composite (FP) via. simulta- neous electrospraying and electrospinning for dye-sensitized solar cell (DSC) applications. The loading of nanoparticles on the fibers is controlled by varying their feed rates during electrospinning. The FP compos- ites having three different particle loading are prepared by the methodology and the FP with the highest particle loading (denoted as FP-3 in the manuscript) showed the best overall efficiency of 9.15% in compar- ison to the other compositions of the FP (FP-2, 8.15% and FP-1, 7.51%, respectively) and nanofibers (F) and nanoparticles (P) separately (7.21 and 7.81, respectively). All the material systems are characterized by spec- troscopy, microscopy, surface area measurements and the devices are characterized by current–voltage (I-V), incident photon-to-current conversion efficiency (IPCE), electrochemical impedance measurements, etc. I-V, dye-loading and reflectance measurements throw light on the overall performance of the DSC devices. © 2015 Science Press and Dalian Institute of Chemical Physics. All rights reserved. 1. Introduction Dye-sensitized solar cell [1] (DSC) is a promising technology for renewable energy owing to its relatively inexpensive materials and simple fabrication processes involved. In a typical DSC, the photoan- ode is composed of a film of sintered mesoporous TiO 2 nanoparticles sensitized with a dye. Upon band-gap excitation, electrons from the dye molecules are excited and subsequently injected into the con- duction band of TiO 2 and then transported (by diffusion) through the mesoporous TiO 2 film to the front electrode (the fluorine-doped tin oxide, FTO). The electrons are collected at the counter electrode through an external load and shuttled back to the oxidized dye molecules via reactions with I − /I 3− redox couple in the electrolyte [2]. The important parameters responsible for high photoelectric con- version efficiency of DSCs are the light harvesting efficiency of the dye, the efficiency of electron transfer from the excited dye molecules to the photoanode (depends on the effective chemical conjugation of the dye and the TiO 2 ) and the charge transport through the photoan- ode [3]. The conventional photoanode made of TiO 2 nanoparticles (10–30 nm) are beneficial for good mass loading of TiO 2 (because of their high packing density) and hence high dye-loading but inferior in light scattering due to their smaller sizes compared to the wavelength ✩ This work was supported by Ministry of New and Renewable Energy (MNRE) and the Solar Energy Research Initiative (SERI), respectively, of Govt. of India. ∗ Corresponding author. Tel: +91 484 12345643. E-mail address: sreekumarannair@aims.amrita.edu (A.S. Nair). of the incident light [4]. Moreover, the photoanode film made of poly- crystalline TiO 2 nanoparticles usually have a large number of struc- tural defects (such as dead-ends in the array of their films, crystal de- fects, etc.) and grain boundaries (being polycrystalline) which would introduce surface trap sites for recombination in the conduction band of TiO 2 [5]. The trapping and de-trapping of electrons occurring dur- ing the electron diffusion process become a limiting factor for charge collection in DSCs. There are chances that the electrons trapped in the surface traps recombine with the I 3− in the electrolyte thus increas- ing the interfacial charge recombination [6,8]. In order to improve the charge collection efficiency of a DSC, considerable research has been done on 1-D (one-dimensional) nanomaterials such as nanofibers [9,10], nanowires [11,12], nanorods [13,14], nanotubes [15,16], which contain a lesser number of recombination centers thus providing di- rectional channels for electron transport. Though these nanostruc- tures provide good light scattering property mostly in the red part of the solar spectrum, the internal surface areas of these nanostruc- tures are lower than that of the nanoparticles thus resulting in lower dye-loading and hence lower efficiency for the devices. Hence, the light harvesting and overall device efficiency were limited in the DSCs based on 1-D nanostructures [17,18]. Thus, we thought of fabricat- ing a single nanoarchitecture, which combines the advantages of 1-D TiO 2 nanofibers and 0-D TiO 2 nanoparticles such as good light scat- tering, dye loading. We have recently reported a communication on a unique 1-D morphology of TiO 2 having TiO 2 nanoparticles deco- rating the surface of TiO 2 nanofibers fabricated by a simultaneous electrospinning and electrospraying technique [19]. The composite http://dx.doi.org/10.1016/j.jechem.2015.11.001 2095-4956/© 2015 Science Press and Dalian Institute of Chemical Physics. All rights reserved.