Fabrication of well-arrayed plasmonic mesoporous TiO2/Ag films for dye-sensitized solar cells by multiple-step nanoimprint lithography

Abstract

This paper presents a photo-anode with well-arrayed plasmonic mesoporous TiO₂/Ag films for plasmon enhanced dye-sensitized solar cells. The patterned mesoporous TiO₂ nanostructure was implemented by multiple-step nanoimprint lithography (NIL), which can generate complex micro/nanostructures by successive imprinting on the same area using a combination of simpler flexible templates. Ag nanoparticles were introduced into the TiO₂ network by the photoreduction process to excite the plasmonic effect. Moreover, the morphological, material, optical and electrochemical properties of the patterned mesoporous TiO₂/Ag films were investigated by scanning electron microscopy, transmission electron microscopy, X-ray analysis, UV-Vis absorption spectroscopy and electrochemical impedance spectroscopy. The energy conversion efficiency and photocurrent density for patterned TiO₂/Ag cells were enhanced by about 24% and 25% as compared with those of the pure TiO₂ cells. The experimental observations demonstrate that the plasmonic effect can be enhanced by periodic patterns, allowing more broad light waves to couple to plasmonic wavelength due to the multiple reflection of incident light. The results also indicate that applying the multiple-step NIL process can not only increase the surface area of the photo-anode but also enhance the adherence at the TiO₂/TiO₂ nanoparticle interface and TiO₂/conductive substrate interface improving the electrochemical properties. With its simplicity and time-saving options, this method of fabricating patterned electrodes can be widely applied to a variety of large-area thin film solar cells.