Plastic based dye-sensitized solar cells using Co9S8 acicular nanotube arrays as the counter electrode

Novel one-dimensional (1D) Co9S8 acicular nanotube arrays (ANTAs) are fabricated on a conducting plastic substrate by a two-step approach. Layered cobalt carbonate hydroxide (Co(CO3)(0.5)(OH)(x)center dot 11H(2)O, LCCH) acicular nanorod arrays (ANRAs) are fabricated on a conducting plastic substrate by chemical bath deposition (CBD), followed by a simple ionic-exchange process to convert the LCCH ANRAs into Co9S8 ANTAs. The compositions of the films are verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) mapping; their morphologies are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The films of Co9S8 ANTAs, obtained after various periods of the CBD, are analyzed by cyclic voltammetry (CV) measurements and Tafel polarization curves, and the Co9S8 ANTAs obtained from 150 min of CBD show higher electrocatalytic ability towards the I-/I-3(-) reaction than sputtered Pt. In addition, the long-term stability of the Co9S8 ANTAs film in I-/I-3(-) electrolyte was tested by CV. The plastic based Co9S8 ANTAs electrodes are used as the counter electrodes (CEs) of flexible dye-sensitized solar cells (DSSCs), and a high power conversion efficiency of 5.47% is achieved, which is comparable to that of the DSSC using sputtered Pt (5.62%). Therefore, the Co9S8 ANTAs are proposed to be a reliable material to replace Pt as plastic based CEs of DSSCs.