Platinum‐Free Counter Electrode Using Polymer‐Capped Graphene Nanoplatelets for Cobalt(II)/(III)‐Mediated Porphyrin‐Sensitized Solar Cells

Abstract

We present a facile and scalable method to prepare water‐dispersed polyvinylpyrrolidone‐capped graphene (PVP‐graphene) nanoplatelets from an ordinary graphite powder. The 3 D hydrophobic graphite powder was exfoliated into 2 D hydrophilic PVP‐graphene nanoplatelets by inducing intercalation through the PVP chains and through high‐powered sonication. The nanoplatelets were characterized by using XRD, field‐emission scanning electron microscopy, TEM, Raman spectroscopy, and X‐ray photoelectron spectroscopy, and they were found to be nonoxidative and to have dimensions of a few hundred nanometers. The suitability of PVP‐graphene as a catalyst for a CoII/III redox couple was evaluated by coating the prepared PVP‐graphene nanoplatelets on fluorine‐doped tin oxide glass through a unique two‐step dipping method. The coated nanoplatelets were examined by using electrochemical impedance spectroscopy, UV/Vis spectroscopy, and current–voltage curve analysis, and it was observed that PVP‐graphene exhibited a high catalytic effect because the charge transfer resistance from CoIII to CoII was as low as 1.17 Ω cm2. A porphyrin‐sensitized solar cell with this counter electrode and an efficiency of 8.95 % was demonstrated.