N-Doped Hierarchical Hollow Mesoporous Carbon as Metal-Free Cathode for Dye-Sensitized Solar Cells

In this study, novel nitrogen (N)-doped hollow core-mesoporous shell carbon (N-HCMSC) capsules with high surface area are synthesized by simple three-step processes and explored as metal-free counter electrode (CE) in comparison with undoped HCMSC in dye-sensitized solar cells (DSSCs). It is shown that N-HCMSC significantly improves the catalytic activity toward the reduction of both Co(bpy)33+ and I3– due to much lower charge-transfer resistance (RCT) at the CE/electrolyte interface. This is attributed not only to excellent surface properties including three-dimensionally interconnected hierarchical marco/mesoporosity with high surface area but also to N doping in N-HCMSC framework. Among various N species in the N-HCMSC framework, pyridinic and quaternary N species are considered to contribute significantly to the catalytic activity. In addition, N-HCMSC CE exhibits much better electrochemical stability than Pt CE toward both Co(bpy)32+/3+ and I–/I3– redox reactions. The N-HCMSC enhances the cell effici...