Interconnected nitrogen and sulfur co-doped graphene-like porous carbon nanosheets with high electrocatalytic activity as counter electrodes for dye-sensitized and quantum dot-sensitized solar cells

Interconnected nitrogen and sulfur co-doped graphene-like porous carbon nanosheets (NSGPCSs) are facilely produced by thermal annealing methyl orange (MO) doped polypyrrole (PPy) nanotubes at the presence of KOH under N2 atmosphere at 700 °C. The pyrolysis of PPy combined with the dedoping of PPy nanotubes derived from the interactions between KOH and MO lead to transforming 1D PPy nanotubes into 2D graphene-like carbon nanosheets. The as-prepared NSGPCSs have high specific surface area (up to 1744.98 m2 g−1) and hierarchical porosity, and are investigated as the counter electrodes for dye-sensitized and quantum dot-sensitized solar cells. The unique characteristics such as co-doping of nitrogen and sulfur heteroatoms, high specific surface area, and interconnected graphene-like nanosheets with hierarchical porosity render NSGPCSs a promising electrode material for photoelectrochemical cells. Electrochemical investigations indicate that NSGPCS electrodes display excellent electrocatalytic activity for the regeneration of the I−/I3− and polysulfide electrolytes. As a result, the dye-sensitized solar cell based on NSGPCS electrode achieves a conversion efficiency of 8.21%, which is very close to that of the cell based on conventional Pt electrode (8.61%). The efficiency of the quantum dot-sensitized solar cell assembled with NSGPCS counter electrode is significantly higher than that of the cell assembled with Pt counter electrode, and comparable to that of the cell assembled with PbS counter electrode.