Insight into the topological defects and dopants in metal-free holey graphene for triiodide reduction in dye-sensitized solar cells

Exploiting highly active and stable counter electrodes (CEs) has been a persistent challenge for the practical application of dye-sensitized solar cells (DSSCs). Herein, we present an edge-enhanced modification to fabricate nitrogen doped holey graphene (NHG) by rationally employing N-2 plasma treatment at the exposed edge sites of holey graphene. The as-synthesized NHG exhibits a highly conductive and unique holey scaffold with a large surface area, along with abundant edge-induced topological defects and nitrogen dopants. Benefiting from such unique features, NHG exhibits outstanding electrocatalytic activity and high electrochemical stability for the I-/I-3(-) redox reaction. Furthermore, density functional theory calculations are performed to further elucidate the underlying mechanism behind this encouraging performance, in particular the effect of edge-induced topological defects. The DSSCs based on NHG CEs display a power conversion efficiency of 9.07%, which is even superior to that of Pt (8.19%). These results strongly indicate possibilities for the large-scale fabrication of low-cost and metalfree NHG materials for DSSCs with an I-complex redox couple.