Nitrogen and phosphorus dual-doped graphene as a metal-free high-efficiency electrocatalyst for triiodide reduction

Alternative high-performance electrocatalysts for triiodide (I₃^-) reduction of low-cost dye-sensitized solar cells (DSSCs) are urgently sought after. To address the concerned issues, we report a facile strategy for engineering the nitrogen and phosphorus dual-doped graphene (NPG) via an efficient ball-milling process, followed by a simple thermal annealing approach utilizing melamine (C₃H₆N₆) and triphenylphosphine ((C₆H₅)₃P) as the N and P source, respectively. When employed as the counter electrode (CE) in DSSCs, such a metal-free material exhibits excellent electrocatalytic activity towards the I₃^-/I^- redox reaction. Dual-doping of N and P heteroatoms can markedly enhance the photovoltaic performance of DSSCs by a synergistic effect and a high conversion efficiency of 8.57% is achieved, which is superior to Pt CE, and much higher than that of the single-component N- or P-doped graphene electrodes. In addition, the NPG CE also shows an outstanding electrochemical stability. The present results demonstrate that the NPG as a low-cost and high-efficiency electrocatalyst for reduction of I₃^- will be one of the promising CE materials in DSSCs.