Synergistic performance of Ternary Ni_1 − xFe_xSe₂ octahedrons as a platinum-free counter electrode catalyst for enhanced triiodide reduction in dye-sensitized solar cells

This study explores the impact of Fe doping on the NiSe₂ structure synthesized via a straightforward hydrothermal method, aiming to utilize the Fe-doped NiSe₂ as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). X-ray diffraction (XRD) patterns confirmed the formation of a cubic NiSe₂ crystal structure. Notably, increasing Fe doping concentrations in NiSe₂ resulted in a peak shift towards higher angles, attributable to the smaller ionic radius of Fe³⁺ (0.64 Å) compared to Ni²⁺ (0.69 Å). Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed the formation of octahedron-like morphologies. The electrocatalytic performance internal resistance and charge transfer kinetics of NiSe₂, Ni_0.97Fe_0.03Se₂, Ni_0.94Fe_0.06Se₂, Ni_0.91Fe_0.09Se₂, and Ni_0.88Fe_0.12Se₂, in comparison to platinum (Pt), was evaluated through cyclic voltammetry (CV) and Tafel polarization and Electrochemical impedance spectroscopy (EIS) analysis. From the CV analysis, the Ni_0.91Fe_0.09Se₂ electrode demonstrated the highest anodic and cathodic peak current densities (I_p.a. and I_pc) and the lowest peak potential (E_pp), indicating superior catalytic activity. EIS results further revealed that the Ni_0.91Fe_0.09Se₂ electrode had the lowest series resistance (R_s) and charge transfer resistance (R_ct) compared to Pt and other electrodes, suggesting more efficient charge transfer. Additionally, Tafel analysis showed that the Ni_0.91Fe_0.09Se₂ electrode exhibited the highest exchange current density (J₀) and the highest limiting diffusion current (J_lim), which further confirms its enhanced catalytic performance. The prepared samples were coated on fluorine-doped tin oxide (FTO) substrates using the doctor-blade method and integrated into DSSCs with a titanium dioxide (TiO₂) photoanode. The efficiencies of DSSCs using CEs of NiSe₂, Ni_0.97Fe_0.03Se₂, Ni_0.94Fe_0.06Se₂, Ni_0.91Fe_0.09Se₂, and Ni_0.88Fe_0.12Se₂, and Pt were 5.28 ± 0.14%, 5.83 ± 0.14%, 6.03 ± 0.11%, 7.02 ± 0.39%, 6.40 ± 0.16%, and 5.95 ± 0.07%, respectively. The DSSC with the Ni_0.91Fe_0.09Se₂ CE demonstrated the highest efficiency, surpassing Pt and other CEs, indicating its potential for developing high-performance DSSCs. This advancement supports the progress of sustainable and renewable energy technologies.