Tailoring Polymorphic CoSe2 via Interstitial Doping of Sb for Advanced Counter Electrodes in DSSC applications

The counter electrode (CE) layer in dye-sensitized solar cells (DSSCs) acts as a cornerstone in the catalytic reduction of the redox electrolyte, typically the iodide/triiodide (I⁻/I₃⁻) redox electrolyte couple, and facilitates the replenishment of the oxidized dye molecules. The substantial cost, sparse availability, and proneness to corrosion of conventionally used Platinum (Pt) CE with the I⁻/I₃⁻ electrolyte, have spurred extensive research into alternative CE materials. Transition metal dichalcogenides (TMDs), especially cobalt diselenide (CoSe₂), have emerged as potential substitutes for CE material in DSSC due to their good electrochemical properties and high conductivity. This study focuses on the potential of antimony (Sb)-doped CoSe₂ as a novel material for CE application in DSSC, aiming to improve the stability, electrocatalytic activity, and overall device performance. We prepared Sb-doped CoSe₂ with various doping concentrations using a simple hydrothermal technique and analysed the compositional, morphological and structural properties of the prepared materials. The CoSe₂ doped with 4 wt% Sb (4Sb-CoSe₂) exhibited enhanced charge transfer kinetics, low charge transfer resistance, and superior catalytic activity compared to other concentrations, making it comparable to standard Pt CE in electrochemical analysis. DSSC fabricated with 4Sb-CoSe₂ CE achieved a photovoltaic (PV) efficiency of 6.99% under AM 1.5G, which is attributed to the interstitial doping of Sb³⁺ ions, that increases the active sites for redox processes, conductivity and charge transport kinetics of CE. The 16-day stability assessment reveals that the 4Sb-CoSe₂-based DSSC retains stable PV performance with only minor efficiency loss, indicating strong durability against the iodide/triiodide redox electrolyte. Therefore, Sb-doped CoSe₂ can be a viable substitute for Pt CE in DSSC and can be utilised for their large-scale production.