Novel 2D-AuSe nanostructures as effective platinum replacement counter electrodes in dye-sensitized solar cells

Studies to improve the efficiency of dye-sensitized solar cells (DSSCs) include, but are not limited to, finding alternatives such as 2D layered materials as replacement counter electrodes (CEs) to the commonly used Pt. Herein, we report for the first time, the use of AuSe as a counter electrode for the reduction of triiodide ions (I-3(-)) to iodide ions (I-). The colloidal synthesis of gold selenide nanostructures produced alpha-AuSe and beta-AuSe dominated products as determined by XRD. Electron microscopy showed alpha-AuSe having belt-like structures while beta-AuSe had a plate-like morphology. EDS mapping confirmed the elemental composition and homogeneity of the AuSe CEs. Cyclic voltammetry curves of the AuSe CEs displayed the double set of reduction-oxidation peaks associated with the reactions in the I-3(-)/I- electrolyte and therefore were comparable to the Pt CV curve. The alpha-AuSe CE showed better electrocatalytic activity with a reduction current of 6.1 mA than that of beta-AuSe and Pt CEs, which were 4.2 mA and 4.8 mA, respectively. The peak-to-peak separation (Delta E-pp) for the alpha-AuSe CE was also more favourable with a value of 532 mV over that of the beta-AuSe CE of 739 mV however, both values were larger than that of the Pt CE, which was found to be 468 mV. The EIS and Tafel plot data showed that alpha-AuSe had the best catalytic activity compared to beta-AuSe and was comparable to Pt. The DSSC using alpha-AuSe as a CE had the highest PCE (6.94%) as compared to Pt (4.89%) and beta-AuSe (3.47%). The lower efficiency for Pt was attributed to the poorer fill factor. With these novel results, alpha-AuSe is an excellent candidate to be used as an alternative CE to Pt in DSSCs.