Improved electrocatalytic activity of electrodeposited Ni3S4 counter electrodes for dye- and quantum dot-sensitized solar cells

Abstract Nickel sulfide (Ni 3 S 4 ) films are deposited onto F-doped SnO 2 (FTO) substrates using a facile one-step potentiodynamic electrodeposition without any extra treatment. The potential sweep is between −0.9 V and 0.7 V (vs. Ag/AgCl) for 4–10 cycles. The series resistance is gradually reduced with increased Ni 3 S 4 film thickness, indicating the metallic conduction of the Ni 3 S 4 phase. The Ni 3 S 4 deposited for 8 cycles (denoted FTO/Ni 3 S 4 -8) exhibits full coverage on the FTO substrate, with 110 nm thickness and a distinctive structure of porous and nanoscale interconnecting nanoparticular networks, which provide numerous electrochemical active sites to contact with electrolyte. The film not only exhibits prominent electrocatalytic activities but also shows excellent electrochemical stability in both polysulfide and iodide-based electrolytes compared to FTO/Pt. On the contrary, the FTO/Ni 3 S 4 -10 shows merged clusters, leading to more compact and less porous morphology, which reduced electrocatalytic activity. The quantum dot-sensitized solar cell (QD-SSC) fabricated using the FTO/Ni 3 S 4 -8 counter electrode (CE) exhibits power conversion efficiency (PCE) of 4.57%, short-circuit current (J sc ) of 15.92 mA cm −2 , open-circuit voltage (V oc ) of 0.545 V, and fill factor (FF) of 52.63%. In addition, the dye-sensitized solar cell (D-SSC) using FTO/Ni 3 S 4 -8 CE achieves a PCE of 8.17%, J sc of 16.28 mA cm −2 , V oc of 0.735 V, and FF of 68.34%. On the other hand, the PCEs of 2.56% and 7.58% are obtained for QD-SSC and D-SSC with Pt CE, respectively. We suggest that the electrodeposited Ni 3 S 4 should be promising electrocatalytic electrodes for various applications such as QD-SSCs, D-SSCs, supercapacitors, photoelectrochemical water-splitting cells, and batteries.