Sulfur‐Doped Nickel Oxide Thin Film as an Alternative to Pt for Dye‐Sensitized Solar Cell Counter Electrodes

Abstract

Dye-sensitized solar cells (DSSCs) have attracted intense research attention because of their low cost and high efficiency in converting solar energy into electricity. [1,2] Typically, a DSSC constitutes a dye-loaded mesoporous TiO 2 photoelectrode, an electrolyte containing iodide/tri-iodide (I − /I 3 − ) redox couples, and a catalytic counter electrode which reduces I 3 − ions. [3,4] Since both the photo and counter electrodes are exposed to the electrolyte, a high DSSC performance is greatly dependent on a fast reduction reaction at the counter electrode to suppress the possible reduction reaction by a charge recombination process at the photoelectrode. [5,6] To achieve such selectivity, noble platinum (Pt) is often used as a catalyst on fluorine-doped tin oxide (FTO) conducting glass to enhance the reduction rate at the counter electrode. [7] However, Pt is expensive and non-sustainable for long-term applications. Carbon-based materials such as polymers, carbon black, and carbon nanotubes have also been reported to replace Pt catalysts. [8,9] However, these carbon materials have much weaker catalytic activities than Pt and thus require large carbon loadings (loading ∼300 to >1000 μg cm −2 ) to compensate for the lowered electrocatalytic activity, resulting in poor device energy density. [9][10][11] Therefore, a low cost and robust alternative counter electrode with high electrocatalytic activity towards I 3 − reduction is in high demand. Transition metal based materials have been demonstrated to possess outstanding catalytic performance in redox reactions because of their multiple oxidation states. [12,13] However, very few of such materials have been studied and employed as a DSSC counter electrode. [14,15] In this study, nickel oxide (NiO) is selected as a potential electrode material because of its good charge capacity, [16] high chemical stability, [17,18] and a valence band energy (∼-4.96 eV) comparable to the redox potential of I − /I 3 − for favorable charge transfer between the metal oxide and redox couples, [19,20] although its low conductivity and poor charge carrier mobility limit its actual charge transfer process. To improve the charge transfer impedance of NiO, a sulfur-doped nickel oxide (S-NiO) thin film is fabricated for a DSSC counter electrode and its electrocatalytic activity towards the I − /I 3 − redox process is investigated. By using an electrophoretic deposition method, a porous S-NiO thin film with a nanorod-like network is fabricated on a FTO substrate to greatly enhance its effective reaction surface area. The surface composition and morphology of the S-NiO thin film are characterized using scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and energy dispersive spectroscopy (EDS). The results obtained from cyclic voltammetry (CV) and alternating current (A.C.) impedance measurements indicate that the S-NiO\FTO (SNO) electrode possesses high electrocatalytic activity towards the I − /I 3 − redox process as compared to both plain NiO\FTO (NO) and FTO electro...

Sandwich-like octahedral cobalt disulfide/reduced graphene oxide as an efficient Pt-free electrocatalyst for high-performance dye-sensitized solar cells

“…In addition, the sandwich-like CoS 2 /RGO-20 CE possesses a smaller E pp , which means efficiently lowered overpotential and improved catalytic reaction rate in the reduction of triiodide to iodide [50]. The high reduction peak current and low E pp demonstrate the synergistic effects between CoS 2 and graphene, and further confirm and nonuniform morphology of CoS 2 nanoparticles (Fig.…”

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

“…The peaks at ∼860.6 and ∼878.9 eV were due to the satellite peaks of 2p3/2 and 2p1/2 peaks of Ni 2+ , respectively. 39 In addition, a weak splitting peak of Ni 2p3/2 peak was also observable at ∼855.3 eV, which is due to the presence of oxidation state of Ni 3+ . 40,41 But the above XRD measurements show that no any other impurity phases were observed in all annealed samples within the detection limit of X-ray diffractometer.…”

Review on the recent progress of carbon counter electrodes for dye-sensitized solar cells

“…Currently, the hot issues are to seek for the economical and highly catalytic materials to replace Pt for the sustainable development. Several varieties of low-cost candidates, such as carbonaceous materials [20][21][22][23][24][25], conductive polymers [26][27][28][29], alloys [30], metal oxide [31,32], transition metal based materials including metal carbides [33], metal nitrides [34][35][36][37], and metal sulfides [38][39][40] have 3 been widely investigated as novel counter electrode alternatives and demonstrated outstanding catalytic performance for the triiodide reduction. In particular, carbonaceous materials such as graphite, carbon black, activated carbon, mesoporous carbon, carbon nanotubes and fullerenes have attract more attention compared to other counter electrode materials, due to their relatively low cost, good stability, and high catalytic ability [41][42][43][44].…”