Metal Selenides as Efficient Counter Electrodes for Dye-Sensitized Solar Cells

Abstract

Solar energy is the most abundant renewable energy available to the earth and can meet the energy needs of humankind, but efficient conversion of solar energy to electricity is an urgent issue of scientific research. As the third-generation photovoltaic technology, dye-sensitized solar cells (DSSCs) have gained great attention since the landmark efficiency of ∼7% reported by O'Regan and Grätzel. The most attractive features of DSSCs include low cost, simple manufacturing processes, medium-purity materials, and theoretically high power conversion efficiencies. As one of the key materials in DSSCs, the counter electrode (CE) plays a crucial role in completing the electric circuit by catalyzing the reduction of the oxidized state to the reduced state for a redox couple (e.g., I/I) in the electrolyte at the CE-electrolyte interface. To lower the cost caused by the typically used Pt CE, which restricts the large-scale application because of its low reserves and high price, great effort has been made to develop new CE materials alternative to Pt. A lot of Pt-free electrocatalysts, such as carbon materials, inorganic compounds, conductive polymers, and their composites with good electrocatalytic activity, have been applied as CEs in DSSCs in the past years. Metal selenides have been widely used as electrocatalysts for the oxygen reduction reaction and light-harvesting materials for solar cells. Our group first expanded their applications to the DSSC field by using in situ-grown CoSe nanosheet and NiSe nanoparticle films as CEs. This finding has inspired extensive studies on developing new metal selenides in order to seek more efficient CE materials for low-cost DSSCs, and a lot of meaningful results have been achieved in the past years. In this Account, we summarize recent advances in binary and mutinary metal selenides applied as CEs in DSSCs. The synthetic methods for metal selenides with various morphologies and stoichiometric ratios and deposition methods for CE films are described. We emphasize that the in situ growth method exhibits advantages over other methods for fabricating stable and efficient CEs. We focus on the effect of morphology on the electocatalytic and photovoltaic performance. Application of transparent metal selenide CEs in bifacial DSSCs and the superiority of in situ-grown metal selenide nanosheet fiber CEs used for fiber DSSCs are presented. In addition, we show that metal selenides with a hollow sphere structure can function not only as an efficient electrocatalyst but also as a light-scattering layer. Finally, we present our views on the current challenges and future development of metal selenide CE materials.

Phase‐Engineered Weyl Semi‐Metallic MoxW1‐xTe2 Nanosheets as a Highly Efficient Electrocatalyst for Dye‐Sensitized Solar Cells

“…TMDs with the composition of MX 2 , containing transition metals ( M = Mo or W) and chalcogens ( X = S, Se, or Te), hold covalent bonds within a layer and van der Waals interactions along the layer‐by‐layer stacking . To date, several semiconductive TMDs have been employed as electrocatalysts in the energy conversion systems, such as dye‐sensitized solar cells (DSSC) and hydrogen evolution reactions (HER) . In electrocatalytic reactions, the specific chalcogen ligands and grain boundaries of TMDs were regarded as the active sites (e.g., the bridging and terminal and the apical and unsaturated in MoS 2 ), whose catalytic activities can be improved by utilizing surface engineering strategies to create artificial vacancies/defects on the basal plane of semicondoctor‐based TMD catalysts .…”

Quaternary Iron Nickel Cobalt Selenide as an Efficient Electrocatalyst for Both Quasi‐Solid‐State Dye‐Sensitized Solar Cells and Water Splitting

“…Noble metals and noble metallic compounds (Pt, RuO 2 , IrO 2 ) have favorable electrocatalytic performance in dye‐sensitized solar cells (DSSCs), the hydrogen evolution reaction (HER), and the oxygen evolution reaction (OER) . However, they are expensive and easily deactivated by the chemisorption of corrosive electrolytes (e.g., electrolytes that contain iodine) . Therefore, a lot of effort has been made to develop earth‐abundant electrocatalysts with high catalytic activity and low cost.…”

“…[1] However,t hey are expensive and easily deactivated by the chemisorption of corrosive electrolytes (e.g.,e lectrolytes that contain iodine). [2] Therefore, al ot of effort has been made to develop earth-abundant electrocatalysts with high catalytic activity and low cost. Metal chalcogenides, such as MoSe, CoS, Co 0.85 Se, Ni 0.85 Se, NiCo 2 Se 4 , and Co-Fe-Se, have been reported to show high catalytic activity in DSSCs, HER, OER, and overall water splitting.…”

A review on applications of Cu2ZnSnS4 as alternative counter electrodes in dye-sensitized solar cells

“…Superior catalytic activity, flexible electrochemical performance, good conductivity, high active area, cheaper and greener synthesis and fabrication techniques, effective performance is expected from CE alternative to Pt in DSSC. Recently graphene and other carbon based composites, [37][38][39] 44,45 exhibited performance that is competitive to Pt. The research has led to large increasing number of publications.…”