Yudi Wang

Economical Pt-Free Catalysts for Counter Electrodes of Dye-Sensitized Solar Cells

Three classes (carbides, nitrides and oxides) of nanoscaled early-transition-metal catalysts have been proposed to replace the expensive Pt catalyst as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). Of these catalysts, Cr(3)C(2), CrN, VC(N), VN, TiC, TiC(N), TiN, and V(2)O(3) all showed excellent catalytic activity for the reduction of I(3)(-) to I(-) in the electrolyte. Further, VC embedded in mesoporous carbon (VC-MC) was prepared through in situ synthesis. The I(3)(-)/I(-) DSC based on the VC-MC CE reached a high power conversion efficiency (PCE) of 7.63%, comparable to the photovoltaic performance of the DSC using a Pt CE (7.50%). In addition, the carbide catalysts demonstrated catalytic activity higher than that of Pt for the regeneration of a new organic redox couple of T(2)/T(-). The T(2)/T(-) DSCs using TiC and VC-MC CEs showed PCEs of 4.96 and 5.15%, much higher than that of the DSC using a Pt CE (3.66%). This work expands the list of potential CE catalysts, which can help reduce the cost of DSCs and thereby encourage their fundamental research and commercial application.

Economical and effective sulfide catalysts for dye-sensitized solar cells as counter electrodes

Molybdenum sulfide (MoS(2)) and tungsten sulfide (WS(2)) are proposed as counter electrode (CE) catalysts in a I(3)(-)/I(-) and T(2)/T(-) based dye-sensitized solar cells (DSCs) system. The I(3)(-)/I(-) based DSCs using MoS(2) and WS(2) CEs achieved power conversion efficiencies of 7.59% and 7.73%, respectively.

Novel counter electrode catalysts of niobium oxides supersede Pt for dye-sensitized solar cells.

Synthesized niobium oxides (Nb(2)O(5) and NbO(2)) were applied for the first time as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). The DSC using NbO(2) CE showed a higher power conversion efficiency of 7.88%, compared with that of the DSC using Pt CE (7.65%).

Pt‐like Behavior of High‐Performance Counter Electrodes Prepared from Binary Tantalum Compounds Showing High Electrocatalytic Activity for Dye‐Sensitized Solar Cells

Ta-based compounds show Pt-like behavior: Binary tantalum compounds as counter electrodes (CEs) in dye-sensitized solar cells (DSCs) demonstrate Pt-like electrocatalytic activity and competitive photovoltaic performance, matching the performance of DSCs with Pt CEs. The first-principle density functional theory (DFT) calculations provide a strategy for understanding the relationship between the electronic structure and the catalytic activity of CE catalysts in DSCs.

One-step synthesis of nano-scaled tungsten oxides and carbides for dye-sensitized solar cells as counter electrode catalysts

Nano-scaled tungsten oxides and carbides are synthesized using a simple one-step chemical method. They are subsequently introduced into dye-sensitized solar cells (DSCs) as counter electrode (CE) catalysts to replace the expensive Pt. The catalytic mechanism is investigated by measurements of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel-polarization curve for the as-prepared catalysts. The DSCs using WC/W2C, W2C and WO2 as CE catalysts yield high power conversion efficiency (PCE) of 6.23%, 6.68%, and 6.88%, respectively, comparable to that of the DSC using Pt CE. The results demonstrate that tungsten oxides and carbides are the potential alternative to the expensive Pt CE for reducing the cost of DSCs.

Counter electrode materials combined with redox couples in dye- and quantum dot-sensitized solar cells

Dye- or quantum dot-sensitized solar cells (DSCs or QDSCs) comprise a sensitizer, a semiconductor, an electrolyte containing redox couple, and a counter electrode (CE), which have inspired a new wave of research. The challenges in realizing the practical application of such photovoltaic devices are the enhancement of photovoltaic performance, stability, and the reduction of fabrication costs. The CE is an important component, and the exploration of low cost CE catalysts to match the redox couples has become a feasible route in the pursuit of high power conversion efficiency and low production cost of the devices. This article reviews the development of CE catalysts for the regeneration of each type of iodide-free redox couple, including inorganic, organic, and transition metal complex-based redox couples, among others.

Transparent flexible Pt counter electrodes for high performance dye-sensitized solar cells

A transparent flexible Pt counter electrode (CE) was prepared on indium tin oxide–polyethylene naphthalate film using a simple dip coating method for dye-sensitized solar cells (DSCs), and a high catalytic activity was achieved. The DSC using this transparent flexible CE gave a power conversion efficiency (PCE) of 6.95% with front illumination, and a PCE of 5.18% with rear illumination.

TiC/Pt composite catalyst as counter electrode for dye-sensitized solar cells with long-term stability and high efficiency

Titanium carbide/platinum (TiC/Pt) composites were prepared by a simple chemical route and subsequently introduced into dye-sensitized solar cells (DSCs) as counter electrode (CE) catalysts to improve the catalytic activity and reduce the cost of DSCs. The DSC using TiC/Pt (containing 0.12 wt% of Pt) CE showed high power conversion efficiency (PCE) of 7.63%, higher than those of DSCs using TiC and Pt CEs (6.40% and 7.16%, respectively). After a long-term (one year) stability test, the PCE of the DSC using this CE retained 86.9% of its highest value, proving the outstanding durability of the TiC/Pt composite. In large-scale DSCs (55 mm × 75 mm), the DSC using TiC/Pt CE yielded a PCE of 4.98%, comparable to that of a DSC using Pt CE (4.94%). This work points out the feasibility of using TiC/Pt composite CEs in practical applications.

Printable fabrication of Pt-and-ITO free counter electrodes for completely flexible quasi-solid dye-sensitized solar cells

Low-cost bendable photoanodes and counter electrodes (CEs), as well as gel electrolytes, are potentially desired for the mass production of completely flexible dye-sensitized solar cells (DSSCs). In this work, via printing at low temperature, we fabricated titanium carbide (TiC)-functionalized conductive-carbon (CC) on flexible polyimide (PI) films to replace traditional and expensive Pt/ITO/PEN CEs. Morphology characterization revealed this composite CE was highly porous and homogeneous. Electrochemical investigations demonstrated that this Pt-and-ITO free flexible CE exhibited a high electro-catalytic activity. Finally, the conversion efficiencies of the all flexible quasi-solid DSSCs using this low-cost TiC-CC/PI CE achieved 86% of that based on a Pt/CC/PI CE. Thus, the facile fabrication process of this novel CE, along with its notable performance, are quite promising for the future roll-to-roll production of completely flexible DSSCs.

An Autocatalytic Factor in the Loss of Efficiency in Dye-Sensitized Solar Cells

We propose a passive factor, autocatalytic activity of some semiconductors (SnO2, WO3), for the loss of efficiency in dye-sensitized solar cells. On one hand, in the photoanode, SnO2 (or WO3) functions as a semiconductor to collect the photoelectrons that are generated by the sensitizer. On the other hand, SnO2 (or WO3) can also work as a catalyst to catalyze the recombination between the photoelectrons and the I3- ions, which results in a large current leakage, a low open-circuit voltage value, and a low efficiency. Some oxides, including, but not limited to, SnO2 and WO3, which have catalytic activity for I3- redn. or other oxidized species of the electrolyte are not suitable for use as semiconductor for the photoanode. In addn. to the semiconductors, phthalocyanine dyes also have catalytic activity for the recombination.