Tingli Ma

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.

Low‐Cost Molybdenum Carbide and Tungsten Carbide Counter Electrodes for Dye‐Sensitized Solar Cells

Carbide-based catalysts, MoC and WC embedded in ordered nanomesoporous carbon were developed for the redn. of triiodide in DSSCs. CV, EIS, Tafel polarization, and photocurrent/voltage tests confirm the excellent catalytic activity of the synthesized carbide-based composites - comparable to that of expensive Pt catalyst prepd. through pyrolysis. Com. Mo2C and WC particles also effectively catalyze the redn. of triiodide to iodide despite their large particle size. The results show that the addn. of P25 and CD (carbon dye) improves the adhesion, the catalytic activity and the cond. of Mo2C and WC electrodes. The optimum amts. of added P25 and CD added were also detd. Results demonstrate that molybdenum and tungsten carbides are potential alternatives to the expensive and scarce Pt in low-cost DSSCs.

CH3NH3SnxPb(1–x)I3 Perovskite Solar Cells Covering up to 1060 nm

We report photovoltaic performances of all-solid state Sn/Pb halide-based perovskite solar cells. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/CH3NH3SnxPb(1-x)I3/regioregular poly(3-hexylthiophene-2,5-diyl). Sn halide perovskite itself did not show photovoltaic properties. Photovoltaic properties were observed when PbI2 was added in SnI2. The best performance was obtained by using CH3NH3Sn0.5Pb0.5I3 perovskite. 4.18% efficiency with open circuit voltage 0.42 V, fill factor 0.50, and short circuit current 20.04 mA/cm(2) are reported. The edge of the incident photon to current efficiency curve reached 1060 nm, which was 260 nm red-shifted compared with that of CH3NH3PbI3 perovskite solar cells.

Low-cost dye-sensitized solar cell based on nine kinds of carbon counter electrodes

Nine kinds of carbon materials were introduced into dye-sensitized solar cells (DSCs) system as counter electrodes (CEs). We also compared the electrochemical catalytic activity of these carbon materials with Pt for the reduction of triiodide to iodide by measuring cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel-polarization curve. The nine kinds of carbon materials in this work included synthesized well-ordered mesoporous carbon (Com), activated carbon (Ca), carbon black (Cb), conductive carbon (Cc), carbon dye (Cd), carbon fiber (Cf), carbon nanotube (Cn), discarded toner of a printer (Cp) and fullerene (C60). All carbon materials showed electrochemical catalytic activity for triiodide reduction in the DSCs system. In particular, the synthesized Com showed excellent electrochemical catalytic activity which can be comparable to the performance of Pt. After optimizing the proportion of TiO2 added into the carbon paste and the spray time of the carbon paste, the DSCs based on these carbon CEs achieved energy conversion efficiencies of 2.8–7.5%. The results demonstrate that carbon material is a promising substitute for the expensive Pt CE for low-cost DSCs.

A novel catalyst of WO2 nanorod for the counter electrode of dye-sensitized solar cells

Tungsten dioxide (WO(2)) nanorods were synthesized, which showed excellent catalytic activity for the reduction of triiodide to iodide. The dye-sensitized solar cell (DSC) using WO(2) as a counter electrode (CE) reached a high energy conversion efficiency of 7.25%, which can match the performance of the DSC based on a Pt CE.

Pt‐Free Counter Electrode for Dye‐Sensitized Solar Cells with High Efficiency

Dye-sensitized solar cells (DSSCs) have attracted widespread attention in recent years as potential cost-effective alternatives to silicon-based and thin-film solar cells. Within typical DSSCs, the counter electrode (CE) is vital to collect electrons from the external circuit and catalyze the I3- reduction in the electrolyte. Careful design of the CEs can improve the catalytic activity and chemical stability associated with the liquid redox electrolyte used in most cells. In this Progress Report, advances made by our groups in the development of CEs for DSSCs are reviewed, highlighting important contributions that promise low-cost, efficient, and robust DSSC systems. Specifically, we focus on the design of novel Pt-free CE catalytic materials, including design ideas, fabrication approaches, characterization techniques, first-principle density functional theory (DFT) calculations, ab-initio Car-Parrinello molecular dynamics (CPMD) simulations, and stability evaluations, that serve as practical alternatives to conventional noble metal Pt electrodes. We stress the merits and demerits of well-designed Pt-free CEs, such as carbon materials, conductive polymers, transition metal compounds (TMCs) and their corresponding hybrids. Also, the prospects and challenges of alternative Pt catalysts for their applications in new-type DSSCs and other catalytic fields are discussed.

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.

Platinum‐Free Catalysts as Counter Electrodes in Dye‐Sensitized Solar Cells

Since 1991, much progress has been made in the development of dye-sensitized solar cells (DSSCs). When compared to traditional silicon solar cells, DSSCs possess several unique advantages, such as simpler fabrication procedures, higher plasticity, higher transparency, and a greater variety of colors. Generally, a DSSC can be described by three components: a photoanode (i.e. , a dye-sensitized mesoporous semiconductor film); an electrolyte containing a redox couple; and a counter electrode (CE). Figure 1 is a schematic drawing of a DSSC. Under illumination, a sensitizer molecule (S) jumps to an excited state (S*), and the unstable S* releases a photoelectron (e ) that injects into the conduction band (CB) of the semiconductor, leaving behind a sensitizer hole (S) [actually, the excited state (S*) may relax to the ground state without release of a photoelectron, but this is not the main process] . These processes occur according to Formulae (1) and (2). Next, the photoelectrons in the CB are collected by the substrate (SB), flow through the external circuit, and reach the CE [Formulae (3) and (4)] . The oxidation state of the electrolyte (Ox) is reduced to the reduction state (Red ) by electrons at the CE, as shown in Formula (5). Meanwhile, S is regenerated by Red , which is oxidized to Ox according to Formula (6) until a circuit circle is completed. The electron transfer processes are accompanied by electron recombination. The recombination processes occur between the photoelectrons (CB) and the sensitizer holes [Formula (7)] and between the photoelectrons and Ox of the redox couple [Formula (8)] . Recombination is a major cause of efficiency loss in DSSCs and other solar cells.

Hole-Conductor-Free, Metal-Electrode-Free TiO2/CH3NH3PbI3 Heterojunction Solar Cells Based on a Low-Temperature Carbon Electrode

Low cost, high efficiency, and stability are straightforward research challenges in the development of organic-inorganic perovskite solar cells. Organolead halide is unstable at high temperatures or in some solvents. The direct preparation of a carbon layer on top becomes difficult. In this study, we successfully prepared full solution-processed low-cost TiO2/CH3NH3PbI3 heterojunction (HJ) solar cells based on a low-temperature carbon electrode. Power conversion efficiency of mesoporous (M-)TiO2/CH3NH3PbI3/C HJ solar cells based on a low-temperature-processed carbon electrode achieved 9%. The devices of M-TiO2/CH3NH3PbI3/C HJ solar cells without encapsulation exhibited advantageous stability (over 2000 h) in air in the dark. The ability to process low-cost carbon electrodes at low temperature on top of the CH3NH3PbI3 layer without destroying its structure reduces the cost and simplifies the fabrication process of perovskite HJ solar cells. This ability also provides higher flexibility to choose and optimize the device, as well as investigate the underlying active layers.

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%).