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Zhong-Sheng Wang

Bio: Zhong-Sheng Wang is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Dye-sensitized solar cell & Materials science. The author has an hindex of 17, co-authored 19 publications receiving 4740 citations.

Papers
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Journal ArticleDOI
TL;DR: The molecular design of alkyl-functionalized dyes strongly suggests the promising performance of molecular photovoltaics based on organic dyes.
Abstract: We designed and synthesized new alkyl-functionalized organic dyes, MK-1 and MK-2, for dye-sensitized solar cells (DSSCs). Based on the MK-2 dye, a high performance of efficiency (eta, 7.7%; short-circuit current density Jsc = 14.0 mA cm-2, open-circuit voltage Voc = 0.74 V, and fill factor FF = 0.74) was achieved under AM 1.5 G irradiation (100 mW cm-2). Remarkably, the relatively higher Voc for DSSCs based on MK-1 and MK-2 dyes, which have long alkyl chains, were observed among the organic dyes caused by the increasing of the electron lifetime in the conduction band of TiO2. Our molecular design of alkyl-functionalized dyes strongly suggests the promising performance of molecular photovoltaics based on organic dyes.

853 citations

Journal ArticleDOI
TL;DR: In this paper, the photovoltaic performance of dye-sensitized solar cells (DSSCs) was improved by adding n-hexyl chains to the thiophene groups.
Abstract: Novel organic dyes (MK dyes), which have a carbazole derivative as an electron donor and a cyanoacrylic acid moiety (═C(—C≡N)COOH) as an electron acceptor and an anchoring group, connected with n-hexyl-substituted oligothiophenes as a π-conjugated system, were designed and synthesized for application in dye-sensitized solar cells (DSSCs), which are one of the promising molecular photovoltaics. The photovoltaic performance of the DSSCs based on MK dyes markedly depends on the molecular structure of the dyes in terms of the number and position of n-hexyl chains and the number of thiophene moieties. Retardation of charge recombination caused by the existence of n-hexyl chains linked to the thiophene groups resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (Voc) and hence the solar-to-electric power conversion efficiency (η) of DSSCs was achieved upon addition of n-hexyl chains to the thiophene groups. In addition, the adsorption condition (amount of d...

607 citations

Journal ArticleDOI
TL;DR: In this paper, a new coumarin dye, 2-cyano-3-{5′-[1,1,6,6tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3aaza-benzo[de]anthracen-9-yl)-vinyl]-[2,2′]bithiophenyl-5-yl}acrylic acid (NKX-2883), shown in Figure
Abstract: Dye-sensitized solar cells (DSSCs) have been studied extensively as potential alternatives to conventional inorganic solid solar cells, by using wide-bandgap nanocrystalline TiO2 sensitized with ruthenium polypyridine complexes or metal-free organic dyes as photoelectrodes. Through molecular design, ruthenium complexes have achieved power-conversion efficiencies of over 11 %, while metal-free organic dyes have reached ca. 9 % power-conversion efficiency under AM 1.5 (AM: air mass) simulated solar light of 100 mW cm (1 sun). Several ruthenium polypyridyl complexes have shown their ability to withstand thermal or light-soaking stress tests for at least 1000 h while retaining an efficiency above 7 %, whereas for organic-dye-based DSSCs the longterm stability, which is the critical requirement for practical applications, so far remains a serious problem. Organic dyes are also promising for applications in DSSCs in that they have much higher molar extinction coefficients than those for ruthenium polypyridine complexes, which are favorable for light-harvesting efficiency (LHE) and hence photocurrent generation. Among the organic dye sensitizers tested in DSSCs, coumarin dyes are strong candidates because of their good photoelectric conversion properties. However, one of their drawbacks is that a high concentration of 4-tert-butylpyridine (TBP) is usually required for a high power-conversion efficiency. Under continuous light soaking of 1 sun for a short period of one day, the photovoltaic performance was observed to drop dramatically because of the dissolution of the dye into electrolyte containing 0.5 M or more TBP. Therefore, it still remains a great challenge to acquire a DSSC based on a metal-free organic dye with high efficiency that is stable in the long term. In this paper, we report a new coumarin dye, 2-cyano-3-{5′-[1-cyano-2-(1,1,6,6tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3aaza-benzo[de]anthracen-9-yl)-vinyl]-[2,2′]bithiophenyl-5-yl}acrylic acid (NKX-2883), shown in Figure 1, for use in DSSCs. These DSSCs exhibited LHE values of near unity, incident photon-to-electron conversion efficiency (IPCE) over a wide spectral region on transparent TiO2 films of only 6 lm thickness, and maintained ca. 6 % power-conversion efficiency under continuous light soaking of 1 sun at 50–55 °C for 1000 h. Figure 2a shows the UV-vis absorption spectrum for NKX2883 in an ethanol solution. NKX-2883 exhibited two p–p* electron-transition peaks (426 and 552 nm) in the visible region. Compared to NKX-2677 (2-cyano-3-[5’-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-azabenzo[de]anthracen-9-yl)-[2,2’]bithiophenyl-5-yl]acrylic acid), one of the best organic dyes for DSSCs reported previously, the introduction of one more CN group into the molecular frame decreases the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), thus extending the maximum absorption from 511 to 552 nm. This red-shift may favor light harvesting and hence photocurrent generation in DSSCs, as will be discussed below. The 552 nm peak showed a broad feature with a full width at half-maximum absorbance of ca. 110 nm, comparable to that for ruthenium polypyridyl complexes, contributing broadly to the high LHE. The molar extinction coefficient (e) of NKX-2883 in ethanol was determined to be 9.74 × 10 dm mol cm at 552 nm, which is about seven times larger than that of N3 (cis-di(thiocyanate)-bis(2,2’-bipyridyl-4,4’-dicarboxylic acid); e= 1.42 × 10 dm mol cm at 532 nm), and 60 % larger than that for NKX-2677 (e= 6.43 × 10 dm mol cm at 511 nm). The LUMO (–0.69 V vs the normal hydrogen electrode (NHE)) of NKX-2883 is more negative than the conduction-band edge of TiO2 (–0.5 V vs NHE), [23] ensuring that electron injection from the excited dye to the conduction band of TiO2 is thermodynamically favorable. The dye-loaded films were obtained by dipping the TiO2 film in dye solutions with different concentrations: 0.02, 0.1, 0.3, and 1.0 mM. The normalized UV-vis absorption spectra for dye-loaded films are plotted in Figure 2b. It is evident that the spectrum becomes slightly broader with an increasing conC O M M U N IC A TI O N

578 citations

Journal ArticleDOI
TL;DR: Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.
Abstract: We have developed oligothiophene-containing coumarin dyes fully functionalized for dye-sensitized nanocrystalline TiO(2) solar cells (DSSCs). DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-800 nm. A solar energy-to-electricity conversion efficiency (eta) of 7.4% was obtained with a DSSC based on 2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid (NKX-2677) under simulated AM 1.5G irradiation (100 mW cm(-2)) with a mask: short-circuit current density (J(sc)) = 13.5 mA cm(-2); open-circuit voltage (V(oc)) = 0.71 V; fill factor (FF) = 0.77. Transient absorption spectroscopy measurements indicated that electron injection from NKX-2677 to the conduction band of TiO(2) is very rapid (<100 fs), which is much faster than the emission lifetime of the dye (1.0 ns), giving a highly efficient electron injection yield of near unity.

555 citations

Journal ArticleDOI
TL;DR: In this article, a new coumarin dye, 2-cyano-3-(5-{2-[5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6)-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye
Abstract: This paper reports a new coumarin dye, 2-cyano-3-(5-{2-[5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl)-thiophen-2-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye-sensitized solar cells (DSSCs). Under illumination of simulated AM1.5G solar light (100 mW cm-2) with an aperture black mask, 5.0% of power conversion efficiency [short-circuit photocurrent density (Jsc) = 12.0 mA cm-2, open-circuit photovoltage (Voc) = 0.59 V, and fill factor (FF) = 0.71] was obtained for NKX-2700 based DSSC, which was significantly improved to 8.2% (Jsc = 15.9 mA cm-2, Voc = 0.69 V, FF = 0.75) upon addition of 120 mM deoxycholic acid (DCA) to the dye solution for TiO2 sensitization. Coadsorption of DCA decreased dye coverage by ∼50% but significantly improved the Jsc by 33%. The breakup of π-stacked aggregates might improve electron injection yield and thus Jsc. Electrochemical impedance data indicate that the electron lifetime was improved by coa...

497 citations


Cited by
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Journal ArticleDOI
TL;DR: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency as mentioned in this paper, and many DSC research groups have been established around the world.
Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

8,707 citations

Journal ArticleDOI
TL;DR: Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting and its Applications d0 Metal Oxide Photocatalysts 6518 4.4.1.
Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

6,332 citations

Journal ArticleDOI
04 Nov 2011-Science
TL;DR: In this article, a Co(II/III)tris(bipyridyl)-based redox electrolyte was used in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8).
Abstract: The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.

5,462 citations

Journal Article
01 Jan 2011-Science
TL;DR: Mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer are reported, enabling attainment of strikingly high photovoltages approaching 1 volt.
Abstract: Simultaneous modification of the dye and redox shuttle boosts the efficiency of a dye-sensitized solar cell. The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.

5,385 citations