Yan Cui

Bio: Yan Cui is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Carbazole & Dye-sensitized solar cell. The author has an hindex of 14, co-authored 14 publications receiving 2636 citations.

Hexylthiophene-Functionalized Carbazole Dyes for Efficient Molecular Photovoltaics: Tuning of Solar-Cell Performance by Structural Modification

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...

A High‐Light‐Harvesting‐Efficiency Coumarin Dye for Stable Dye‐Sensitized Solar Cells

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

Thiophene-Functionalized Coumarin Dye for Efficient Dye-Sensitized Solar Cells: Electron Lifetime Improved by Coadsorption of Deoxycholic Acid

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...

Molecular Design of Coumarin Dyes for Stable and Efficient Organic Dye-Sensitized Solar Cells

Abstract: A series of coumarin dyes (NKX-2593, NKX-2807, and NKX-2883) with one or two -CN groups as electron acceptors were synthesized and applied as dye sensitizers for dye-sensitized solar cells. Compared with the dye containing one -CN group, linking one more -CN group to the π-conjugation bridge positively shifts the lowest unoccupied molecular orbital and thus red-shifts the maximum absorption band, harvesting more photons in the long-wavelength region for photoelectric conversion. Among the three dyes studied, NKX-2883 showed the best photovoltaic performance, yielding 7.6% power conversion efficiency using a volatile electrolyte and demonstrating good photostability under visible light soaking with 6% of power conversion efficiency for 1000 h using a nonvolatile electrolyte.

Substituted carbazole dyes for efficient molecular photovoltaics: long electron lifetime and high open circuit voltage performance

Abstract: We designed and synthesized new substituted carbazole dyes, MK-14 and -16, for dye-sensitized solar cells (DSSCs) employing the I−/I3−redox couple. By the addition of a hexyloxyphenyl substituent to previously reported carbazole dyes MK-1 and -2, the electron lifetime and open circuit voltage of the DSSCs employing these dyes were increased, showing comparable values with those using a conventional Ru complex dye. This result was achieved by the retardation of the charge recombination, caused by more effective blocking of the I3− ion in the electrolyte than that in the cases of MK-1 and -2. The result shows the importance of the position of alkyl chains attached to the main framework of dye molecules.

Dye-Sensitized Solar Cells

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 ...

Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules

Abstract: Dye-sensitized solar cells (DSSC) have attracted considerable attention in recent years as they offer the possibility of low-cost conversion of photovoltaic energy This Review focuses on recent advances in molecular design and technological aspects of metal-free organic dyes for applications in dye-sensitized solar cells Special attention has been paid to the design principles of these dyes and on the effect of various electrolyte systems Cosensitization, an emerging technique to extend the absorption range, is also discussed as a way to improve the performance of the device In addition, we report on inverted dyes for photocathodes, which constitutes a relatively new approach for the production of tandem cells Special consideration has been paid to the correlation between the molecular structure and physical properties to their performance in DSSCs

Enhancing solar cell efficiency: the search for luminescent materials as spectral converters

Abstract: Photovoltaic (PV) technologies for solar energy conversion represent promising routes to green and renewable energy generation. Despite relevant PV technologies being available for more than half a century, the production of solar energy remains costly, largely owing to low power conversion efficiencies of solar cells. The main difficulty in improving the efficiency of PV energy conversion lies in the spectral mismatch between the energy distribution of photons in the incident solar spectrum and the bandgap of a semiconductor material. In recent years, luminescent materials, which are capable of converting a broad spectrum of light into photons of a particular wavelength, have been synthesized and used to minimize the losses in the solar-cell-based energy conversion process. In this review, we will survey recent progress in the development of spectral converters, with a particular emphasis on lanthanide-based upconversion, quantum-cutting and down-shifting materials, for PV applications. In addition, we will also present technical challenges that arise in developing cost-effective high-performance solar cells based on these luminescent materials.

Functional oligothiophenes: molecular design for multidimensional nanoarchitectures and their applications.

Abstract: 3.2. Thienothiophenes 1216 3.2.1. Thieno[3,4-b]thiophene Analogues 1216 3.2.2. Thieno[3,2-b]thiophene Analogues 1217 3.2.3. Thieno[2,3-b]thiophene Analogues 1218 3.3. , ′-Bridged Bithiophenes 1219 3.3.1. Dithienothiophene (DTT) Analogues 1220 3.3.2. Dithieno[3,2-b:2′3′-d]thiophene-4,4-dioxides 1221 3.3.3. Dithienosilole (DTS) Analogues 1221 3.3.4. Cyclopentadithiophene (CPDT) Analogues 1221 3.3.5. Nitrogen and Phosphor Atom Bridged Bithiophenes 1222

Porphyrin-sensitized solar cells

Abstract: Nature has chosen chlorophylls in plants as antennae to harvest light for the conversion of solar energy in complicated photosynthetic processes. Inspired by natural photosynthesis, scientists utilized artificial chlorophylls – the porphyrins – as efficient centres to harvest light for solar cells sensitized with a porphyrin (PSSC). After the first example appeared in 1993 of a porphyrin of type copper chlorophyll as a photosensitizer for PSSC that achieved a power conversion efficiency of 2.6%, no significant advance of PSSC was reported until 2005; beta-linked zinc porphyrins were then reported to show promising device performances with a benchmark efficiency of 7.1% reported in 2007. Meso-linked zinc porphyrin sensitizers in the first series with a push–pull framework appeared in 2009; the best cell performed comparably to that of a N3-based device, and a benchmark 11% was reported for a porphyrin sensitizer of this type in 2010. With a structural design involving long alkoxyl chains to envelop the porphyrin core to suppress the dye aggregation for a push–pull zinc porphyrin, the PSSC achieved a record 12.3% in 2011 with co-sensitization of an organic dye and a cobalt-based electrolyte. The best PSSC system exhibited a panchromatic feature for light harvesting covering the visible spectral region to 700 nm, giving opportunities to many other porphyrins, such as fused and dimeric porphyrins, with near-infrared absorption spectral features, together with the approach of molecular co-sensitization, to enhance the device performance of PSSC. According to this historical trend for the development of prospective porphyrin sensitizers used in PSSC, we review systematically the progress of porphyrins of varied kinds, and their derivatives, applied in PSSC with a focus on reports during 2007–2012 from the point of view of molecular design correlated with photovoltaic performance.