Boosting the Photovoltage of Dye-Sensitized Solar Cells with Thiolated Gold Nanoclusters.

Glutathione-capped gold nanoclusters (Aux-GSH NCs) are anchored along with a sensitizing squaraine dye on a TiO2 surface to evaluate the cosensitizing role of Au(x)-GSH NCs in dye-sensitized solar cells (DSSCs). Photoelectrochemical measurements show an increase in the photoconversion efficiency of DSSCs when both sensitizers are present. The observed photoelectrochemical improvements in cosensitized DSSCs are more than additive effects as evident from the increase in photovoltage (ΔV as high as 0.24 V) when Au(x)-GSH NCs are present. Electron equilibration and accumulation within gold nanoclusters increase the quasi-Fermi level of TiO2 closer to the conduction band and thus decrease the photovoltage penalty. A similar beneficial role of gold nanoclusters toward boosting the V(oc) and enhancing the efficiency of Ru(II) polypyridyl complex-sensitized solar cells is also discussed.

CdSeS Nanowires: Compositionally Controlled Band Gap and Exciton Dynamics.

CdS, CdSe, and ternary CdSexS(1-x) are some of the most widely studied II-VI semiconductors due to their broad range of applications and promising performance in numerous systems. One-dimensional semiconductor nanowires offer the ability to conduct charges efficiently along the length of the wire, which has potential charge transport benefits compared to nanoparticles. Herein, we report a simple, inexpensive synthetic procedure for high quality CdSeS nanowires where the composition can be easily modulated from pure CdSe to pure CdS by simply adjusting the Se:S precursor ratio. This allows for tuning of the absorption and emission properties of the nanowires across the visible spectrum. The CdSeS nanowires have a wurtzite crystal structure and grow along the [001] direction. As measured by femtosecond transient absorption spectroscopy, the short component of the excited state lifetime remains relatively constant at ∼10 ps with increasing Se; however, the contribution of this short lifetime component increased dramatically from 8.4% to 57.7% with increasing Se content. These CdSeS nanowires offer facile synthesis and widely adjustable optical properties, characteristics that give them broad potential applications in the fields of optoelectronics, and photovoltaics.

Metal-cluster-sensitized solar cells. A new class of thiolated gold sensitizers delivering efficiency greater than 2%.

A new class of metal-cluster sensitizers has been explored for designing high-efficiency solar cells. Thiol-protected gold clusters which exhibit molecular-like properties have been found to inject electrons into TiO2 nanostructures under visible excitation. Mesoscopic TiO2 films modified with gold clusters deliver stable photocurrent of 3.96 mA/cm(2) with power conversion efficiencies of 2.3% under AM 1.5 illumination. The overall absorption features and cell performance of metal-cluster-sensitized solar cells (MCSCs) are comparable to those of CdS quantum-dot-based solar cells (QDSCs). The relatively high open-circuit voltage of 832 mV and fill factor of 0.7 for MCSCs as compared to QDSCs show the viability of these new sensitizers as alternatives to semiconductor QDs and sensitizing dyes in the next generation of solar cells. The superior performance of MCSCs discussed in this maiden study lays the foundation to explore other metal clusters with broader visible absorption.

Metagenome Analysis of Protein Domain Collocation within Cellulase Genes of Goat Rumen Microbes.

In this study, protein domains with cellulase activity in goat rumen microbes were investigated using metagenomic and bioinformatic analyses. After the complete genome of goat rumen microbes was obtained using a shotgun sequencing method, 217,892,109 pair reads were filtered, including only those with 70% identity, 100-bp matches, and thresholds below E(-10) using METAIDBA. These filtered contigs were assembled and annotated using blastN against the NCBI nucleotide database. As a result, a microbial community structure with 1431 species was analyzed, among which Prevotella ruminicola 23 bacteria and Butyrivibrio proteoclasticus B316 were the dominant groups. In parallel, 201 sequences related with cellulase activities (EC.3.2.1.4) were obtained through blast searches using the enzyme.dat file provided by the NCBI database. After translating the nucleotide sequence into a protein sequence using Interproscan, 28 protein domains with cellulase activity were identified using the HMMER package with threshold E values below 10(-5). Cellulase activity protein domain profiling showed that the major protein domains such as lipase GDSL, cellulase, and Glyco hydro 10 were present in bacterial species with strong cellulase activities. Furthermore, correlation plots clearly displayed the strong positive correlation between some protein domain groups, which was indicative of microbial adaption in the goat rumen based on feeding habits. This is the first metagenomic analysis of cellulase activity protein domains using bioinformatics from the goat rumen.

Synchronized energy and electron transfer processes in covalently linked CdSe-squaraine dye-TiO2 light harvesting assembly.

Manipulation of energy and electron transfer processes in a light harvesting assembly is an important criterion to mimic natural photosynthesis. We have now succeeded in sequentially assembling CdSe quantum dot (QD) and squaraine dye (SQSH) on TiO(2) film and couple energy and electron transfer processes to generate photocurrent in a hybrid solar cell. When attached separately, both CdSe QDs and SQSH inject electrons into TiO(2) under visible-near-IR irradiation. However, CdSe QD if linked to TiO(2) with SQSH linker participates in an energy transfer process. The hybrid solar cells prepared with squaraine dye as a linker between CdSe QD and TiO(2) exhibited power conversion efficiency of 3.65% and good stability during illumination with global AM 1.5 solar condition. Transient absorption spectroscopy measurements provided further insight into the energy transfer between excited CdSe QD and SQSH (rate constant of 6.7 × 10(10) s(-1)) and interfacial electron transfer between excited SQSH and TiO(2) (rate constant of 1.2 × 10(11) s(-1)). The synergy of covalently linked semiconductor quantum dots and near-IR absorbing squaraine dye provides new opportunities to harvest photons from selective regions of the solar spectrum in an efficient manner.

Know thy nano neighbor. Plasmonic versus electron charging effects of metal nanoparticles in dye-sensitized solar cells.

Neighboring metal nanoparticles influence photovoltaic and photocatalytic behavior of semiconductor nanostructures either through Fermi level equilibration by accepting electrons or inducing localized surface plasmon effects. By employing SiO(2)- and TiO(2)-capped Au nanoparticles we have identified the mechanism with which the performance of dye-sensitized solar cells (DSSC) is influenced by the neighboring metal nanoparticles. The efficiency of an N719 dye-sensitized solar cell (9.3%) increased to 10.2% upon incorporation of 0.7% Au@SiO(2) and to 9.8% upon loading of 0.7% Au@TiO(2) nanoparticles. The plasmonic effect as monitored by introducing Au@SiO(2) in DSSC produces higher photocurrent. However, Au nanoparticles undergo charge equilibration with TiO(2) nanoparticles and shift the apparent Fermi level of the composite to more negative potentials. As a result, Au@TiO(2) nanoparticle-embedded DSSC exhibit higher photovoltage. A better understanding of these two effects is crucial in exploiting the beneficial aspects of metal nanoparticles in photovoltaics.

A new class of cyclometalated ruthenium sensitizers of the type CNN for efficient dye-sensitized solar cells.

A new class of cyclometalated ruthenium sensitizers incorporating a CNN ligand and conjugated 2,2'-bipyridine in the ancillary ligand have been designed and synthesized. The photovoltaic performance of JK-206 using an electrolyte containing 0.6 M 1,2-dimethyl-3-propylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, and 0.5 M tert-butylpyridine in CH(3)CN gave a short-circuit photocurrent density of 19.63 mA cm(-2), an open-circuit voltage of 0.74 V, and a fill factor of 0.72, affording an overall conversion efficiency of 10.39%. The efficiency is the highest one reported for dye-sensitized solar cells based on the cyclometalated ruthenium sensitizer of the type CNN. Moreover, the same device using a polymer gel electrolyte exhibited a remarkable stability under 1000 h of light soaking at 60 °C, retaining 91% of the initial efficiency of 7.14%.

Supersensitization of CdS quantum dots with a near-infrared organic dye: toward the design of panchromatic hybrid-sensitized solar cells.

The photoresponse of quantum dot solar cells (QDSCs) has been successfully extended to the near-IR (NIR) region by sensitizing nanostructured TiO(2)-CdS films with a squaraine dye (JK-216). CdS nanoparticles anchored on mesoscopic TiO(2) films obtained by successive ionic layer adsorption and reaction (SILAR) exhibit limited absorption below 500 nm with a net power conversion efficiency of ~1% when employed as a photoanode in QDSC. By depositing a thin barrier layer of Al(2)O(3), the TiO(2)-CdS films were further modified with a NIR absorbing squaraine dye. Quantum dot sensitized solar cells supersensitized with a squariand dye (JK-216) showed good stability during illumination with standard global AM 1.5 solar conditions, delivering a maximum overall power conversion efficiency (η) of 3.14%. Transient absorption and pulse radiolysis measurements provide further insight into the excited state interactions of squaraine dye with SiO(2), TiO(2), and TiO(2)/CdS/Al(2)O(3) films and interfacial electron transfer processes. The synergy of combining semiconductor quantum dots and NIR absorbing dye provides new opportunities to harvest photons from different regions of the solar spectrum.

Synthesis of annulated thiophene perylene bisimide analogues: their applications to bulk heterojunction organic solar cells.

Annulated thiophene perylene bisimides and their triphenyl-amine based oligomers have been synthesized. One of the oligomers FPTTPA has been demonstrated to be an efficient electron donor in bulk heterojunction (BHJ) organic solar cells, giving a power conversion efficiency of 1.42%.

Efficient and stable panchromatic squaraine dyes for dye-sensitized solar cells.

A new series of stable, unsymmetrical squaraine near-IR sensitizers (JK-216 and JK-217), which are assembled using both thiophenyl pyrrolyl and indolium groups, exhibit a panchromatic light harvesting up to 780 nm. The JK-216 based cell exhibited a record efficiency of 6.29% for near-IR DSSCs. In addition, the JK-217 device showed an excellent stability under a light soaking test at 60 °C for 1000 h.

New efficient ruthenium sensitizers with unsymmetrical indeno[1,2-b]thiophene or a fused dithiophene ligand for dye-sensitized solar cells.

Two novel ruthenium sensitizers containing unsymmetrical indeno[1,2-b]thiophene or a fused dithiophene unit in the ancillary ligand have been designed and synthesized. The photovoltaic performance of JK-188 using an electrolyte consisting of 0.6 M 1,2-dimethyl-3-propylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, 0.05 M guanidinium thiocyanate, and 0.5 M tert-butylpyridine in acetonitrile revealed a short-circuit photocurrent density of 18.60 mA/cm(2), an open-circuit voltage of 0.72 V, and a fill factor of 0.71, yielding an overall conversion efficiency of 9.54%. The cell exhibits a remarkable stability under 1000 h of light soaking at 60 °C using a quasi-solid-state electrolyte consisting of 5 wt % poly(vinylidenefluoride-co-hexafluoropropylene), 0.6 M 1-propyl-2,3-dimethylimidazolium iodide, 0.5 M N-methylbenzimidazole, and 0.1 M I(2) in 3-methoxypropionitrile, retaining 97% of the initial efficiency (7.38%).

High molar extinction coefficient organic sensitizers for efficient dye-sensitized solar cells.

We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene-vinylene-thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK-113-sensitized cell gave a short circuit photocurrent density (J(sc)) of 17.61 mA cm(-2), an open-circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 72%, corresponding to an overall conversion efficiency (eta) of 9.1%. The incident monochromatic photo-to-current conversion efficiency (IPCE) of JK-113 exceeds 80% over the spectral region from 400 to 640 nm, reaching its maximum of 93% at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar-cell devices based on the sensitizer JK-113 in conjunction with a volatile electrolyte and a solvent-free ionic liquid electrolyte gave high conversion efficiencies of 9.1% and 7.9%, respectively. The JK-113-based solar cell fabricated using a solvent-free ionic liquid electrolyte showed excellent stability under light soaking at 60 degrees C for 1000 h.

Enhanced photovoltaic performance and long-term stability of quasi-solid-state dye-sensitized solar cells via molecular engineering.

Organic dyes with long alkyl chains have been synthesized and demonstrated to be highly efficient sensitizers for liquid and quasi-solid-state solar cells, giving power conversion efficiencies of 8.31-8.39% and 7.03-7.31% under AM 1.5 G irradiation, respectively.

Molecular engineering of organic sensitizers containing p-phenylene vinylene unit for dye-sensitized solar cells.

Three organic sensitizers containing bis-dimethylfluorenyl amino donor and a cyanoacrylic acid acceptor bridged by p-phenylene vinylene unit were synthesized. The power conversion efficiency was quite sensitive to the length of bridged phenylene vinylene groups. A nanocrystalline TiO2 dye-sensitized solar cell was fabricated using three sensitizers. The maximum power conversion efficiency of JK-59 reached 7.02%.

Photoregulated fluorescence switching in axially coordinated tin(IV) porphyrinic dithienylethene.

Photochromic fluorophore Sn(TTP)(DTE)2 , in which two phenolic derivatives of 1,2-dithienylethene are axially coordinated to (5,10,15,20-tetratolylporphyrinato)tin(IV) in trans position, has been synthesized and fully characterized by various spectroscopic methods. We have also investigated the photoregulated fluorescence switching behavior of Sn(TTP)(DTE)2 . The fluorescence of the porphyrin macrocycle in Sn(TTP)(DTE) 2 greatly depends on the state of the 1,2-dithienyletene photochromic switch. In the open state (Sn(TTP)(o-DTE)2), the porphyrin exhibits high fluorescence intensity at 609 and 664 nm when excited at 410 nm. When the photocyclization reaction was carried out by irradiating Sn(TTP)(o-DTE)2 with the UV light (approximately 365 nm), the fluorescence intensity of the porphyrin macrocycle decreased. Back irradiation with visible light at wavelengths greater than 500 nm regenerated Sn(TTP)(o-DTE)2 and almost restored the original fluorescence spectrum. The fluorescence intensity of the porphyrin fluorophore is efficiently regulated by photochromic switching between Sn(TTP)(o-DTE)2 and Sn(TTP)(c-DTE)2 in several cycles, clearly demonstrating that the Sn(TTP)(DTE)2 can act as a system for reversible data processing using fluorescence as the detection method.

Phenomenally high molar extinction coefficient sensitizer with "donor-acceptor" ligands for dye-sensitized solar cell applications.

A phenomenally high molar extinction coefficient heteroleptic ruthenium(II) complex [Ru(4,4'-carboxylic acid-2,2'-bipyridine)(4,4'-(4-{4-methyl-2,5-bis[3-methylbutoxy]styryl}-2,5-bis[3-methylbutoxy]-2,2'-bipyridine)(NCS) 2] ( DCSC13) was synthesized by incorporating donor-acceptor ligands. The absorption spectrum of the DCSC13 sensitizer is dominated by metal-to-ligand charge-transfer transitions (MLCT) in the visible region, with absorption maxima appearing at 442 and 554 nm. The lowest MLCT absorption bands are red-shifted, and the molar extinction coefficients of these bands are significantly higher at 72,100 and 30,600 M(-1) cm(-1), respectively, when compared to those of the analogous [Ru(4,4'-carboxylic acid-2,2'-bipyridine)(4,4'-dimethyl-2,2'-bipyridine)(NCS)2] (N820) sensitizer. The DCSC13 complex, when anchored on nanocrystalline TiO 2 films, exhibited increased short-circuit photocurrent and consequent power-conversion efficiency when compared with the N820 sensitizer.

Photochromism and electrical transport characteristics of a dyad and a polymer with diarylethene and quinoline units.

The synthesis of a series of photochromic compounds incorporating a phenylquinoline unit and the photophysical and electric transport properties are described. The dyad and polymer with a quinoline unit show a high quantum yield due to the enforced antiparallel conformation of the dithienylethene moieties. High carrier conductivity was observed in the closed form of the diarylethene with a phenylquinoline unit.