Stable, high-efficiency ionic-liquid-based mesoscopic dye-sensitized solar cells

Efficient and stable mesoscopic dye-sensitized solar cells (DSCs) introducing a low-viscosity binary ionic liquid (1-propyl-3-methyl-imidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium tetracyanoborate (EMIB(CN)(4))) electrolyte in combination with a new high-molar-extinction-coefficient ruthenium complex, Ru(2,2'-bipyridine-4,4'-dicarboxylic acid)(4,4'-bis(2-(4-tert-butyloxy -phenyl)ethenyl) -2,2'-bipyridine) (NCS)(2), are demonstrated. The dependence of photovoltaic performance, charge transport and electron lifetime on the composition of the binary ionic-liquid electrolyte with different ratios of PMII/EMIB(CN)(4) were investigated by electrochemical impedance and photovoltage transient techniques. A photovoltaic conversion efficiency of 7.6 % was obtained under simulated full sunlight illumination, which is a record for solvent-free DSCs. These devices exhibit excellent stability at 80 degrees C in the dark or under visible-light soaking at 60 degrees C during 1000 h of accelerated tests.     

Efficient and Stable Solid‐State Dye‐Sensitized Solar Cells Based on a High‐Molar‐Extinction‐Coefficient Sensitizer

The high‐molar‐extinction‐coefficient heteroleptic ruthenium dye, cis‐Ru (4,4′‐bis(5‐octylthieno[3,2‐b] thiophen‐2‐yl)‐2,2′‐bipyridine) (4,4′‐dicarboxyl‐2,2′‐bipyridine) (NCS)₂, exhibits an AM 1.5 solar (100 mW cm^?2)‐to‐electric power‐conversion efficiency of 4.6% in a solid‐state dye‐sensitized solar cell (SSDSC) with 2,2′, 7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)9,9′‐spirobifluorene (spiro‐MeOTAD) as the organic hole‐transporting material. These SSDSC devices exhibit good durability during accelerated tests under visible‐light soaking for 1000 h at 60 °C. This demonstration elucidates a class of photovoltaic devices with potential for stable and low‐cost power generation. The electron recombination dynamics and charge collection that take place at the dye‐sensitized heterojunction are studied by means of impedance and transient photovoltage decay techniques.     

Influence of donor moiety in ruthenium sensitizers on the properties of dye-sensitized solar cells

Heteroleptic ruthenium complexes cis-[Ru(H2dcbpy)(L)(NCS)2], where H2dcbpy is 4,4'-dicarboxylic acid-2,2'-bipyridine and L is 4-(4-(N,N-di-(p-hexyloxyphenyl)-amino)styryl)-4'-methyl-2,2'-bipyridine (Rut-A) or 4-(4'-(3,6-dihexyloxycarbazole-9-yl)-styryl)-4'-methyl-2,2'-bipyridine (Rut-B), have been synthesized and characterized by NMR, UV-Vis spectroscopy, and cyclic voltammogram. The effect of different electron donors on the properties of dye-sensitized solar cells has been studied. The power conversion efficiency of DSSC based on Rut-B is 6.1% while Rut-A delivered a lower efficiency of 4.52% under the same device fabrication and measuring conditions. The better photovoltaic performance of Rut-B is mainly associated with enhanced dye absorptivity and charge recombination suppression.     

Controlled dissolution of polystyrene nanobeads: transition from liquid electrolyte to gel electrolyte

The widespread commercialization of dye-sensitized solar cells (DSSCs) remains limited because of the use of highly volatile liquid electrolytes. Recently, gel-type quasi-solid electrolytes containing a polymer additive or inorganic nanomaterial have shown promising results in terms of the cell efficiency. However, most gel electrolytes have serious obstacles for pore-filling because of their high viscosity. Herein, we report the first observation of the transition from a liquid to a gel electrolyte after filling the cell with the liquid electrolyte using the controlled dissolution of polystyrene nanobeads on the counter electrode, suggesting that the pore-filling problem can be diminished in quasi-solid state DSSCs. The time-resolved solidification allows for the preparation of the gel electrolyte without interfering with the cell performance. The optimal DSSC composed of the gel electrolyte exhibits almost the same power conversion efficiency as the liquid electrolyte based DSSC when measured using an AM1.5G solar simulator at 100 mW/cm(2) light illumination. Moreover, the long-term stability of the DSSC was greatly improved.     

Enhanced light harvesting from Först-type resonance energy transfer in the quasi-solid state dye-sensitized solar cells

The demonstrated F?rst-type resonance energy transfer (FRET) is demonstrated in quasi-solid type dye-sensitized solar cells between organic fluorescence materials as an energy donor doped in polymeric gel electrolyte and a ruthenium complex as an energy acceptor on the surface of TiO2. Strong spectral overlap of emission/absorption of the energy donor and acceptor is required to obtain high FRET efficiency. The judicious choice of the energy donor allows the enhancement of the light harvesting characters of the energy acceptor (N3) in quasi-solid dye sensitized solar cells which increases the power conversion efficiency by 25% compare to that of a pristine cell. The optimized cell architecture fabricated with the quasi-solid type electrolyte containing fluorescence materials shows a maximum efficiency of 5.08% with a short-circuit current density (J(sc)) of 12.63 mA/cm2, and an open-circuit voltage (V(oc)) of 0.70 V under illumination of simulated solar light (AM 1.5, 100 mW/cm2).     

High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts

Low-cost excitonic solar cells based on organic optoelectronic materials are receiving an ever-increasing amount of attention as potential alternatives to traditional inorganic photovoltaic devices. In this rapidly developing field, the dye-sensitized solar cell (DSC) has achieved so far the highest validated efficiency of 11.1% (ref. 2) and remarkable stability. However, the cells with the best performance use volatile solvents in their electrolytes, which may be prohibitive for outdoor solar panels in view of the need for robust encapsulation. Solvent-free room-temperature ionic liquids have been pursued as an attractive solution to this dilemma, and device efficiencies of over 7% were achieved by using some low-viscosity formulations containing 1-ethyl-3-methylimidazolium thiocyanate, selenocyanate, tricyanomethide or tetracyanoborate. Unfortunately, apart from tetracyanoborate, all of these low-viscosity melts proved to be unstable under prolonged thermal stress and light soaking. Here, we introduce the concept of using eutectic melts to produce solvent-free liquid redox electrolytes. Using a ternary melt in conjunction with a nanocrystalline titania film and the amphiphilic heteroleptic ruthenium complex Z907Na (ref. 10) as a sensitizer, we reach excellent stability and an unprecedented efficiency of 8.2% under air-mass 1.5 global illumination. Our results are of importance to realize large-scale outdoor applications of mesoscopic DSCs.     

Synthesis of fluorene-based semiconducting copolymers for organic solar cells

Semiconducting polymers composed of 2,2'-(9,9-dioctyl-9H-fluorene-2,7-diyl)dithiophenes (F8T2s) and (2E,2'E)-3,3'-(2,5-bis(octyloxy)-1,4-phenylene) bis(2-(5-bromothiophene-2-yl)acrylonitrile)s (OPTANs) have been synthesized through Pd(O)-catalyzed Suzuki coupling polymerization by controlling the monomer ratio. The synthesized polymers were confirmed to exhibit good solubility in common solvents, simple processability, and thermal stability up to 350 degrees C. The highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs), and optical band-gap energies were determined using cyclic voltammetry (CV) and UV-visible spectrometry. The synthesized polymers showed their maximum absorption and edge at around 520 and 650 nm, respectively. The optical band-gap energies of the polymers were determined to be 1.89 eV. Bulk heterojunction organic solar cells were fabricated using the conjugated polymer as the electron donor, and 6,6-phenyl C61-butyric acid methylester (PC61BM) or 6,6-phenyl C71-butyric acid methylester (PC71BM) as the electron acceptor. The power conversion efficiencies (PCEs) of the solar cells based on polymer:PC71BM (1:1) and polymer:PC71BM (1:2) were 0.68% and 1.22%, respectively, under air mass 1.5 global (AM 1.5 G) illumination at 100 mW/cm2.     

Photoelectrochemical polymerization of thiophene on self-assembled RuL2(NCS)2/di(3-aminopropyl)viologen on indium thin oxide

Polythiophene layers were formed on self-assembled monolayers (SAMs)/indium tin oxide (ITO) using photoelectrochemical polymerization. The SAMs on ITO was prepared using Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 and di(3-aminopropyl)viologen. The photoelectrochemically polymerized polythiophene layers on SAMs/ITO were characterized using UV-vis. absorption spectroscopy, atomic force microscopy, scanning electron microscopy, and cyclic voltammetry. The polymer layers have thickness of 360 nm, a dense surface morphology, optical gap of 2.38 eV, highest occupied molecular orbital of -5.2 eV and lowest unoccupied molecular orbital of -2.82 eV. In photoelectrochemical cells, the polythiophene on SAMs/ITO electrode showed a photocurrent of 5 microA/cm2.     

Synthesis and characterization of new dithienosilole-based copolymers for polymer solar cells

A series of dithienosilole-based copolymers, poly [(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-5,5'-diyl] (P1), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,2'-bithiazole)-5,5'-diyl] (P2), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2, 6-diyl-alt-(10 -methyl-phenothiazine)-3,7-diyl](P3), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-9,10-anthracene)-5,5'-diyl] (P4) were synthesized by the Pd-catalyzed Stille polymerization method. Electron-deficient benzothiadiazole and bithiazole units and electron-rich phenothiazine and anthracene moieties were incorporated into the polymer backbone to obtain the broad absorption spectrum and to improve the hole-transporting characteristics, respectively. The polymer solar cell (PSC) was fabricated with a layered structure of ITO/PEDOT:PSS/polymer:C71-PCBM (1:3)/LiF/Al. The best performance of PSC was obtained at P3:C71-PCBM which reaches a power conversion efficiency (PCE) of 1.18%, with a short circuit current density (J(sc)) of 4.75 mA/cm2, an open circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 0.35 under AM 1.5G irradiation (100 mW/cm2).     

Photovoltaic performance of ruthenium complex dye associated with number and position of carboxyl groups on bipyridine ligands

A series of ruthenium complex dyes with different number and position of carboxyl groups on bipyridine ligands, such as Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)(4,4′-dimethyl-2,2′- bipyridine)(NCS)₂ (denoted as Ru1A), Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)₂(NCS)₂ (Ru11A), Ru(4,4′-dicarboxyl-2,2′-bipyridine)(4,4′-dimethyl-2,2′-bipyridine)(NCS)₂ (Ru2A), and Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)(4,4′-dicarboxyl-2,2′-bipyridine)(NCS)₂ (Ru3A) were synthesized and compared with Ru(4,4′-dicarboxyl-2,2′-bipyridine)₂ (NCS)₂, commonly known as N3 dye for the adsorption behavior on the TiO₂ surface and photovoltaic properties of dye-sensitized solar cells. The experimental results show that the tilt angle of ruthenium dyes on the TiO₂ surface which is dependent on the number and position of their carboxyl groups strongly affected the photovoltaic performance.     

Pressing effect in polymer solar cells with bulk heterojunction nanolayers

We report the effect of pressing light-absorbing layers on the performance of polymer solar cells. The light-absorbing active layer was prepared on the transparent conducting oxide coated substrates from solutions that contain a mixture of regioregular poly(3-hexylthiophene) and soluble fullerene molecules. The active layers were pressed using a home-built micro-press system by controlling temperature and pressure, followed by the top electrode deposition. The surface of the active layers pressed was examined using atomic force microscope, while the photovoltaic characteristics of devices were measured under simulated solar light illumination (air mass 1.5 G, 100 mW/cm2). Results showed that the dark current of devices was noticeably increased by pressing the active layer without respect to the pressing temperature. The highest power conversion efficiency was achieved for the device with the active layer pressed under 10 kgf at 70 degrees C. The result was explained in terms of surface morphology and thermophysical effect.     

Photosensitization of Nanocrystalline SnO2 Films with a tris(2,2'-Bipyridine) Ruthenium(II)-Fullerene Dyad

A photoelectrochemical study of a tris(2,2'-bipyridine)ruthenium(II)-C₆₀ donor-acceptor dyad adsorbed on nanocrystalline semiconductor SnO₂ electrodes has been carried out. The results show that the incident photon-to-current conversion efficiency of dyad-based photoelectrochemical cells is ∼10%.     

Stability of microcrystalline silicon solar cells with HWCVD buffer layer

Microcrystalline silicon solar cells deposited by VHF-PECVD with or without HWCVD grown p/i interface buffer layer were investigated. We studied long-term stability under storage in ambient atmosphere and performed light soaking experiments. Cells with i-layers covering a wide range of crystalline volume fractions were studied. All cells were stable or degraded slightly after storage for 2 years in air, regardless of crystalline volume fraction or presence of p/i buffer interface. Upon light soaking all cells show efficiency degradation to more or less extent depending on crystal volume fraction of the i-layer and the presence of the buffer layer: the solar cell with high crystal volume fraction are nearly stable, cells with high amorphous volume fraction degrade by up to 20%. The solar cell with HWCVD buffer layer shows better stability in the high efficiency range of relative efficiency degradation typically less than 10% after 1000 h AM 1.5 light soaking. The efficiency degradation is mainly caused by Voc and FF deterioration while Jsc is almost stable.     

Quantitative photoelectrochemical detection of biological affinity reaction: biotin-avidin interaction

Quantitative detection of a biological affinity reaction, the biotin/avidin recognition, was achieved using our newly developed photoelectrochemical analytical system. The system is based on the operation mechanism of the well-developed dye-sensitized photoelectrochemical solar cells and comprises a ruthenium tris(2,2'-bipyridine) (Ru-bipy) derivative as the photoelectrochemical signal-generating molecule, oxalate as the sacrificial electron donor, and tin oxide nanoparticle as the semiconductor electrode material. To perform the affinity reaction, avidin was immobilized on SnO(2) electrode by passive adsorption. Biotin-linked bovine serum albumin (BSA) was labeled with an NHS-ester derivative of Ru-bipy. After binding of BSA to the surface-immobilized avidin through biotin, photoelectrochemical measurement was carried out in the presence of oxalate. Anodic photocurrent was turned on and off repeatedly by control of incidental light. The action spectrum of the photocurrent resembled the absorption spectrum of Ru-bipy, proving the photocurrent was generated from the metal complex. A linear relationship between photocurrent and BSA concentration was obtained in the range of 1-100 microg/mL. This is the first case of quantitative photoelectrochemical detection of a biological affinity interaction.     

Ion coordinating sensitizer for high efficiency mesoscopic dye-sensitized solar cells: influence of lithium ions on the photovoltaic performance of liquid and solid-state cells

A Li+ coordinating sensitizer, NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-bis[(triethylene glycol methyl ether) methyl ether]-2,2'-bipyridine)(NCS)2 (coded as K51), has been synthesized, and the effect of Li+ coordination on its performance in mesoscopic titanium dioxide dye-sensitized solar cells has been investigated. Fourier transform infrared spectra suggest that Li+ coordinates to the triethylene oxide methyl ether side chains on the dye molecules. With the addition of Li+ to a nonvolatile liquid electrolyte, we observe a significant increase in the photocurrent density, with only a small decrease in the open-circuit voltage, contrary to a non ion coordinating dye which displays a large drop in potential with the addition of Li+. For a solar cell incorporating an organic hole-transporter, we find the potential rises with increasing the Li+ concentration in the hole-transporter matrix. For the liquid electrolyte and solid-state cells, we obtain power conversion efficiencies of 7.8% and 3.8%, respectively, under simulated sunlight.     

Toward electrochemical resolution of two genes on one electrode: using 7-deaza analogues of guanine and adenine to prepare PCR products with differential redox activity.

The 7-deaza analogues of guanine and adenine were incorporated into polymerase chain reaction (PCR) products by substitution of the appropriate nucleotide triphosphates into the reaction. These PCR products can be immobilized on ITO electrodes and detected by catalytic cyclic voltammetry with ruthenium polypyridyl complexes. Immobilization on indium tin oxide (ITO) electrodes of 330- and 1200-base pair (bp) PCR amplicons from the E. coli dacA gene containing one or both of the 7-deazapurines was effected by precipitation from a 9:1 DMF/acetate solution. Amplicons containing the 7-deazaguanine base were detected by observing current enhancement in the cyclic voltammogram of Ru(dmb)3(3)+/2+ (dmb = 4,4'-dimethyl-2,2'-bipyridine) due to the selective oxidation of the modified base by this mediator. Oxidation of incorporated 7-deazaadenine bases in addition to native guanines gives rise to a higher current enhancement in the cyclic voltammogram of Ru(bpy)3(3)+/2+ (bpy = 2,2'-bipyridine) compared to the enhancement observed in the presence of guanine only. This strategy was employed to simultaneously detect the 330-bp sequence containing 7-deazaadenine and the 1200-bp sequence containing 7-deazaguanine on the same ITO electrode. Such a strategy may provide a means for detecting multiple genes on a single microlocation and may thereby lead to more highly multiplexed gene assays.     

Electron-transfer studies with a new flavin adenine dinucleotide dependent glucose dehydrogenase and osmium polymers of different redox potentials

A new extracellular flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase from Glomerella cingulata (GcGDH) was electrochemically studied as a recognition element in glucose biosensors. The redox enzyme was recombinantly produced in Pichia pastoris and homogeneously purified, and its glucose-oxidizing properties on spectrographic graphite electrodes were investigated. Six different Os polymers, the redox potentials of which ranged in a broad potential window between +15 and +489 mV versus the normal hydrogen electrode (NHE), were used to immobilize and "wire" GcGDH to the spectrographic graphite electrode's surface. The GcGDH/Os polymer modified electrodes were evaluated by chronoamperometry using flow injection analysis. The current response was investigated using a stepwisely increased applied potential. It was observed that the ratio of GcGDH/Os polymer and the overall loading of the enzyme electrode significantly affect the performance of the enzyme electrode for glucose oxidation. The best-suited Os polymer [Os(4,4'-dimethyl-2,2'-bipyridine)(2)(PVI)Cl](+) had a potential of +309 mV versus NHE, and the optimum GcGDH/Os polymer ratio was 1:2 yielding a maximum current density of 493 μA·cm(-2) at a 30 mM glucose concentration.     

Poly(glycidyl methacrylate-acrylonitrile)-based polymeric electrolytes for dye-sensitized solar cell applications

Poly(glycidyl methacrylate-acrylonitrile) P(GMA-AN) copolymer was synthesized and used as a polymer electrolyte in dye-sensitized solar cells (DSSCs). P(GMA-AN)-based polymer electrolyte is obtained by adding 1-methyl-3-propylimidazolium iodide (PMII) as a room temperature ionic liquid (RTIL), tetrabutylammonium iodide (TBAI), iodide (I2) as the source of redox couple (I3(-)/I(-)) in order to improve the power conversion efficiency (PCE) by addition of optimized plasticizer contents such as ethylene carbonate (EC) and propylene carbonate (PC) in an acetonitrile solvent. These polymer electrolyte results revealed that more stable photovoltaic performance such as PCE of 4.97% with enhanced short-circuit current density (J(SC), 10.42 mA/cm2) and open circuit voltage (V(OC), 0.75 V) and fill factor (FF) of 0.63 under standard light intensity of 100 mW/cm2, irradiation of AM 1.5 sunlight. It is expected that these polymer electrolyte is an attractive alternative to liquid electrolytes for the fabrication of the long term stable DSSCs.     

Solar-driven microbial photoelectrochemical cells with a nanowire photocathode

We report a self-biased, solar-driven microbial photoelectrochemical cell (solar MPC) that can produce sustainable energy through coupling the microbial catalysis of biodegradable organic matter with solar energy conversion. The solar MPC consists of a p-type cuprous oxide nanowire-arrayed photocathode and an electricigen (Shewanella oneidensis MR-1)-colonizing anode, which can harvest solar energy and bioenergy, respectively. The photocathode and bioanode are interfaced by matching the redox potentials of bacterial cells and the electronic bands of semiconductor nanowires. We successfully demonstrated substantial current generation of 200 μA from the MPC device based on the synergistic effect of the bioanode (projected area of 20 cm2) and photocathode (projected area of 4 cm2) at zero bias under white light illumination of 20 mW/cm2. We identified the transition of rate-limiting step from the photocathode to the bioanode with increasing light intensities. The solar MPC showed self-sustained operation for more than 50 h in batch-fed mode under continuous light illumination. The ability to tune the synergistic effect between microbial cells and semiconductor nanowire systems could open up new opportunities for microbial/nanoelectronic hybrid devices with unique applications in energy conversion, environmental protection, and biomedical research.     

大小颗粒混和的纳晶多孔TiO2薄膜电极的制备及其性能研究

把大小颗粒的纳晶TiO2进行混合,制备了纳晶多孔TiO2薄膜电极并应用于染料敏化太阳能电池中.研究表明,混合一定量的大颗粒纳晶,改善了纳晶多孔TiO2薄膜对染料的吸附量和薄膜电极对光的散射性能,提高了光电输出,在100mW/cm2光照条件下,染料敏化太阳能电池的光电转换效率达到5.66%.