High-performance Dye-sensitized Solar Cells Research Articles

Amino acid assisted synthesis of mesoporous TiO2 nanocrystals for high performance dye-sensitized solar cells

Mesoporous TiO2 nanocrystals (denoted as TiO2-MS) have been synthesised by a one-step amino acid assisted synthesis method using L-lysine as a catalyst. An ∼18% enhancement in dye-sensitized solar cells’ (DSSCs) conversion efficiency was achieved using the TiO2-MS as photoanodes compared to that of benchmark Degussa P25 TiO2. The improved dye loading capacity and reduced charge recombination of TiO2-MS are responsible for the enhanced performance.

Transparent flexible Pt counter electrodes for high performance dye-sensitized solar cells

A transparent flexible Pt counter electrode (CE) was prepared on indium tin oxide–polyethylene naphthalate film using a simple dip coating method for dye-sensitized solar cells (DSCs), and a high catalytic activity was achieved. The DSC using this transparent flexible CE gave a power conversion efficiency (PCE) of 6.95% with front illumination, and a PCE of 5.18% with rear illumination.

Efficient light-scattering functionalized TiO2 photoanodes modified with cyanobiphenyl-based benzimidazole for dye-sensitized solar cells with additive-free electrolytes

Light-scattering functionalized cyanobiphenyl-based benzimidazole was synthesized and applied in the surface modification of dyed TiO2 photoanodes for dye-sensitized solar cells (DSSCs). DSSCs based on the ionic liquid and all-solid-state electrolytes were fabricated and characterized, without the addition of additives in the electrolytes. Compared with electrolytes containing the additive N-butylbenzimidazole (NBB), surface modification of dyed TiO2 photoanodes with cyanobiphenyl-based benzimidazole could enhance the values of the open-circuit photovoltage (Voc), short-circuit photocurrent density (Jsc) and the overall PCE of the fabricated DSSCs, due to the suppressed charge recombination rate, the conductivity optimization of the electrolytes and enhanced light harvesting capability at the TiO2 photoanode/electrolyte interface. Under the simulated air mass 1.5 solar spectrum illuminations at 100 mW cm−2, the fabricated devices achieved a cell efficiency of ∼6.63% and ∼5.82% for ionic liquid and all-solid-state electrolytes, respectively. These results provide an alternative strategy for high performance DSSCs with additive-free electrolytes.

High-performance dye-sensitized solar cells based on 5,6-bis-hexyloxy-benzo[2,1,3]thiadiazole

New dipolar compounds containing a 5,6-bis-hexyloxy-benzo[2,1,3]thiadiazole entity in the conjugated spacer between the electron donating arylamine and the electron accepting 2-cyanoacrylic acid have been synthesized. These compounds were used as the sensitizers for efficient dye-sensitized solar cells. Compared to the congeners without the hexyloxy chains, the new dyes effectively suppress the dark currents and significantly improve the cell performance. The best conversion efficiency reached ∼92% of the N719-based standard DSSC fabricated and measured under similar conditions (AM 1.5 irradiation).

High-performance dye-sensitized solar cells based on hierarchical yolk–shell anatase TiO2beads

Yolk–shell TiO2 beads consisting of nanoparticles are synthesized by using a facile hydrothermal method. The influences of hydrothermal reaction temperature on the size of TiO2 particles and the photovoltaic performance of dye-sensitized solar cells (DSSCs) have been investigated in detail. A DSSC based on the yolk–shell TiO2 bead photoelectrode (∼15 μm) exhibits an energy conversion efficiency of 9.05%, which is much higher than that of P25 (7.56%). This can be mainly attributed to the fast electron transport and long electron lifetime resulting in a larger electron diffusion coefficient and higher charge collection efficiency for the former, which are confirmed by intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS). In addition, the superior light scattering ability of hierarchical yolk–shell TiO2 beads compared to P25 film measured by UV-vis diffuse spectrum also contributes to higher photocurrent and photovoltaic performance.

High-performance dye-sensitized solar cells based on PEDOT nanofibers as an efficient catalytic counter electrode

Poly(3,4-ethylenedioxythiophene) nanofibers (PEDOT-NFs) with 10–50 nm diameters and high electrical conductivity (up to 83 S cm−1) have been fabricated chemically within micelles composed of sodium dodecyl sulfate (SDS) as nanoreactors. Dimethyl sulfoxide (DMSO, 5 wt%) was added to a methanol-based colloidal dispersion containing PEDOT-NFs to improve dispersibility. The dye-sensitized solar cells (DSSCs) using PEDOT-NFs as a counter electrode (CE) with low surface resistance and a highly porous surface exhibited enhanced power conversion efficiency (9.2%) compared to bulk PEDOT (6.8%). To date, PEDOT-NFs have shown the highest performance among CEs using PEDOT. It also surpassed the efficiency of platinum (Pt) CEs (8.6%). Electrochemical characterization, such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), showed that PEDOT-NFs efficiently reduced triiodide due to the enhanced electrical and morphological properties, which contributed to the high current density (17.5 mA cm−2) and fill factor (72.6%).

Thermoelectric Bi2Te3-improved charge collection for high-performance dye-sensitized solar cells

A new dye-sensitized solar cell based on a thermoelectric Bi2Te3/TiO2 composite anode is demonstrated, in which the incorporated Bi2Te3 nanoplates function as built-in nanoscale electron generators to convert “waste heat” to electricity and as a good photoreaction catalyst to enhance the charge transfer rate, resulting in 28% improvement of the overall power conversion efficiency.

Iodide-functionalized graphene electrolyte for highly efficient dye-sensitized solar cells

1-Octyl-2,3-dimethylimidazolium iodide, ODI, was used as an electron acceptor to functionalize graphene to impart electrocatalytic activity for triiodide reduction in dye-sensitized solar cells (DSSCs). Raman and X-ray photoelectron spectroscopic measurements identified the graphene formation from graphene oxide with ODI. The resultant graphene positively charged via an intermolecular charge-transfer process with ODI showed remarkable electrocatalytic activity toward triiodide reduction. The inner work mechanism of solar cell devices was analyzed by intensity-modulated photovoltage spectroscopy, by intensity modulated photocurrent spectroscopy, and through an analysis of photovoltage transients. The results indicated that ODI-graphene electrolyte provides effective intermolecular charge transfer, thus making it feasible for use in the creation of high-performance DSSC devices.

Layer‐by‐Layer Formation of Block‐Copolymer‐Derived TiO2 for Solid‐State Dye‐Sensitized Solar Cells

Morphology control on the 10 nm length scale in mesoporous TiO(2) films is crucial for the manufacture of high-performance dye-sensitized solar cells. While the combination of block-copolymer self-assembly with sol-gel chemistry yields good results for very thin films, the shrinkage during the film manufacture typically prevents the build-up of sufficiently thick layers to enable optimum solar cell operation. Here, a study on the temporal evolution of block-copolymer-directed mesoporous TiO(2) films during annealing and calcination is presented. The in-situ investigation of the shrinkage process enables the establishment of a simple and fast protocol for the fabrication of thicker films. When used as photoanodes in solid-state dye-sensitized solar cells, the mesoporous networks exhibit significantly enhanced transport and collection rates compared to the state-of-the-art nanoparticle-based devices. As a consequence of the increased film thickness, power conversion efficiencies above 4% are reached.

High performance dye-sensitized solar cells based on platinum nanoparticle/multi-wall carbon nanotube counter electrodes: The role of annealing

A composite film is coated on the FTO using a solution, containing a synthesized dispersant, poly(oxyethylene)-segmented imide (POEM), dihydrogen hexachloroplatinate (H 2PtCl 6), and multi-wall carbon nanotube (MWCNT); the thus coated FTO is used as the counter electrode (CE) for a dye-sensitized solar cell (DSSC). The annealing temperature of the composite film, in the range of 110–580 °C, is found to be crucial for optimizing its catalytic ability to obtain the best possible performance for the DSSC. About 47% loss in mass for the POEM/H 2PtCl 6/MWCNT composite is observed from 110 to 390 °C, due to not only the progressive formation of PtNPs from H 2PtCl 6 but the decomposition of POEM. Therefore, the efficiencies ( η) of DSSCs applying these CEs are enhanced from 1.28 ± 0.08% (110 °C) to 8.47 ± 0.21% (390 °C). The mass of the composite loses dramatically under heating above 390 °C, due to the decomposition of MWCNTs. The η decreases to 7.77 ± 0.15% at 450 °C because the decrease in surface roughness of film. PtNPs grow in sizes from 450 to 580 °C, resulting in the further decrease in catalytic ability of film and the observed η from 7.77 ± 0.15% to 7.19 ± 0.21%.

Highly Efficient Organic Photosensitizer with Dinaphthylphenylamine Unit as a Donor for DSSCs

E-mail: chk@inha.ac.krReceived August 29, 2011, Accepted September 19, 2011Key Words : DSSCs, Dye-sensitized solar cells, High efficiency, DinaphthylphenylamineRecently, dye-sensitized solar cells (DSSCs) have at-tracted great attention because they have advantages inconverting solar energy to electrical energy at low cost. Oneof the key issues in high performance DSSCs is the rationaldesign of the photosensitizers, which can exhibit high solar-to-energy conversion efficiency. The Ru complex photo-sensitizers such as N3, N719 and Black dye exhibit effi-ciencies about 11% under AM 1.5G irradiation.

Enhancement of the efficiency of dye-sensitized solar cell with multi-wall carbon nanotubes/polythiophene composite counter electrodes prepared by electrodeposition

For the purpose of increasing the energy conversion efficiency of dye-sensitized solar cells (DSSCs), multi-wall carbon nanotube (MWCNT)/polythiophene (PTh) composite film counter electrode has been fabricated by electrophoresis and cyclic voltammetry (CV) in sequence. The morphology and chemical structure have been characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and Raman spectroscopy respectively. The overall energy conversion efficiency of the DSSC employing the MWCNT/PTh composite film has reached 4.72%, which is close to that of the DSSC with a platinum (Pt) counter electrode (5.68%). Compared with a standard DSSC with MWCNT counter electrode whose efficiency is 2.68%, the energy conversion efficiency has been increased by 76.12% for the DSSC with MWCNT/PTh counter electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I 3 − reduction can potentially be used as the counter electrode in a high-performance DSSC.

Flexible Counter Electrodes Based on Mesoporous Carbon Aerogel for High-Performance Dye-Sensitized Solar Cells

Flexible counter electrodes (CEs) are designed and fabricated by depositing the composite film of carbon materials (carbon aerogel, carbon black, and active carbon) and poly(tetrafluoroethylene) on stainless steel mesh and applied in dye-sensitized solar cells (DSSCs). The effect of pore structure of the carbon materials on the electrocatalytic activity was investigated by cyclic voltammogram and electrochemical impedance spectroscopic analysis. The carbon aerogel with a mesopore structure showed the highest double-layer capacitance and best electrocatalytic activity. The DSSC, based on the carbon aerogel CE and a ruthenium dye (N719), showed a high power conversion efficiency of 9.06%, which is 99% of that based on a Pt CE (9.14%) under the same experimental conditions.

Organic Dyes Containing a Coplanar Indacenodithiophene Bridge for High-Performance Dye-Sensitized Solar Cells

A series of new organic dyes exploiting coplanar indacenodithiophene as the central π-spacer of the classical donor-(π-spacer)-acceptor configuration were synthesized and characterized for dye-sensitized solar cells. The coplanarity of the indacenodithiophene core facilitates efficient donor to acceptor charge transfer, imparting the new organic dyes significant bathochromic shifts and remarkable power conversion efficiencies of up to 6.7% (DTInDT) under AM 1.5G radiation.

Layer-by-Layer Fabrication of Multiple-Dye-Sensitized TiO<SUB>2</SUB> Films for Dye-Sensitized Solar Cells by Vacuum Cold Spray

Space-separate co-sensitization allows a more flexible design of dye sensitizers and promotes the development of high performance dye-sensitized solar cells, since the negative interactions between different dyes are minimized by the spatial seperation. The key point involves depositing nano-TiO particles on the dye-loaded TiO layer to form an efficient electron transport between the outer TiO layer and the inner dye-loaded layer. Layer-by-layer fabrication of multiple-dye-sensitized TiO films was realized through high velocity impact deposition by vacuum cold spray. Results show that the effective connection between the nano-TiO particles in the outer layer and the inner dyeloaded layer was realized through the high compressive pressure pulses resulting from the high velocity particle impact on deposit surface. It is found that the photovoltaic performance of the inner dye-loaded photoanode was not influenced by the deposition of the outer layer. A significant enhancement of photocurrent was obtained by space-separate co-sensitization of N719 dye and Black dye due to the effective connection between the outer layer and the inner dye-loaded layer.

Characterization of TiO2Nanocrystalline Films for High Performance Dye-Sensitized Solar Cells

Titanium dioxide (TiO2) thin films were deposited by the sol-gel method with a surfactant-assisted mechanism. Its application for dye-sensitized solar cells (DSSCs) was investigated. Brunauer-Emmett-Teller, X-ray diffraction and field emission scanning electron microscopy techniques were used to characterize the surface characteristics of thin films. Photovoltaic-current density measurements were performed to determine the photoelectrochemical properties of the thin films and the performance of DSSCs. Energy conversion efficiency of about 6.1% was achieved for cells with conductive glass under illumination with AM 1.5 (100 mWcm -2 ) simulated sunlight. Investigation showed higher photo-energy conversion efficiency for mesoporous TiO 2 nanocrystalline films used in DSSCs relative to commercially available Degussa P25 films

Electron Mobility and Injection Dynamics in Mesoporous ZnO, SnO2, and TiO2 Films Used in Dye-Sensitized Solar Cells

High-performance dye-sensitized solar cells are usually fabricated using nanostructured TiO(2) as a thin-film electron-collecting material. However, alternative metal-oxides are currently being explored that may offer advantages through ease of processing, higher electron mobility, or interface band energetics. We present here a comparative study of electron mobility and injection dynamics in thin films of TiO(2), ZnO, and SnO(2) nanoparticles sensitized with Z907 ruthenium dye. Using time-resolved terahertz photoconductivity measurements, we show that, for ZnO and SnO(2) nanoporous films, electron injection from the sensitizer has substantial slow components lasting over tens to hundreds of picoseconds, while for TiO(2), the process is predominantly concluded within a few picoseconds. These results correlate well with the overall electron injection efficiencies we determine from photovoltaic cells fabricated from identical nanoporous films, suggesting that such slow components limit the overall photocurrent generated by the solar cell. We conclude that these injection dynamics are not substantially influenced by bulk energy level offsets but rather by the local environment of the dye-nanoparticle interface that is governed by dye binding modes and densities of states available for injection, both of which may vary from site to site. In addition, we have extracted the electron mobility in the three nanoporous metal-oxide films at early time after excitation from terahertz conductivity measurements and compared these with the time-averaged, long-range mobility determined for devices based on identical films. Comparison with established values for single-crystal Hall mobilities of the three materials shows that, while electron mobility values for nanoporous TiO(2) films are approaching theoretical maximum values, both early time, short distance and interparticle electron mobility in nanoporous ZnO or SnO(2) films offer considerable scope for improvement.

High-Performance Dye-Sensitized Solar Cells with Gel-Coated Binder-Free Single-Walled Carbon Nanotube Films as Counter Electrode

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Surface Treatment of TiO2Electrode for Dye-Sensitized Solar Cells Using Low-Temperature and Low-Energy Dielectric Barrier Discharge in Air

A low-temperature and low-energy plasma surface treatment of nanoporous titanium oxide (TiO2) electrode for dye-sensitized solar cells (DSCs) is proposed using pulsed dielectric barrier discharge (DBD) under room air condition. When the treatment time is 10 min with the discharge voltage at 21.5 kV, the short-circuit current and the energy conversion efficiency are increased by 10% by the DBD treatment. The DBD treatment has advantages over previously studied plasma treatments of the TiO2 electrode of DSCs using a plasma jet or a low-pressure O2 plasma: (i) it requires no gas flow and no vacuum equipment, (ii) it is low-temperature treatment causing no damage on glass and plastic substrates, and (iii) it requires only a very low energy consumption. The DBD treatment is simple and cost-effective, having a strong potential for promoting the development of high-performance DSCs.

Surface Treatment of TiO2 Electrode for Dye-Sensitized Solar Cells Using Low-Temperature and Low-Energy Dielectric Barrier Discharge in Air

A low-temperature and low-energy plasma surface treatment of nanoporous titanium oxide (TiO2) electrode for dye-sensitized solar cells (DSCs) is proposed using pulsed dielectric barrier discharge (DBD) under room air condition. When the treatment time is 10 min with the discharge voltage at 21.5 kV, the short-circuit current and the energy conversion efficiency are increased by 10% by the DBD treatment. The DBD treatment has advantages over previously studied plasma treatments of the TiO2 electrode of DSCs using a plasma jet or a low-pressure O2 plasma: (i) it requires no gas flow and no vacuum equipment, (ii) it is low-temperature treatment causing no damage on glass and plastic substrates, and (iii) it requires only a very low energy consumption. The DBD treatment is simple and cost-effective, having a strong potential for promoting the development of high-performance DSCs.