Dye-sensitized Solar Cells Conversion Research Articles

Synergy light-trapping-enhanced solar energy conversion in DSSCs containing texture pit and silver nanoparticles

We report on an easy synthetic method, spin coating, for Surface-enhanced Raman scattering-active texture pit array dimensions with embedded silver nanoparticles, where the gap among pits can be engineered on the micro scale. The engineered nucleation sites for the texturing process can actively control the morphological properties of the photo-anode of DSSCs and effectively improve the stability of cells. By applying those distinguished photo-anodes to dye sensitized solar cells (DSSCs), a power conversion efficiency of 7.32% is obtained. The improvement of the short-circuit current density is due to enhanced optical absorption and the presence of limited electron recombination processes. These results demonstrate that engineered nucleation sites for the texturing process can actively control the morphological properties of the photo-anode of DSSCs. It incites a new approach for adjusting the morphology and structure of the photoanode of solar cells, and opens up a new way to obtain arrayed nanostructures, which can provide a significant synthesis of optically active membrane for DSSCs.

Computational Study of Cresyl Violet Covalently Attached to the Silane Coupling Agents: Application to TiO2-Based Photocatalysts and Dye-Sensitized Solar Cells

The covalent attachment of photosensitizing dyes to TiO2 using silane coupling agents (SCAs) is a promising strategy for enhancing the photocatalytic activity of TiO2-based photocatalysts and the photovoltaic conversion of dye-sensitized solar cells (DSSCs). This approach can control the geometry and orientation of the photosensitizing dye on the TiO2 surface. In this study, a density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation was carried out on cresyl violet (CV) covalently attached to SCAs with a terminal oxirane group (OTES–Cn) to reveal the influence of OTES–Cn on the geometry of the photosensitizing dyes. The potential of CV covalently attached to OTES–Cn (CV–OTES–Cn) to act as a photosensitizing dye was also analyzed. The hydroxyl group formed by the epoxy-opening reaction between CV and OTES–Cn strongly influenced the geometry of CV–OTES–Cn, which was attributed to a CH–O interaction. Additionally, TD-DFT, frontier molecular orbital and molecular electrostatic potential calculations revealed that CV–OTES–Cn has excellent optical properties and electron injection ability. In particular, the characteristics of the unbent conformation of CV–OTES–Cn are expected to contribute significantly to the photocurrent in TiO2-based photocatalysts and DSSCs. These findings enhance the understanding of the covalent attachment strategy using SCAs and contribute to improving TiO2-based photocatalysts and DSSCs.

Effects of carbon dots on ZnO nanoparticle-based dye-sensitized solar cells

ZnO nanoparticles have been assessed the effects of added carbon dots (Cdots) on the performance of photovoltaic devices: ZnO(100) and ZnO(20) with particle sizes of 94 and 20 nm, respectively, were hybridized with Cdots and characterized by current–voltage measurements under the illumination condition. The photovoltaic conversion of dye-sensitized solar cells (DSSCs) was effective for ZnO(20) superior to Zn (100) and for the incorporation of 10 wt% Cdots in the hybrid nanostructures. Moreover, when the mole ratio (ethylenediamine:citric acid) between raw materials of Cdots was 2:1, the conversion efficiency was highest (5.9%), and this value was 7 times higher than that of ZnO(20) DSSC without Cdots. Electrochemical impedance spectroscopy also showed that the charge transfer resistance property was lowest for Cdots(2:1)-hybridized ZnO(20) DSSC. It can be thus concluded that the performance of ZnO-based DSSCs is improved by the size-minimization of ZnO and the addition of adequate amount of Cdots. The effect of carbon dots was discussed based on electron transfer between ZnO and Cdots under the illumination.

New LbL‐TiO2/ZnO Compact Films to Improve Performance of Dye‐Sensitized Solar Cells

AbstractThe preparation of nanostructured thin films consisted of TiO2/ZnO bilayers (BL) and their application in dye‐sensitized solar cells (DSCs) are reported. The film was prepared by the Layer‐by‐Layer (LbL) technique using, respectively, acid and basic sols of TiO2 and ZnO nanoparticles. The particles in the sols were characterized by dynamic light scattering (DLS) and the compact morphology of the LbL films were probed by scanning electronic (SEM) and atomic force (AFM) microscopies. The photoelectrochemical parameters of DSCs with 0, 15 and 20 BL were assessed by current‐voltage (JxV) curves, incident photon‐to‐current efficiency (IPCE), electron lifetime and electrochemical impedance spectroscopy (EIS). These results revealed a significant improvement (up to 67%) on the DSC conversion efficiency promoted by LbL film underlayers, with enhancements ascribed to an efficient blocking effect preventing the FTO/I3− charge recombination and improved contact between the mesoporous‐TiO2 and the conducting substrate (FTO).

Understanding Catalytic Behavior of Co-Sn Alloy/Graphene Counter Electrode Electrocatalysts in Liquid-Junction Photovoltaic Devices

Understanding the electrocatalytic activity of counter electrode (CE) favors to tune the sluggish triiodide reduction kinetics and to compare their catalytic activities. We present here the synthesis of CoXSn1-X alloys (0 ≤ X ≤ 1) on reduced graphene oxide (RGO) under atmospheric pressure plasma without using any toxic chemical reagents. The developed materials are then applied as catalysts for the reduction of triiodide ions to iodide ions in CE of dye-sensitized solar cells (DSCs). It should be noted that the triiodide reduction reaction is one of the utmost significances in the advanced electrochemical energy conversion of DSCs. Therefore, insights into the relationship between alloy composition, electronic structure and catalytic activity should be carefully determined in this study. As the TEM measurements, CoSn nanoparticles with size in the range of 1-5 nm is successfully immobilized on the surface of RGO. Electrochemical catalytic activity performances indicate that the Co0.9Sn0.1/RGO gave the highest catalytic activity compared other electrodes which were determined by the lowest charge-transfer resistance and diffusion impedance values. Thus, the highest power conversion efficiency was obtained for the device using Co0.9Sn0.1/RGO CE. The strategy has a great promise in developing high-performance DSCs and the launched reduction rate constant having commonality in comparing the catalytic activity of CE electrocatalysts.

Excitation energy transfer from long-persistent phosphors for enhancing power conversion of dye-sensitized solar cells

Incorporation of inorganic phosphors to improve the spectral absorption range of a dye-sensitized solar cell (DSSC) is a promising strategy to enhance efficiency beyond 15%. However, only marginal improvements have been achieved so far, which is mainly due to the use of nonoptimized device architecture and the lack of understanding of the energy transfer mechanism. Here we report results of DSSCs employing long-persistence phosphor coupled to the sensitizing dye. Detailed time-resolved photoluminescence measurements suggest that excitation energy is transferred radiatively as opposed to F\orster resonance energy transfer. As a result of efficient energy transfer, large-area solar cells show a 63% increase in the photocurrent density along with a 54% increase in power conversion efficiency. In addition, the device works as a ``nighttime solar cell'' with generation of $52\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ power density in the dark. Under short-circuit conditions, the device can output 300 mV for 30 h in the dark.

Microscopic observation of dye molecules for solar cells on a titania surface.

The lateral distribution and coverage of Ru-based dye molecules, which are used for dye-sensitized solar cells (DSCs), were directly examined on a titania surface using high-resolution scanning transmission electron microscopy (STEM). The clean surface of a free-standing titania nanosheet was first confirmed with atomic resolution, and then, the nanosheet was used as a substrate. A single dye molecule on the titania nanosheet was visualized for the first time. The quantitative STEM images revealed an inhomogeneous dye-molecule distribution at the early stage of its absorption, i.e., the aggregation of the dye molecules. The majority of the titania surface was not covered by dye molecules, suggesting that optimization of the dye molecule distribution could yield further improvement of the DSC conversion efficiencies.

Synergistic carbon nanotube aerogel – Pt nanocomposites toward enhanced energy conversion in dye-sensitized solar cells

3-D carbon nanotube aerogels and their composites with Pt nanoparticles have shown enhanced solar energy conversion compared to regular CNTs.

Phosphor positioning for effective wavelength conversion in dye-sensitized solar cells

In the present study, the wavelength conversion effect resulting from phosphor’s position in dye-sensitized solar cells (DSSCs) is investigated. Integrating phosphor (in particular, t-LaVO4:Dy3+ downshifting phosphor) into DSSCs enables C106-organometallic dye to generate excess electrons because of the wavelength conversion process from ultraviolet to visible light. The coupling of downshifting phosphors with ultraviolet wavelengths inside DSSCs induces increasing quantities of visible light, which can be absorbed into C106 dye; this phenomenon leads to an increase in the energy conversion efficiency of DSSCs. We observe that the wavelength conversion effect depends on the position of phosphor inside a DSSCs. The methods of introducing downshifting t-LaVO4:Dy3+ phosphor crystals onto a TiO2 film electrode and dispersing these crystals into an iodide electrolyte produce an increase in the overall solar-to-electrical energy conversion efficiency (η) to 9.6% and 9.5%, respectively, from 9.2% for DSSCs without phosphor components. DSSCs with phosphor both positioned on the TiO2 film and dispersed into the iodide electrolyte show a highly increased overall efficiency (η) of 9.9%. For this study, the correlation between phosphor positioning and the wavelength conversion effect inside a DSSCs is comparatively investigated, and we suggest that the results of this study represent the most viable strategy to maximally utilize the solar spectrum.

Low-cost and flexible poly(3,4-ethylenedioxythiophene) based counter electrodes for efficient energy conversion in dye-sensitized solar cells

A roll-to-roll slot die coating process was used to deposit PEDOT:PSS on PET and the resulting composite films were evaluated for use as counter electrodes in dye-sensitized solar cells (DSCs). The effect of depositing an additional layer of electropolymerized PEDOT onto the flat PEDOT/PET electrodes was also studied. Counter electrodes and complete DSCs were characterized by steady-state current–voltage, electrochemical impedance spectroscopy and IPCE measurements. Evidence that the PEDOT-based counter electrode can modify the electrolyte solution composition, probably by increasing the proton concentration, is presented. The overall cell performance under 1 Sun illumination is improved by addition of an electropolymerized layer of PEDOT to flat PEDOT/PET counter electrodes, but both remain inferior to platinized FTO. Under 0.2 Sun illumination, devices employing counter electrodes with electropolymerized PEDOT on a PEDOT/PET substrate (named as EP/PEDOT/PET) perform almost similarly to those with platinized FTO counter electrodes, suggesting that EP/PEDOT/PET electrodes may be useful in DSCs designed for low light (e.g. indoor) operation, especially considering the low costs of PEDOT and the roll-to-roll and electropolymerization processes.

Effects of Ion Doping on the Optical Properties of Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSC) play a leading role in the third generation photovoltaics due to their low cost, easy fabrication process, high conversion efficiency and good stability. As a media of dye adsorption, electron transport, and electrolyte diffusion, the nanocrystalline semiconductor photoanode plays a key role during light-to-electricity conversion in DSC. This paper studies the influence of different ions doping and different concentration of ion doping on the electrical and optical properties of DSC, through the photoelectric property test of DSC. We learn that Zn2+ doped TiO2 photoanode is the best. At the same time there was an optimum doping concentration which was 0.05% (mole fraction).

Enhanced performance of dye-sensitized solar cells using gold nanoparticles modified fluorine tin oxide electrodes

We have investigated plasmon-assisted energy conversion in dye-sensitized solar cells (DSCs) applying gold nanoparticles (NPs) modified fluorine tin oxide (FTO) electrodes. A series of Au NPs with different sizes (15–80 nm) were synthesized and immobilized onto FTO glass slides. Photoanodes were prepared on these Au modified FTO substrates using P25 TiO2 powders and by the screen-printing method. The size effects of Au NPs on the photovoltaic performance of the formed DSCs were investigated systematically. Structural and photoelectrochemical properties of the formed photoanodes were examined by field emission scanning electron microscopy and electrochemical impedance spectroscopy. It was found that the energy conversion efficiency of the DSC was highly dependent on the Au particle size. When the particle size was not greater than 60 nm, the DSC based on the Au NP-FTO composite electrode showed a higher short-circuit current density and better photovoltaic (PV) performance than the cell based on the bare FTO. The best cell was achieved using 25 nm sized Au NPs modified FTO. It exhibited a conversion efficiency of 6.69%, which was 15% higher than that of DSCs without Au NPs. The related PV performance enhancement mechanisms, photoelectrochemical processes and surface-plasmon resonances in DSCs with Au nanostructures are analysed and discussed.

Microstructural and chemical variation of TiO2 electrodes in DSSCs after ethanol vapour treatment

TiO2 based dye-sensitized solar cells (DSSCs) have great potential to solve many energy challenges, however, their low energy conversion rate is still a barrier for further applications. Ethanol vapour post-treatment can improve the DSSC's conversion efficiency without changing its architecture, and a stable 2–3% improvement was found in our experiments. Microstructural and chemical factors were investigated using scanning electron microscopy and analytical electron microscopy on treated and untreated electrodes. The vapour treatment improved the porosity and surface-to-volume ratio of the TiO2 particles, decreased electron transport loss between TiO2 and fluorine doped tin oxide, and increased hydroxyl sites on the TiO2 particle's surface. The modification therefore enhanced the dye uptake and dye–TiO2 coupling, and it reduced the energy loss during the carrier transfer.

Enhancement of Near-IR Photoelectric Conversion in Dye-Sensitized Solar Cells Using an Osmium Sensitizer with Strong Spin-Forbidden Transition.

A new osmium (Os) complex of the [Os(tcterpy)-(4,4'-bis(p-butoxystyryl)-2,2'-bipyridine)Cl]PF6 (Os-stbpy) has been synthesized and characterized for dye-sensitized solar cells (DSSCs). The Os-stbpy dye shows enhanced spin-forbidden absorptions around 900 nm. The DSSCs with Os-stbpy show a wide-band spectral response up to 1100 nm with high overall conversion efficiency of 6.1% under standard solar illumination.

Investigation on the energy conversion of dye-sensitized solar cells based on TiO2 core/shell using metal oxide as a barrier layer

Photo-electrochemical solar cells based on a core-shell structure including ZnO shell and TiO2 cove, have been fabricated with ruthenium bipyridyl complex (N719) as the sensitizer. Compared with the pure anatase TiO2, the ZnO-covered TiO2 film possesses outstanding ability to transport electrons with an overall power conversion efficiency of 3.72. Elctrochemical study shows that surface modification of TiO2 film with ZnO can increase the concentration of free electrons in the conduction band of TiO2. This remit implies that the charge recombination is reduced in process of electron transport through the TiO2 porous film, which can decrease the photocurrent loss and hence improve Dye-Sensitized solar ceils (DSSCs) efficiency. This result indicates that optimization of TiO2 porous network fabrication condition is efficient, for the improvement of TiO2 based DSSC’s performances.

A Convenient Route to High Area, Nanoparticulate TiO2 Photoelectrodes Suitable for High-Efficiency Energy Conversion in Dye-Sensitized Solar Cells

Ethanol-soluble amphiphilic TiO(2) nanoparticles (NPs) of average diameter ∼9 nm were synthesized, and an α-terpineol-based TiO(2) paste was readily prepared from them in comparatively few steps. When used for fabrication of photoelectrodes for dye-sensitized solar cells (DSSCs), the paste yielded highly transparent films and possessing greater-than-typical, thickness-normalized surface areas. These film properties enabled the corresponding DSSCs to produce high photocurrent densities (17.7 mA cm(-2)) and a comparatively high overall light-to-electrical energy conversion efficiency (9.6%) when deployed with the well-known ruthenium-based molecular dye, N719. These efficiencies are about ∼1.4 times greater than those obtained from DSSCs containing photoelectrodes derived from a standard commercial source of TiO(2) paste.

Co-sensitization with near-IR absorbing cyanine dye to improve photoelectric conversion of dye-sensitized solar cells

Two carboxylated cyanine dyes, 3-butyl-2-[3-(1-butyl-5-carboxy-1,3-dihydro-3,3-dimethyl-2H-indol-2-ylidene)-1-propen-1-yl]-1,1-dimethyl-7-[1-[2-[6-(4-morpholinyl)-1,3-dioxo-1H-benz[ de]isoquinolin-2(3H)-yl]ethyl]-1H-1,2,3-triazol-4-yl]-1H-Benz[ e]indolium iodide (A), 2-[5-(1-butyl-5-carboxy-1,3-dihydro-3,3-dimethyl-2H-indol-2-ylidene)-1,3-pentadienyl]-3-ethyl-1,1-dimethyl-1H-Benz[ e]indolium iodide (B), have been prepared and their photophysical and electrochemical properties have been investigated. A, B and their mixtures (AB) were used as sensitizers in nanocrystalline TiO 2 solar cells to improve photoelectric conversion efficiency. It was found that the solar cell sensitized with A3B1 (molar ratio: A:B = 3:1) generated a high power conversion efficiency of 3.0% under AM1.5G illumination (100 mW cm −2), indicating that co-sensitization is a promising method to improve the photoelectrical properties of dye-sensitized solar cells.

Novel Nanostructured Photoelectrodes - Electrodeposition of Metal Oxides onto Transparent Conducting Oxide Nanofibers

AbstractNanostructured metal oxides with high surface areas have been shown to be efficient photoelectrodes for light-to-energy conversion in dye-sensitized solar cells (DSCs). In this work we demonstrate the use of nanofibrous mats of transparent conducting oxides (TCOs) as nanostructured electrodes, especially for DSCs. The nanofibers have been obtained by electrospinning suitable inorganic precursors and polymers, followed by calcination to remove the polymer. Afterwards, TiO2 layers were generated on our 3D-electrodes by electrodeposition. An improved performance as DSC was found compared to flat electrodes of similar thickness, validating our approach.