Durability Of Dye-sensitized Solar Cells Research Articles

Performance enhancement of aqueous dye-sensitized solar cells via introduction of a quasi-solid-state electrolyte with an inverse opal structure

To bridge the gap in the power conversion efficiencies (PCEs) of aqueous and organic-solvent based dye-sensitized solar cells (DSCs), water-based electrolytes are exploited for a new role to enhance DSC performance. Hydrogels with an inverse opal structure (IOS) were prepared using various SiO2 opal films as templates. The gels were further used as a host for preparing fully water-based gel electrolytes with a photonic band gap (PBG) on which quasi-solid-state DSCs were fabricated. The current–voltage curves indicate that PCEs for the gel electrolytes with the IOS are superior to those for the reference gel electrolyte without the structure, and a maximum average PCE of 1.80% is achieved for the gel electrolytes with the PBG around 624nm, which is approximately 22% higher than the value for the reference gel electrolyte (1.48%). The action spectra reveal increases of the incident photo-to-current conversion efficiencies both in and beyond the PBG region, indicating that the back reflection and scattering of photons as a result of the IOS are significant for light-harvesting and PCE enhancement. The electrochemical impedance spectra further demonstrate that the IOS lowers the Warburg impedance and the resistance at the TiO2/electrolyte interface compared to the reference gel electrolyte. Furthermore, the durability of DSCs is improved by the gel electrolyte/TiO2 interface and the IOS.

Improved durability of dye-sensitized solar cell with H2-reduced carbon counter electrode

Carbon counter electrodes for dye-sensitized solar cells (DSSCs) have attracted strong attention due to their low material cost and practically high power conversion efficiency (PCE). However, there were issues in PCE stability observed during durability tests. In this study, H2-reduced carbon counter electrode for low cost DSSCs is introduced and demonstrated improved durability over the conventional carbon electrodes, with the absolute PCE value of 7.7%. It was found that carbon resistance decay ratio improved compared to those without H2-reduction process. These cells after the durability test were disassembled, and surface adsorptions on the carbon counter electrodes were analyzed. The adsorption of compounds originated from the dye and co-adsorbents on the H2-reduced carbon electrode was largely reduced, due to the cleaning of surface functional groups that can adsorb large molecules. These results suggest that H2-reduction process proposed in this work effectively reduces surface adsorptions on carbon electrode, and as a result improves the durability of DSSCs.

Synthesis of POSS-based ionic conductors with low glass transition temperatures for efficient solid-state dye-sensitized solar cells.

Replacing liquid-state electrolytes with solid-state electrolytes has been proven to be an effective way to improve the durability of dye-sensitized solar cells (DSSCs). We report herein the synthesis of amorphous ionic conductors based on polyhedral oligomeric silsesquioxane (POSS) with low glass transition temperatures for solid-state DSSCs. As the ionic conductor is amorphous and in the elastomeric state at the operating temperature of DSSCs, good pore filling in the TiO2 film and good interfacial contact between the solid-state electrolyte and the TiO2 film can be guaranteed. When the POSS-based ionic conductor containing an allyl group is doped with only iodine as the solid-state electrolyte without any other additives, power conversion efficiency of 6.29% has been achieved with good long-term stability under one-sun soaking for 1000 h.

Surface passivation: The effects of CDCA co-adsorbent and dye bath solvent on the durability of dye-sensitized solar cells

The long-term stability of dye-sensitized solar cells (DSCs) based on an amphiphilic ruthenium sensitizer, CYC-B6L was studied. When the surface of the TiO2 electrode was passivated with a co-adsorbent, chenodeoxycholic acid (CDCA), the resulting DSC reveals very good long-term stability with over 87% of initial performance under a 1000h prolonged light-irradiation and thermal stress (60°C) aging, which is as good as the state-of-the art robust device. The solvent used in dye bath also affects the long-term stability of the DSC devices. The effect of co-adsorbent and the impact of the dye bath solvents on the device durability were investigated using the electrochemical impedance spectroscopy.

Enhanced photovoltaic performance and long-term stability of dye-sensitized solar cells by incorporating SiO2 nanoparticles in binary ionic liquid electrolytes

Hydrophilic SiO2 nanoparticles in a binary ionic liquid (bi-IL) consisting of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium dicyanimide (EMIDCA) facilitated electron transfer and solidified the electrolyte for a dye-sensitized solar cell (DSC). We investigated the dependence of charge transport and photovoltaic performance on the composition of bi-IL electrolytes with varied ratio of SiO2 nanoparticles. The electrochemical impedance spectra revealed a decreased resistance to charge transfer at the Pt counter electrode (Rct1) when SiO2 (up to 2.0wt.%) was added, improving the photovoltaic parameters. The DSC based on a TiO2 nanocrystalline film (thickness 14.2μm) with a composite ionic gel electrolyte of EMIDCA/PMII bi-IL (33vol.% of EMIDCA) incorporating SiO2 (2wt.%) exhibited a power conversion efficiency of 5.28% under simulated solar illumination (AM 1.5G, 100mWcm−2). The durability of DSC with a SiO2 solidified electrolyte was superior to that of a liquid one, exhibiting good stability at 60°C in darkness during an accelerated test for 1000h.

Fabrication of Monolithic Dye-Sensitized Solar Cell Using Ionic Liquid Electrolyte

To improve the durability of dye-sensitized solar cells (DSCs), monolithic DSCs with ionic liquid electrolyte were studied. Deposited by screen printing, a carbon layer was successfully fabricated that did not crack or peel when annealing was employed beforehand. Optimized electrodes exhibited photovoltaic characteristics of 0.608 V open-circuit voltage, 6.90 cm−2 mA short-circuit current, and 0.491 fill factor, yielding 2.06% power conversion efficiency. The monolithic DSC using ionic liquid electrolyte was thermally durable and operated stably for 1000 h at 80°C.

Dye-Sensitized Solar Cells Using Surface-Stabilized Nanocrystalline-TiO 2 Electrodes Coated by Epoxy Polymer

In order to improve the thermal durability of dye-sensitized solar cells, epoxy polymer was coated on dyed-TiO 2 electrode to prevent dye desorption under heating condition over 80 °C. The covering effect on epoxy polymer was confirmed using impedance spectroscopy. Using the epoxy polymer coating with Z907 Ru dye and ionic liquid electrolyte, the DSC photovoltaic durability was improved up to 90 °C, which is the highest temperature published for the DSC durability test. Although the epoxy polymer suppressed the DSC photovoltaic effect, it enhance the thermal durability; DSC coated epoxy polymer on the dyed-TiO 2 electrode was able to prolong the efficiency over 90% of the initial value at 90 °C for 550 hours. Key words: Dye-sensitized solar cells; Epoxy polymer; Ionic liquid electrolyte; Thermal durability; Heat test

Water Contamination Effect on Liquid Acetonitrile/TiO2 Anatase (101) Interface for Durable Dye-Sensitized Solar Cell

We have investigated the structural and electronic properties of liquid acetonitrile (MeCN)/TiO2 anatase (101) interfaces involving a water molecule in order to analyze effect of ubiquitous water contamination in the typical electrolyte solution on the durability of dye-sensitized solar cell (DSSC), by using density-functional molecular dynamics simulations at room temperature. Our results show that H2O does not dive into the unbound Ti5C sites on the (101) surface kinetically, once the coverage of MeCN is saturated (Θ ≈ 0.6). However, H2O adsorption through hydrogen bond with surface O2C sites, not a Ti5C site, is found the most stable if MeCN solvent is introduced to H2O-preadsorbed TiO2 anatase (101) surface. This no-adsorption character of Ti5c site in the aprotic solvent MeCN is in stark contrast to the case where the (101) surface is immersed by H2O layer or liquid H2O. The adsorbed H2O molecule via the hydrogen bond between O2C and HW has its 1b1 orbital at an energy just below the valence band maximum of TiO2. Therefore, this H2O has a sufficient possibility to become a cation radical by capturing hole generated by irradiation, which may attack the dye molecules toward the desorption. We thus demonstrate that removing H2O from the anatase (101) surface prior to introduction of the MeCN electrolyte solution is crucial to make the DSSCs more durable and efficient.

Improving the durability of dye-sensitized solar cells through back illumination

Highly efficient and stable back illumination dye-sensitized solar cell (BIL-DSSC) is developed using its Pt-counter electrode (Pt-CE) as the light-irradiating surface. Photovoltaic parameters are measured for DSSCs with Pt-CEs obtained with different sputtering periods of platinum layer. By optimizing the transmittance and catalytic property of the platinum layer on the counter electrode, a light-to-electricity conversion efficiency ( η) of 7.54% is achieved with back illumination at 100 mW cm −2, when the platinum deposition time is 30 s. The effects of platinum layers with different sputtering periods on the photovoltaic characteristics of the respective DSSCs are explained in terms of transmittance and catalytic activity of the layers. A comparative study is also made on the durability of the DSSCs with BIL and front illumination (FIL), in which the respective DSSCs are previously subjected to UV-soaking for different periods of time under simulated conditions of back and front illuminations; at-rest stability tests for such UV-soaked DSSCs carried out through BIL and FIL suggest a far higher stability in favor of the BIL-DSSC, compared to that of the FIL-DSSC. Explanations are substantiated with transmittance spectra, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and absorption spectra.

Durability of Dye-Sensitized Solar Cells and Modules

It was investigated that the intrusion of water into the electrolyte was the most critical reason for the low stability of a dye-sensitized solar cell. To prevent the water intrusion, robust solar cells and submodules with a novel protection layer of metal circuit and tightly sealing package was developed. The excellent stability of the cell with ionic liquid electrolyte at high temperature conditions was also reveled. The resulting cell employing noble construction and ionic liquid electrolyte showed an extremely high stability to pass several endurance tests standardized in JIS for the stability of the photovoltaic submodule.

Long-term durability and degradation mechanism of dye-sensitized solar cells sensitized with indoline dyes

Long-term durability and degradation mechanism of dye-sensitized solar cells (DSC) sensitized with organic dyes was studied with a yellow indoline dye (D131). Durability of DSC using D131 depended on electrolyte composition. The degradation mechanism of D131 were studied by model reaction in the organic solvent. Major degradation product was identified as decarboxylated D131 (DC131), and it was found that degradation was promoted by iodine and/or amine in the electrolyte. Analysis of degradation product in actual degraded cells showed that DC131 was produced in the cell. DSC with optimized electrolyte exhibited good outdoor stability over several months.

Dye-sensitized solar cells with ionic gel electrolytes prepared from imidazolium salts and agarose

Abstract New ionic gel electrolytes, semi-solid state electrolytes comprised of ionic liquid and gelator were investigated in order to improve the durability of dye-sensitized solar cells (DSCs). The ionic gels were prepared from agarose, natural polysaccharide, and 1-alkyl-3-methyl-imidazolium salts. The gels showed sufficient mechanical strength even though a very small amount of agarose was added (1.0-1.5 wt%). The photon to electron conversion efficiency of the DSCs containing ionic gel electrolyte was 2.93% under simulated sunlight (air mass 1.5) with a light intensity of 100 mW cm−2. To cite this article: K. Suzuki et al., C. R. Chimie 9 (2006).