Improvement in long-term stability of dye-sensitized solar cell for outdoor use

To improve the intrinsic stability of the component of dye-sensitized solar cells (DSCs), we have fabricated the unit cell using solvent-free ionic liquid electrolyte. The degradation in the continuous 1 sun light soaking test at 60 °C over 15,000 h was effectively suppressed, compared with the cell using γ-butyrolactone electrolyte. The lifetime for outdoor use was estimated over 15 years from acceleration factor based on the outdoor exposure test. To confirm the stability of the DSC under practical outdoor use, we fabricated the solar light using the DSC modules, rechargeable batteries and bright light emitting diode (LED). The solar lights have been emitting a bright white light at night using the electricity from batteries charged by the DSC modules during the daytime in any weather condition for a half year.     

Improvement on the long-term stability of flexible plastic dye-sensitized solar cells

We investigate the long-term stability of performance for plastic dye-sensitized solar cells (DSSCs) based on organic iodides (TBAI or PMII) in methoxypropionitrile-based electrolytes. Plastic DSSCs containing TBAI maintain 96.9% of baseline efficiency under more than 1000 h prolonged one sun light irradiation and thermal stress (60 °C) aging. The factors of device long-term stability, such as the effects of organic iodides, cell-sealing conditions, and the sheet resistance of indium tin oxide coated polyethylene naphthalate substrate (ITO/PEN) are discussed via using electrochemical impedance spectroscopy and electrical resistance measurement.     

Portable,parallel grid dye-sensitized solar cell module prepared by screen printing

Screen-printing technology is used to fabricate large dye-sensitized solar cells (DSSCs). The high series-resistance associated with transparent conductive oxide glass substrates causes poor performance in large DSSCs especially at an exposure of 1 sun. The DSSC design has an embedded silver grid; a fluorine-doped tin oxide (FTO) glass substrate and stripe type titanium dioxide (TiO₂) active layers introduced by screen-printing. The counter electrode is prepared from a screen printable paste based on hexachloro platinic acid. A DSSC module, which consists of five stripe-type working electrodes on a 5 cm × 5 cm, embedded silver grid FTO glass substrate, shows stable performance with an energy conversion efficiency of 5.45% under standard test conditions.     

The 3-dimensional dye-sensitized solar cell and module based on all titanium substrates

Here we report a 3-dimensional dye-sensitized solar cell (3D-DSSCs) and module simulating the fractal structure of the pine tree for capturing sunlight. Compared to traditional flat solar cells, this type of solar cell exhibits superiority of absorbing sunlight from all directions. The fabricated 3D-DSSC and module have achieved 3.36% and 3.19% efficiencies, respectively. The results show that the shade has little effect on the performance of 3D-DSSC and module. It is expected that this 3D-DSSC and module have strong potential for practical application due to their 3D light utilization.     

Improved stability quasi-solid-state dye-sensitized solar cell based on polyether framework gel electrolytes

We report three improved stability dye-sensitized TiO₂ photoelectrochemical cells using quasi-solid polymer electrolytes containing poly(propylene oxide) (PPO), poly(ethylene oxide) (PEO) or poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P₁₂₃). After introducing the polyether into the liquid electrolyte, the parameters of these quasi-solid-state solar cells are 90% comparable to that of the liquid photochemical cells, although the conductivities of these polyether framework gel electrolytes are lower than that of the bulk liquid electrolyte. The different morphologies of dried liquid electrolyte and the polyether gel electrolytes are characterized with an atomic force microscope (AFM) to explain the better stability exhibited by the polyether gel electrolytes.     

Application of micro-porous polycarbonate membranes in dye-sensitized solar cells: Cell performance and long-term stability

This research investigates the cell performance and long-term stability of dye-sensitized solar cells (DSSCs) containing micro-porous polycarbonate (PC) film as the frame work material to stabilize the electrolyte solution. The track-etched PC film has cylindrical pore geometry, which is beneficial for ion transport in the electrolyte trapped inside the PC film. The photovoltaic efficiency of the DSSC with 0.2-μm PC membrane is 5.75 ± 0.73% under irradiation of 100 mW cm⁻², which is slightly lower than that (6.34 ± 0.44%) of cells without PC film. The differences in fill factor and open-circuit voltage between the DSSCs with and without PC film are not statistically significant. The long-term cell performance is carried out at continuous illumination of 100 mW cm⁻² (1 sun) and in darkness at 60 °C for up to 1000 h. There is no significant efficiency difference between the cells with and without PC film in light soaking (4.33% vs. 4.52%) for 960 h. In darkness, however, the cells with PC film demonstrate much higher efficiency (at 2.37%) than cells without PC (0.85%) after 1000 h. The improved long-term efficiency data and the higher percentage of working cells confirm the superior lifetime and performance using the micro-porous PC film.     

Assessment of the dye-sensitized solar cell

The field of solar electricity, or photovoltaics (PV), is rich in that there are many materials and concepts for converting sunlight into electricity. The technologies accepted as conventional are those well along in the process of commercialization. The dye-sensitized solar cell, developed in the 1990s, is a nonconventional solar electric technology that has attracted much attention, perhaps a result of its record cell efficiency above 10%. This paper reviews the technology, discusses new research results and approaches presented at a recent symposium of many of the world's important dye solar cell researchers, and presents an assessment of the dye-sensitized solar cell in a comparison with current conventional solar electric technologies. It concludes the dye solar cell has potential for becoming a cost-effective means for producing electricity, capable of competing with available solar electric technologies and, eventually, with today's conventional power technologies. But it is a relatively new technology and faces many hurdles on the path to commercialization. Because of its potential, this assessment recommends further funding for research and development (R&D) of the dye-sensitized solar cell technology on the basis of the promising technical characteristics of the technology, a strong US and worldwide research base, positive industry interest, and today's relatively small funding allocation for its R&D.     

Thermal behaviour assessment of a novel vertical greenery module system: first results of a long-term monitoring campaign in an outdoor test cell

Vertical greenery modular systems (VGMSs) are an increasingly widespread building envelope solution aimed at improving the aesthetical quality of both new and existing façades, contemporarily achieving high energy efficiency performance. Within a research project, a new prototype of VGMS was developed, designed and tested. An experimental monitoring campaign was carried out on a test cell located in Turin (northern Italy), aimed at assessing both biometric parameters and energy-related issues. Two different types of growing media and two plant species, Lonicera nitida L. and Bergenia cordifolia L., have been tested on a south-facing lightweight wall. Results have been compared to the same wall without VGMS and plaster finished, in order to characterise the thermal insulation effectiveness in the winter period and the heat gain reduction in the summer period. Measured equivalent thermal transmittance values of the green modular system showed a 40 % reduction, when compared to the plastered wall, thus noticeably impacting on the energy crossing the façade during the heating season. Benefits of the VGMS are measured also during the summer season, when the presence of vegetation lowers the outdoor surface temperatures of the wall up to 23 °C compared to the plastered finishing, with a positive effect on outdoor comfort and urban heat island mitigation. Nevertheless, as far as the entering energies are concerned, not significant reduction was observed for VGMS, compared to the reference plastered wall, since the green coverage acts as a thermal buffer and solar radiation is stored and slowly released to the indoor environment.     

Analysis and design of dye-sensitized solar cell

This paper presents a methodology to numerically investigate the influence of design and operating parameters on the performance of dye-sensitized solar cell (DSSC). A one-dimensional steady-state model of the DSSC coupled with a model to predict global irradiance on a terrestrial surface is utilized to analyze the performance of a DSSC installation. Hourly, daily, monthly and annual performance of a DSSC installation is systematically analyzed over a wide range of design and operating parameters and the optimum configuration is identified with the objective of maximizing the power density. Overall, this paper illustrates a methodology to ascertain the optimal design and operating configurations of a DSSC which can be extended to any terrain.     

太阳电池组件封装工艺研究

分析了太阳电池组件三种封装工艺的优缺点,并对自行研制的紫外固化胶的装胶黏度及透光率进行了测试,获得了基本适合于透明光伏组件紫外固化封装要求的紫外固化封装胶。     

Degradation mechanisms in a dye-sensitized solar cell studied by UV–VIS and IR spectroscopy

By deliberately causing degradation of components in a dye-sensitized solar cell we have studied failure mechanisms of such cells. The dye, bis(tetrabutylammonium) cis–bis(thiocyanato)bis(2,2^′-bipyridine-4-carboxylic acid, 4^′-carboxylate)ruthenium(II), adsorbed to a nanostructured TiO₂ film was studied with UV–VIS and IR spectroscopy after being exposed to visual and ultra-violet radiation, increased temperature, air, electrolyte, and water in the electrolyte. The thiocyanate ion ligand is lost in air, at temperatures equal to and above 135 °C, in electrolyte and possibly upon UV irradiation. The loss of the SCN⁻ ligand in air was accelerated under visual illumination. From working electrodes immersed in the electrolyte or in degraded complete solar cells it was observed that the absorption peak from the thiocyanate ion ligand at around 2100 cm⁻¹ had broadened, blue-shifted and decreased. One failure mechanism is thus that the thiocyanate ion ligand is lost from the dye together with the electrolyte. Together with water in the electrolyte (5 v%) the SCN⁻ ligand is exchanged with H₂O and/or OH⁻. The ligand exchange between SCN⁻ and H₂O/OH⁻ was accelerated under visual illumination.     

Thermal stability of dye-sensitized solar cells with current collecting grid

Several endurance tests were carried out to investigate thermal stability of a dye-sensitized solar cell (DSC). In the case of applying an ionic liquid-based electrolyte, no obvious leakage of electrolyte components such as iodine was detected on keeping the cell at 85 °C. In addition, double-sealing package was applied to the cell by way of separate cell components from outer moisture. Based on the result, large-sized DSCs with current collecting Ag grid were fabricated, and over 1000 h stability of the cell was accomplished under the heat and humidity environment (85 °C, 85% RH). It was also showed almost no degradation of the performance under the heat and cool cycle stress (?40 and 90 °C) for more than 200 cycles.     

On the modeling of the dye-sensitized solar cell

A simplified electric model of the dye-sensitized electrochemical solar cell (DSC) is presented. It permits the calculation of internal steady-state cell characteristics like particle density distributions or the electric field as a function of the (measured) external current I_ext. The cell is modeled as an one-dimensional pseudo-homogeneous medium of thickness L, where all the electroactive particles involved in the current supporting process move according to different effective transport coefficients (i.e. effective diffusivities D and effective mobilities μ). The electroactive particles are the electrons e⁻ injected into the nanoporous TiO₂ layer after light absorption by the dye, the reduced and the oxidized counterpart of the redox electrolyte El_Red and El_Ox, and the positively charged cation Kat⁺ being brought into the cell together with the electrolyte. By applying the continuity equation, the transport-equation and Poisson's equation to all the electroactive species involved (e⁻, El_Red, El_Ox and Kat⁺) and by assuming a linear Boltzmann relaxation approximation for the back reaction, a system of differential equations is derived, describing particle densities, particle currents and the electric field within the cell. The underlying simplifying assumptions as well as the resulting limits of the model are stated, and some possible extensions are given. This paper aims to outline the general ideas and limitations of the proposed electric modeling, numerical calculations have been successfully implemented, but will be presented in a future paper.     

Phenomenological modeling of dye-sensitized solar cells under transient conditions

A phenomenological model is proposed for a better understanding of the basic working mechanisms of dye-sensitized solar cells (DSCs). A steady-state approach allows the construction of the I-V characteristics, giving important informations about the main factors that influence DSCs’ performance. On the other hand, the transient approach model is an important tool to relate the phenomenological behavior with certain dynamic techniques, such as Electrochemical Impedance Spectroscopy (EIS). Bearing in mind the uncertainty arising from fitting the experimental Nyquist diagrams to general electrical analogues, this transient model contributes for a deeper understanding of the DSCs and for obtaining the relevant kinetic parameters with higher accuracy. The one-dimensional transient phenomenological model presented here assumes that the injected conduction-band electrons may recombine only with the electrolyte redox species. Due to the small dimension of the titania particles, no significant electrical potential gradient is considered, resulting only in a diffusive electron transport across the semiconductor. For modeling purposes, the mesoscopic porous structure, consisting of TiO₂ nanoparticles covered with light-absorbing dye molecules and interpenetrated by the redox mediator (electrolyte), is considered as a homogeneous nanocrystalline structure of thickness L. The continuity and transport governing equations are defined for the mobile species involved: electrons in the TiO₂ conduction band and ions in the electrolyte. The simulated results are in straight agreement with the experimental data.     

Photovoltaic performance of dye-sensitized solar cells stained with black dye under pressurized condition and mechanism for high efficiency

A porous TiO₂ layer was stained with black dye (BD) under a pressurized CO₂ atmosphere. Jsc of the cell (20.66 mA/cm²) was higher than that prepared by a conventional dipping process (18.96 mA/cm²). The higher Jsc was explained by the decrease in surface-state density on the nano-porous TiO₂ layer. In addition, BD aggregation was found to be retarded under the pressurized CO₂ condition, which is also associated with the higher Jsc. These phenomena were explained by the low BD concentration in the CO₂ fluid, the swift reaction rate between TiOH and HOCO dye, and the high diffusion coefficient of BD molecules into porous TiO₂ layers.     

Performance of amorphous silicon solar cell module and solar lantern

The solar lantern (manufactured by BHEL) could regularly be lit for 5–6 h up to a maximum of 7 h, if the battery was fully charged. It is desirable, for regular use, that the solar lantern should be lit for not more than 5 h a day if the clear sky condition exists. If the weather is partially cloudy, use of the lantern should be reduced accordingly. A performance study of the amorphous silicon (a-Si) module shows that the maximum power transfer voltage (V_mp) and corresponding current is ca. 65 and 75% of the open circuit voltage (V_oc) and short circuit current (I_sc), respectively. Efficiency of the module is 3–4% under field conditions and is slightly greater for a higher ambient temperature.     

A concentrator module of spherical Si solar cell

Spherical Si solar cell, which is made up of Si spheres with a diameter of approximately 1.0 mm, is expected to be a promising candidate for low consumption of Si feedstock and simple process technology. This paper describes the formation process and the structure of a concentrator module in detail. The concentrator lens was formed by casting with ultraviolet light hardening resin. The concentration ratio was 4.4 times and the pitch between the spheres was 2.0 mm. By this module design, it was possible to realize a consumption of the Si feedstock of about 3.0 g/W. Conversion efficiencies of 11.3% from single-sphere cell, 8.5% from a 23-spheres module and 5.2% from a 105-spheres module under AM1.5, 100 mW/cm² illumination were achieved.     

Improvement in durability of flexible plastic dye-sensitized solar cell modules

Large-area integrated modules of flexible plastic type dye-sensitized solar cell (DSC) have been fabricated based on polyethylene naphthalate (PEN) film for practical applications such as ubiquitous power sources. From the view point of improving durability, composition of organic solvent-based electrolytes has been investigated. As a result, a plastic DSC module using LiI-free electrolyte maintained its energy conversion efficiency of 2% over 220 h under the accelerated condition of 55 °C and 95% relative humidity.     

Performance variation of carbon counter electrode based dye-sensitized solar cell

The effect of dark and room temperature aging on the performance of carbon counter electrode based dye-sensitized solar cell (DSSC) has been investigated. Using nano size carbon as a counter electrode material, DSSC with power conversion efficiency of 7.56% was fabricated. Storing the devices in the dark at room temperature enhanced both the open-circuit voltage (V_OC) and fill-factor (FF) but reduced the short-circuit current density (J_SC). After 60 days of aging, carbon counter electrode DSSC retains 84% of its initial day efficiency (η). The variation in the current–voltage parameters was explained on the basis of electrochemical impedance spectroscopic (EIS) analysis.