Synthesis and optimization of P(MMA-BA-MAA)/PEG-based polymer gel electrolytes

A polymer gel electrolyte based on poly(methyl methacrylate-butyl acrylate-methacrylic acid)/polyethylene glycol 400 blend (P(MMA-BA-MAA)/PEG400) was successfully prepared by a simple and efficient procedure. The optimal ionic conductivity was achieved to be 3.12 mS cm^?1 at the temperature of 30 °C when the electrolyte has the composition of 20 wt% P(MMA-BA-MAA)/PEG400 blend, 0.6 M NaI, and 0.06 M I₂ in the solvent γ-butyrolactone (GBL). For tuning the ionic conductivity, various additives were introduced into the polymer gel electrolytes. The measured values of open circuit voltage, short circuit current, and total photovoltaic efficiency indicates that the adding of pyridine (PY) leads to better performance of the final dye-sensitized solar cells (DSSCs), while the adding of Guanidine thiocyante (GuSCN) leads to a worse one. 4-Tert-butylpyridine (TBP) additive takes a more complex effect on the performance of the final DSSCs. For polymer gel electrolyte with 0.5 M pyridine, the final fabricated dye-sensitized solar cell has overall energy conversion efficiency (η) of 3.63 % (0.16 cm² active area) under AM 1.5 at irradiation of 100 mW cm^?2, which reached the level of the liquid electrolyte based device (η = 3.83 % at 0.16 cm² active area). Meanwhile, this gel electrolyte exhibits well long-term stability. The mechanism analysis revealed the dependences of ionic conductivity on the concentration of polymer and NaI and the temperatures.     

Novel D-π-A dye sensitizers of polymeric metal complexes with phenylethyl or carbazole derivatives as donors for dye-sensitized solar cells: synthesis,characterization, and photovoltaic application

Four novel polymeric metal complexes containing D-π-A type structures were synthesized, characterized and applied as dye sensitizers in dye-sensitized solar cells (DSSCs). The alkoxy benzene or carbazole (CZ) derivative acts as an electron donor (D), C=C acts as π-bridge (π) and the 8-hydroxyquinoline derivative complex acts as electron acceptor. Bipyridine derivative was ancillary ligand as well as providing anchoring group. FT-IR, gel permeation chromatography, thermogravimetric analyses, differential scanning calorimetry, UV–Vis absorption spectroscopy, Elemental analysis, cyclic voltammetry, J-V curves and input photon to converted current efficiency plots were introduced to investigate the four dyes. These dyes exhibit good thermal stability with 5 % weight loss at temperatures (T_d) of around 300 °C. For the DSSCs devices using dyes with CZ derivatives as electron D (P2, P4) exhibited higher power conversion efficiency (PCE) than that with alkoxy benzene (P1, P3). The DSSC based on P4 exhibited the highest PCE value of 2.42 % (J _sc  = 4.93 mA/cm², V _oc  = 0.73 V, FF = 67.2 %) under AM 1.5G solar irradiation. This indicates a new way to design dye sensitizers for DSSCs.     

Dye-sensitized solar cells based on ZnO nanoflowers and TiO2 nanoparticles composite photoanodes

ZnO nanoflowers were synthesized by low temperature solution-phase method. ZnO nanoflowers/TiO₂ nanoparticles composite photoanodes with various mass ratios were prepared on transparent conductive fluorine-doped tin oxide substrates by doctor-blade technique. The dye-sensitized solar cells (DSSCs) were assembled. The morphology characteristics of ZnO nanoflowers and ZnO/TiO₂ composite photoanodes have been analyzed by scanning electron microscopy. The effect of the ZnO nanoflowers/TiO₂ nanoparticles mass ratio on the performance of DSSCs was systematically investigated by I–V characteristics and electrochemical impedance spectroscopy. Results show that the conversion efficiency of the dye-sensitized solar cell with a ZnO/TiO₂ mass ratio of 25:75 was increased by about 35 % compared to that of pure TiO₂-based solar cell. Addition of ZnO nanoflowers can enhance the light harvesting and improve electron transport.     

Dye-sensitized solar cells based on multilayered ultrafine TiO2 nanowire photoanodes

A low-temperature hydrothermal method was used to synthesize ultrafine TiO₂ nanowires with the diameter of 4–6 nm. The ultrafine nanowires tend to gather together, forming nanowire bundles. The length of the nanowires is about 1–4 μm, depending on the growth time. Multilayered TiO₂ nanowires with the height more than 10 μm have been synthesized by a multi-step growth process. Furthermore, the dye-sensitized solar cells (DSSCs) are assembled using single-layered, double-layered and triple-layered TiO₂ nanowires as photoanode respectively. The DSSC based on triple-layered TiO₂ nanowires shows the highest power conversion efficiency of 3.96 % among the prepared samples. The relatively high energy conversion efficiency is attributed to the large surface area, which enhances the absorption of dye molecules.     

ZnO nanosheet-based hierarchical microarchitectures for enhanced conversion efficiency in dye-sensitized solar cells

Hierarchical ZnO microarchitectures have been fabricated on a large scale by a simple and economical citrate-mediated hydrothermal route for application in dye-sensitized solar cells (DSSCs). These flowerlike architectures are constructed by many interleaving nanosheets which have ultrathin thickness of about 5 nm. Compared with the DSSCs based on other forms of nanostructures, such as ZnO nanorods and nanoparticles, the DSSCs constructed by these hierarchical ZnO microarchitectures demonstrate a remarkable enhancement in photoelectric conversion efficiency. This enhanced performance is mainly due to the large surface area of the hierarchical microarchitectures for dye loading, and their special structural feature to ensure rapid transportation of electrons. Our results suggest that this new type of ZnO nanosheet-based microarchitectures is a promising material for application in DSSCs.     

Fabrication and characterizations of PCDTBT: PC71BM bulk heterojunction solar cell using air brush coating method

Organic solar cells have been significantly attracted due to the need to develop an inexpensive clean and sustainable renewable energy source. We report on the fabrication of poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]/[6, 6]-phenyl-C₇₁-butyric acid methyl ester blend active layer using airbrush spray-coating method in mixed solvents. Optical absorption of the active layers was analyzed using UV–visible spectral studies in the wavelength range from 300 to 800 nm. The surface morphology of the active layers deposited with different parameters (spraying time and substrate-nozzle distance) was examined using atomic force microscopy. The current density–voltage (J–V) characteristics of photovoltaic cells were measured under the illumination of simulated solar light with 100 mW cm^?2 (AM 1.5G) by an Oriel 1000 W solar simulator. The power conversion efficiency of the solar cell is more than 5 %.     

Influence of secondary anodization voltage on free-standing crystallized TiO2 nanotube array membrane

Vertically aligned, free-standing crystallized TiO₂ nanotube arrays with a length of 32 μm have been fabricated by a two-step anodization method. The TiO₂ nanotube membrane can be detached from the Ti substrate through the secondary anodization process. The influence of the secondary anodization voltage on the morphology, crystalline phase and photovoltaic performance of the as-fabricated samples has been investigated. Results show that the side wall of TiO₂ nanotubes becomes obviously thin as the secondary anodization voltage increases and leads to crack when the voltage reaches 25 V. The mass fraction of the anatase reduces by the increase of the voltage. Furthermore, the dye-sensitized solar cells (DSSCs) based on TiO₂ nanotube arrays have been assembled. The energy conversion efficiency decreases with the increase of secondary anodization voltage, and a highest energy conversion efficiency of 10.6 % under UV illumination (368.1 nm) is obtained from the cell with TiO₂ nanotube membrane re-anodizad at 15 V.     

Expanding the spectral response of a dye-sensitized solar cell by applying a selective positioning method

We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO(2) layer through selective desorption and adsorption processes. From the selective removal of the only upper part of the first adsorbed dye, double-layered dye-sensitized solar cells have been successfully achieved without any damage to the dye. From the incident photon-to-current conversion efficiency (IPCE) measurement, the multi-layered dye-sensitized solar cell (MDSSC) was found to exhibit an expanded spectral response for the solar spectrum while maintaining the maximum IPCE value of each single-layered cell. The highest photocurrent density, 19.3 mA cm( - 2), was obtained from the MDSSC utilizing an N719/N749 bi-layered mesoporous TiO(2) film. The power conversion efficiency of 9.8% was achieved from the MDSSC, which is higher than that of single N719-or N749-based cells and cocktail-dyed (a mixture of N719 and N749) cells.     

Enhancing the performance of dye-sensitized solar cells by ZnO nanorods/ZnO nanoparticles composite photoanode

In this paper, ZnO nanorods (NRs) were prepared by a two-step solution phase reaction. A composite photoanode architecture is fabricated by adding 0–0.20 at.% ZnO NRs into ZnO nanoparticles (NPs). The scanning electron microscopy image shows that the average diameter and length of the ZnO NRs are about 50 nm and 2–5 µm, respectively, and the ZnO NRs are uniformly embedded into the ZnO NPs photoanode. The UV–vis spectrum analysis reveals that the amount of dye adsorption of the composite photoanode decreases with increasing ZnO NRs content. Meanwhile, the influence of ZnO NRs contents on the dye-sensitized solar cells (DSSCs) performance is systematically investigated. The photocurrent density–voltage (J–V) characteristics reveal that the device performance of DSSCs can be significantly enhanced by the composite photoanode. Typically, the DSSC with 0.15 at.% ZnO NRs obtains the optimal energy conversion efficiency of 3.8%, which is 28.4% higher than that of the pristine ZnO DSSCs. The electrochemical impedance spectroscopy (EIS) analysis shows that ZnO NRs can provide a direct pathway for accelerating electron transport, extending the electron lifetime, suppressing electron recombination and improving electron collection efficiency. These results indicate that the incorporation of ZnO NRs in the photoanode is an effective way to improve the performance of DSSCs.     

Novel in situ crosslinked polymer electrolyte for solid-state dye-sensitized solar cells

A novel poly(citric acid-ethylene glycol)/LiI/I₂ (PCE/LiI/I₂) solid polymer electrolyte (SPE) based on the biodegradable PCE matrix has been prepared in situ, by penetrating of the PCE prepolymer sol into mesoporous TiO₂ photoanode, followed by curing. The PCE prepolymer can easily penetrate into the mesoporous photoanode, which could induce good interfacial contact between the SPE and photoanode. Assembled with the SPE, highly efficient and stable solid-state dye-sensitized solar cells (DSSCs) have been gained due to the good interfacial contact of SPE/TiO₂ photoanode as well as the favorable ionic conductivity of the SPE. The results show that the contents of CA determine the aggregation structure such as the inter-segmental distance and free volume of the PCE matrix, which consequently affects the ionic diffusion coefficient and conductivity of the PCE/LiI/I₂ electrolyte, and accordingly the photoelectric performance of the DSSCs. With CA content of 32.4 wt%, the SPE reaches the optimal ionic conductivity of 5.43 × 10^?5 S cm^?1 and the solid-state DSSCs obtain the best overall photoelectric conversion efficiency of 1.22 % at 60 mW cm^?2.     

Influence of growth time and annealing on rutile TiO2 single-crystal nanorod arrays synthesized by hydrothermal method in dye-sensitized solar cells

Vertically aligned TiO₂ nanorod (NR) arrays have been grown on the fluorine doped tin oxide (FTO) substrates by hydrothermal methods and the structures were employed to fabricate the dye-sensitized solar cells (DSSCs). The charge transport properties were investigated by the current to voltage curves and the electrochemical impedance spectroscopy. It was found that DSSCs containing the as-prepared and 500 °C annealed TiO₂ NRs exhibit different trends with the growth time (t). The DSSCs assembled with the un-sintered NR arrays showed the highest power conversion efficiency (η) of 1.87%. When DSSCs were assembled with the sintered NR arrays, nearly 400% enhanced efficiency were obtained, and the values (η) showed a positive correlation with t. This behavior may be attributed to the improved adhesion and electric contact between TiO₂ and FTO, as well as the reduced number of recombination sites.     

Electrospun TiO2-MWCNTs nanofibers as photoanode in dye-sensitized solar cell (DSSC)

Electrospinning process was used to fabricate hybrid TiO₂ nanofibrous membrane containing multi-walled carbon nanotubes (MWCNTs). The MWCNTs treated with plasma modification as established in our previous studies are dispersed in the mixture of titanium (IV) isopropoxide and poly(methyl methacrylate) in N,N-dimethylformamide prior to electrospinning. Diameter of the calcined TiO₂-MWCNTs nanofibers (NFs) ranged from 100 to 200 nm, and transmission electron microscopy shows that the MWCNTs are both embedded and lying externally on the NFs. Photoanodes for dye-sensitized solar cells are prepared by first conglutinating the nanofibrous membranes onto conducting glass substrate under methanol vapor treatment followed by calcination and dye sensitization. The NFs exhibit improved conducting behavior (from 10^?8 to 10^?6 S/m) with small quantity (0.5–1.5 wt%) of MWCNTs. An optimum addition of 1.0 wt% MWCNTs into the TiO₂ nanofibrous membrane improves the overall solar conversion efficiency by 47 % with significant increase in the short-circuit photocurrent. Electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy analyses reveal that the enhanced electron transport with smaller resistance is responsible for the improved cell performance. The results suggest that the conducting properties of the MWCNTs are crucial for faster transport of photogenerated electrons, hence retarding charge recombination that could result in poor conversion efficiency.     

Intertwined aligned carbon nanotube fiber based dye-sensitized solar cells

Metal wires suffer from corrosion in fiber-shaped dye-sensitized solar cells (DSSCs). We report herein that stable, ultrastrong, and highly flexible aligned carbon nanotube fibers can be used not only as catalytic counter electrodes but also as conductive materials to support dye-loaded TiO(2) nanoparticles in DSSCs. The power conversion efficiency of this fiber solar cell can achieve 2.94%. These solar power fibers, exhibiting power conversion efficiency independent of incident light angle and cell length, can be woven into textiles via a convenient weaving technology.     

Copper oxide thin film and nanowire as a barrier in ZnO dye-sensitized solar cells

The ZnO dye-sensitized solar cells (DSSCs) with different photoelectrodes were studied on the effect of CuO layer as a barrier layer toward power conversion characteristics. The structures of DSSCs based on ZnO as a photoelectrode, Eosin-Y as a dye sensitizer, iodine/iodide solution as an electrolyte and Pt/FTO as a counterelectrode. CuO powder, nanowire prepared by oxidation reaction of copper powder and CuO thin film prepared by evaporation copper thin film, were used as a layer on the top of ZnO layer to form blocking layer. The photocurrent, photovoltage and power conversion efficiency characteristics for DSSCs were measured under illumination of simulated sunlight obtained from a solar simulator with the radiant power of 100 mW/cm². It was found that ZnO DSSCs with CuO thin film exhibited highest current density of 5.10 mA/cm² and highest power conversion efficiency of 0.92% than those of CuO powder and nanowire. The enhancement of the power conversion efficiency can be explained in terms of the retardation of the interfacial recombination dynamics of CuO blocking layer.     

Performance improvement of dye-sensitized solar cells by surface patterning of fluorine-doped tin oxide transparent electrodes

The surface modification of fluorine-doped tin oxide (FTO) transparent electrodes was carried out by lithography and inductively coupled plasma etching to improve the conversion efficiency of dye-sensitized solar cells (DSSCs). The concentration of Cl₂ gas and dc-bias voltage to the substrate were varied as the main etch parameters. The transmittance and sheet resistance of the FTO electrodes were compared before and after etching. The DSSCs fabricated on the patterned FTO electrodes showed higher conversion efficiency than those fabricated on the ordinary FTO electrodes without patterns. Scanning electron microscopy showed that more TiO₂ particles could be involved in the DSSCs with patterned FTO electrodes, and that the contact between the TiO₂ layer and electrode were improved by patterning the FTO electrode. The current-voltage curves and incident photon to current efficiency spectra showed that a significantly higher photocurrent was produced in the DSSCs fabricated on the patterned FTO.     

Performance Maintenance of Dye-Sensitized Solar Cells Using a Latent Heat Storage Material

Recently, there has been considerable interest in various renewable energies. Among them, solar cell production has increased markedly because the photovoltaic is a clean and safe power generation method. The dye-sensitized solar cell (DSSC) has attracted much attention as an alternative to silicon solar cells due to lower manufacturing costs and plentiful resources for DSSC production. However, the performance of DSSCs has been limited by their durability and low photoelectric conversion efficiency. Temperature control of DSSCs via phase-change materials (PCMs) is expected to improve performance. In this study, DSSCs were heated or cooled with a heat exchanger copper block that was in contact with a PCM (heptadecane), while being irradiated by a solar simulator light source. The durability and photoelectric conversion efficiency of the DSSC improved under PCM temperature control.     

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.     

Preparation of Zr-doped mesoporous TiO2 particles and their applications in the novel working electrode of a dye-sensitized solar cell

This paper presents an implementation of our recent theory on the suspension of electron-hole recombination via electronic- and micro-structure optimization to study the influence of Zr-doping on the efficiency (η) of TiO₂-based dye-sensitized solar cells (DSSCs). We developed a four-layered working electrode, in which the size of particles increased from the bottom layer of TiO₂ (P-25) through three successive layers of Zr-doped TiO₂, which were calcined at 450, 600, and 850 °C respectively. The enhancement in open-circuit photovoltage (V_oc) and short-circuit photocurrent density (J_sc) can be attributed to the electronic- and micro-structures in the working electrode. The former is related to band bending, whereas the latter is related to light-scattering within multiple layers. Simulation results (FactSage) demonstrate that Zr doping in TiO₂ can suspend or delay the formation of oxygen vacancies and thereby reduce the number of electron scattering centers, which helps to suspend electron-hole recombination by strengthening Ti-O bonds. The proposed four-layered working electrode produced an 80.2% increase in η, compared with DSSCs using a TiO₂ (P-25) electrode. This study demonstrated a novel metal doping strategy for the manipulation of electronic structure and photoelectron conversion efficiency. The proposed methodology could also be used to guide the design of photo-catalysts in general.     

Dye-sensitized solar cells based on composite TiO<Subscript>2</Subscript> nanoparticle–nanorod single and bi-layer photoelectrodes

TiO₂ nanoparticle (NP), composite TiO₂ nanoparticle–nanorod (NP–NR) and bi-layer TiO₂ nanoparticle/nanorod (NP/NR) with the optimized diameter of NRs had been prepared as anode layer in dye-sensitized solar cells (DSSCs). Morphology and thickness of anode layers were provided by field emission scanning electron microscope (FE-SEM) and scanning electron microscopy (SEM) devices. Current density–voltage diagrams were prepared by potentiostat and solar simulator devices at air mass (AM) 1.5. It is determined that DSSCs based on composite NP–NR photoelectrode had the best conversion efficiency of 5.07%. Also, the results of the electrochemical modelling of these DSSCs indicated that solar cells based on NP–NR electrode had the highest electron transport time (τ _d) of 312.87 ms, electrons’ recombination lifetime (τ _n) of 130.4 ms and the lowest transfer resistance (R _ct) as well as transport resistance (R _t) of 22.46 and 9.4 Ω, respectively.     

Synthesis of hierarchical nanoparticles-based ZnO spheres for their application as the light blocking layers in dye-sensitized solar cells

Three-dimensional nanoparticles-based ZnO hierarchical spheres (ZnO-HS) with strong light harvesting and dye loading abilities have been fabricated by a simple hydrothermal method in this paper. These ZnO-HS were designed as the overlayer for light blocking and applied to the dye-sensitized solar cells (DSSCs) based on bare ZnO nanoparticles (ZnO-NP) or TiO₂ nanoparticles (TiO₂-NP). The results show that the values of the short-circuit current density (J _sc) and the power conversion efficiency (η) have been heightened up to 12.6 mA cm^?2 and 3.40 % for the ZnO-NP/ZnO-HS double-layered DSSC, far higher than the bare ZnO-NP DSSC. However, another DSSC assembled by the TiO₂-NP/ZnO-HS double-layered film displays an adverse result for the decreasing of J _sc and η even though the ZnO-HS light blocking layer has been established on the TiO₂-NP film. According to the electrochemical impedance data compared between the ZnO-NP/ZnO-HS double-layered and TiO₂-NP/ZnO-HS double-layered DSSC, it is found that the former possesses less possibility for the occurrence of charge recombination and electronic loss, which is responsible for its better photovoltaic response.