Energy Conversion Efficiency Of Dye-sensitized Solar Cells Research Articles

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.

Effect of TiO2Coating Thickness on Photovoltaic Performance of Dye-sensitized Solar Cells Prepared by Screen-printing Using TiO2Powders

Dye-sensitized solar cells (DSSCs) were synthesized using a 0.25 cm 2 area of a TiO 2 nanoparticle layer as the electrode and platinum (Pt) as the counter electrode. The TiO 2 nanoparticle layers (12 to 22 μm) were screen-printed on fluorine-doped tin oxide glass. Glancing angle X-ray diffraction results indicated that the TiO 2 layer is composed of pure anatase with no traces of rutile TiO 2 . The Pt counter electrode and the ruthenium dye anchored TiO 2 electrode were then assembled. The best photovoltaic performance of DSSC, which consists of a 18 μm thick TiO 2 nanoparticle layer, was observed at a short circuit current density (Jsc) of 14.68 mA·cm -2 , an open circuit voltage (V oc ) of 0.72V, a fill factor (FF) of 63.0%, and an energy conversion efficiency (η) of 6.65%. It can be concluded that the electrode thickness is attributed to the energy conversion efficiency of DSSCs.

High temperature processed ZnO nanorods using flexible and transparent mica substrates for dye-sensitized solar cells and piezoelectric nanogenerators

The authors report the synthesis of ZnO nanorods on flexible and transparent mica substrates. The coupled use of polyethylenimine and ammonium hydroxide provided a direct method for growing vertically well-aligned ZnO nanorods with a high aspect ratio. Using mica as a substrate material enabled thermal annealing processes, which improved the structural and optical properties of ZnO nanorods with uniform surface coverage and excellent adhesion, increased transmittance of indium tin oxide (ITO)/mica (52%), and decreased sheet resistance of ITO/mica (80%). We have fabricated ZnO nanorod-based dye-sensitized solar cells (DSSCs) and piezoelectric nanogenerators (NGs) and investigated their annealing effects on the device performances. Specifically, the thermal treatment at 500°C for 30min increased the energy conversion efficiencies of DSSCs by 53%. Furthermore, we observed a three-fold increase in the NG׳s output voltage and output current density through this thermal annealing process. As shown below, mica, which can function under extremes of temperature, is useful as a substrate for flexible and transparent electronics.

Photovoltaic properties of TiO2–ZrO2 fiber composite electrodes for dye-sensitized solar cells

ZrO2 fibers were fabricated by sol–gel and electrospinning techniques for use in dye-sensitized solar cells (DSCs). The addition of ZrO2 fibers into TiO2 electrodes provides good dye loading and an effective electron pathway to increase the charge transfer in the TiO2/electrolyte interface over conventional TiO2 electrode. Photo-electrochemical properties of TiO2–ZrO2 fiber composite electrodes and the performance of resultant DSCs were determined from their photovoltaic-current densities. Energy conversion efficiency of DSCs with a TiO2–ZrO2-700 composite electrode was 6.2%, an increase of 26.5% than pure TiO2 electrode of 4.9%. The electron recombination times of the pure TiO2 and TiO2–ZrO2-700 electrode were 15.94 and 21.69ms, respectively.

Quinoline and Fluorene- Functionalized Porphyrins for Nanocrystalline Solar Cells

Dye-sensitized solar cell (DSC) is an electrochemical device that has two electrodes with electrolyte between them. Recently the energy conversion efficiency of DSCs using a zinc porphyrin as a sensitizer has reached >12%. However, most porphyrin dyes exhibit narrow absorption in the visible region and relatively weak absorption in the red and near-infrared region; as a result, photons in these regions are not sufficiently converted to electrons, which has been a bottle-neck for high efficiency solar cells. Additionally, the widely used benzoic acid for attaching porphyrin dyes to titanium dioxide nanoparticles tends to dissociate into electrolyte, leading to poor long-term stability. In this presentation, synthesis, characterization, photophysical properties, electrochemical and photovoltaic properties of several novel porphyrin dyes with enhanced binding strength and broader light absorption capability will be discussed. We found that 8-hydroxylquinoline-functionalized porphyrin exhibited stronger binding capacity on the titanium dioxide nanoparticle surface, broader and stronger absorption in the red region compared to conventional benzoic acid-functionalized porphyrins. We will also discuss the porphyrins that are functionalized by alkyl fluorene groups. The results demonstrate the potential of these dyes for achieving high efficiency in DSCs.

The effect of light-scattering layer on the performance of dye-sensitized solar cell assembled using TiO2 double-layered films as photoanodes

Dye-sensitized solar cells (DSSCs) are fabricated based on double-layered films of TiO2 nanospheres and TiO2 nanorod arrays (NRAs). TiO2 nanospheres, including TiO2 hollow spheres (HSs) and TiO2 solid spheres (SSs), were served as light-scattering layers on TiO2 NRAs as composite photoanodes. The as-prepared TiO2 NRAs, TiO2 HSs and TiO2 SSs have been characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photoelectric properties of DSSCs were investigated by UV–vis reflectance spectra, current–voltage curves and electrochemical impedance spectroscopy. Owing to the synergic effects of the TiO2 HSs (SSs) and NRAs, including large specific surface area of HSs (SSs) as light-scattering layer for effective dye adsorption and harvesting light and rapid electron transport in one dimensional TiO2 NRAs, the optimal energy conversion efficiency of DSSCs with as-prepared double-layered films as nanocomposite photoanode (5.40%) were far higher than the ones using single-layered NRAs films (1.56%).

Enhanced photovoltaic characterization and charge transport of TIO2 nanoparticles/nanotubes composite photoanode based on indigo carmine dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have established themselves as an alternative to conventional solar cells owing to their remarkably high power conversion efficiency, longtime stability and low-cost production. DSSCs composed of a dyed oxide semiconductor photoanode, a redox electrolyte and a counter electrode. In these devices, conversion efficiency is achieved by ultra-fast injection of an electron from a photo excited dye into the conduction band of metal oxide followed by subsequent dye regeneration and holes transportation to the counter electrode. The energy conversion efficiency of DSSC is to be dependent on the morphology and structure of the dye adsorbed metal oxide photoanode. Worldwide considerable efforts of DSSCs have been invested in morphology control of photoanode film, synthesis of stable optical sensitizers and improved ionic conductivity electrolytes. In the present investigation, a new composite nano structured photoanodes were prepared using TiO2 nano tubes (TNTs) with TiO2 nano particles (TNPs). TNPs were synthesized by sol–gel method and TNTs were prepared through an alkali hydrothermal transformation. Working photoanodes were prepared using five pastes of TNTs concentrations of 0, 10, 50, 90, and 100 % with TNPs. The DSSCs were fabricated using Indigo carmine dye as photo sensitizer and PMII (1-propyl-3-methylimmidazolium iodide) ionic liquid as electrolyte. The counter electrode was prepared using Copper sulfide. The structure and morphology of TNPs and TNTs were characterized by X-ray diffraction and electron microscopes (TEM and SEM). The photocurrent efficiency is measured using a solar simulator (100 mW/cm2). The prepared composite TNTs/TNPs photoanode could significantly improve the efficiency of dye-sensitized solar cells owing to its synergic effects, i.e. effective dye adsorption mainly originated from TiO2 nanoparticles and rapid electron transport in one-dimensional TiO2 nanotubes. The results of the present investigation suggested that the DSSC based on 10 % TNTs/TNPs showed better photovoltaic performance than cell made pure TiO2 nanoparticles. The highest energy-conversion efficiency of 2.80 % is achieved by composite TNTs (10 %)/TNPs film, which is 68 % higher than that pure TNPs film and far larger than that formed by bare TNTs film (94 %). The charge transport and charge recombination behaviors of DSSCs were investigated by electrochemical impedance spectra and the results showed that composite TNTs/TNPs film-based cell possessed the lowest transfer resistances and the longest electron lifetime. Hence, it could be concluded that the composite TNTs/TNPs photoanodes facilitate the charge transport and enhancing the efficiencies of DSSCs.

ZnO hierarchical aggregates: Solvothermal synthesis and application in dye-sensitized solar cells

ZnO hierarchical aggregates have been successfully synthesized by solvothermal methods through reaction of zinc acetate and potassium hydroxide in methanol solution. The shapes of the aggregates were controlled by varying the ratio of Zn2+ and OH− ions in the reaction system, while the size can be tuned from 2 μm to 100 nm. Oriented attachment was found to be the main mechanism of the three-dimensional assembly of small ZnO nanocrystallites into large aggregates. The performance of these aggregates in dye-sensitized solar cells (DSCs) indicated that hierarchical structured photoelectrodes can increase energy conversion efficiency of DSCs effectively when the sizes of aggregates match the wavelengths of visible light. Open image in new window

Hybrid electrolytes prepared from ionic liquid-grafted alumina for high-efficiency quasi-solid-state dye-sensitized solar cells

Alumina (Al2O3) nanoparticles were covalently surface-modified with an ionic liquid (IL) to improve their miscibility with ILs such as 1-methyl-3-propylimidazolium iodide (MPII). Hybrids consisting of MPII and the surface-modified IL-Al2O3 nanoparticles were utilized as an I2-free electrolyte for quasi-solid-state dye-sensitized solar cells (DSSCs). The synthesis and properties of the IL-Al2O3 nanoparticles and hybrid electrolytes were characterized by Fourier transform infrared (FT-IR) spectroscopy, UV-visible spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The viscosity of the electrolyte continuously increased with the content of IL-Al2O3, and the fluidity almost disappeared completely when the MPII:IL-Al2O3 weight ratio was 95 : 5 or 90 : 10. The energy conversion efficiencies of DSSCs fabricated with IL-Al2O3 were always greater than those with pristine Al2O3. Such a finding is due to the favorable interactions and good miscibility between MPII and IL-Al2O3, which in turn results in the formation of an interconnected channel pathway for ion transport. Incident photon-to-electron conversion efficiency (IPCE), intensity modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS) measurements were used to investigate the interfacial properties and electron transport characteristics. Upon utilizing double-layer structures with mesoporous TiO2 beads, the efficiency increased to 7.6% at 100 mW cm(-2), one of the highest values reported for quasi-solid-state DSSCs.

Highly efficient dye-sensitized solar cells: progress and future challenges

High energy conversion efficiency is one of the most important keys to the commercialization of dye-sensitized solar cells (DSCs) in the huge electricity generation market. According to our experience in the persistent efforts that helped to achieve high efficiency DSCs, we selectively review the major progress of improving the energy conversion efficiency of DSCs which may be useful for future applications. We start the discussion from modelling the device by macroscopic equivalent circuit and then highlight some approaches to improve the device performance, such as the molecular engineering of novel dye sensitizers and light trapping effect, tuning the potential of redox shuttles and surface passivation of photoelectrodes, and optimizing the resistance. Finally, we illustrate a roadmap of possible future directions of DSCs with the challenges of how to further improve the efficiency to accelerate the progress in the commercialization of DSCs.

Improved photovoltaic performance of dye-sensitized solar cells with modified self-assembling highly ordered mesoporous TiO2 photoanodes

Strategies for improving the photovoltaic performance of dye-sensitized solar cells (DSSCs) are proposed by modifying highly transparent and highly ordered multilayer mesoporous TiO2 photoanodes through nitrogen-doping and top-coating with a light-scattering layer. The mesoporous TiO2 photoanodes were fabricated by an evaporation-induced self-assembly method. In regard to the modification methods, the light-scattering layer as a top-coating was proved to be superior to nitrogen-doping in enhancing not only the power conversion efficiency but also the fill factor of DSSCs. The optimized bifunctional photoanode consisted of a 30-layer mesoporous TiO2 thin film (4.15 μm) and a Degussa P25 light-scattering top-layer (4 μm), which gives rise to a ∼200% higher cell efficiency than for unmodified cells and a fill factor of 0.72. These advantages are attributed to its higher dye adsorption, better light scattering, and faster photon–electron transport. Such a photoanode configuration provides an efficient way to enhance the energy conversion efficiency of DSSCs.

Preparation and Characterization of Nano‐Polyaniline Film on ITO Conductive Glass by Electrochemical Polymerization

Polyaniline (PANI) films were synthesized on a conducting ITO glass by potentiostatic techniques to construct a low‐cost counter electrode for dye‐sensitized solar cell (DSSC). The compact layer, nanoparticles, nanorods‐ and fibrils were observed on the top of PANI films with different constant potentials by SEM. Then the conductivity test illuminated that a polyaniline film with the highest conductivity was electrodeposited at 1.0 V. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the potential decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the high surface area, high conductivity, and excellent catalytic activity of PANI electrode. Therefore, the PANI counter electrode with excellent catalytic performance is a potential substitute for platinized electrode to save cost of DSSC.

Dye regeneration and charge recombination in dye-sensitized solar cells with ferrocene derivatives as redox mediators

Ferrocene compounds are promising redox shuttles for application in dye-sensitized solar cells (DSCs). Chemical modification of the cyclopentadienyl rings is easily achievable affording almost unlimited variation of the redox properties. This allows fine-tuning of the driving force for dye-regeneration and optimization of the energy conversion efficiency of DSCs. Herein, six ferrocene derivatives have been chosen for investigation which cover the large redox potential range of 0.85 V, by virtue of simple alkylation and halogenation of the cyclopentadienyl ring, and enable improved matching of the energy levels of the sensitizer and the electrolyte. Although the focus of this work was to examine the effect of the redox potential on charge transfer processes, DSCs were fabricated which achieved high energy conversion efficiencies of over 5%. Charge transfer reactions were studied to reveal the dependence of the dye regeneration rate, recombination losses and recombination pathways on the reaction driving force. An increase in redox potential led to a higher efficiency due to higher open circuit potentials until a threshold is reached. At this threshold, the driving force for dye regeneration (18 kJ mol−1, ΔE = 0.19 V) becomes too small for efficient device operation, leading to rapid recombination between the oxidized dye and electrons in the TiO2 conduction band. As a result of this work guidelines can be formulated to aid the selection of redox couples for a particular sensitizer in order to maximize the utilization of incident solar energy.

Comparison of D-SS and D-ST Dyes as Photo Sensitizers in Dye-Sensitized Solar Cells

为了揭示D-SS和D-ST分子敏化的染料敏化太阳能电池（DSSCs）的物理机制,采用密度泛函理论（DFT）、含时密度泛函理论（TDDFT）和自然键轨道（NBO）分析,模拟计算染料D-SS和D-ST分子的结构、紫外-可见吸收光谱和能级结构.D-SS的紫外-可见吸收光谱相比于D-ST的有明显的红移,而且D-SS分子的摩尔吸光系数也高于D-ST分子的.D-SS分子本应该比D-ST分子拥有更高的俘获太阳辐射光子的能力,但由于D-SS分子的最高占据分子轨道（HOMO）能级位置比氧化还原电解质（I-/I-3）的氧化还原能级高,处于光激发态的D-SS分子向TiO2电极注入电子而被氧化后,不能顺利地从电解质中得到电子而还原,使得D-SS分子俘获光子的能力不能充分发挥,从而严重地降低了由其敏化的DSSCs的光电性能和光电能量转换效率.揭示了D-SS敏化的DSSCs的光电性能,特别是光电能量转换效率比D-ST敏化的DSSCs的低的原因.染料敏化剂分子的HOMO能级的位置对于DSSCs来说也是很重要的,用于DSSCs的有机敏化剂分子的HOMO能级的位置必须低于氧化还原电解质的氧化还原能级.

Effect of Li-doped TiO<SUB>2</SUB> Compact Layers for Dye Sensitized Solar Cells

Both TiO2 compact layer (d-TiO2) and Li-doped TiO2 compact layer (d-Li-TiO2) were deposited between nano-TiO2 and transparent conductive oxide (TCO) for dye sensitized solar cells (DSSC) by the technique of pulsed laser deposition (PLD). XRD pattern shows the compact layers are crystallized in anatase structure. Compared with FTO-based DSSC without compact layer, the open voltage decay measurement shows the novel structure can slow the decay of the open circuit voltage, indicating an effective suppression of back electrons transfer from TCO to the electrolyte by the dense buffer layers. In addition, the interface resistance between the nano-TiO2 and the TCO falls down due to the reduced energy band-gap of Li-doped TiO2, which makes it easier to transfer the generated elec- trons from conducting band of nano-TiO2 to TCO surface, leading an enlarged short current from 4.2 mA/cm 2 of FTO-based to 4.8 mA/cm 2 for that with d-TiO2 and 6.1 mA/cm 2 for d-Li-TiO2, respectively. Thus, the photo- voltaic energy conversion efficiency of DSSC based on the Li-doped TiO2 compact layer enhances as much as 42%

Effect of the TiO2Nanotubes in the Photoelectrode on Efficiency of Dye-sensitized Solar Cell

The effect of nanotube (TNT) and nanoparticle (TNP) composite photoelectrode and the role of TNT to enhance the photo conversion efficiency in dye-sensitized solar cell (DSSC) have investigated in this study. Results demonstrated that the increase of the TNT content (1-15 %) into the electron collecting TNP film increases the open-circuit potential () and short circuit current density (). Based on the impedance analysis, the increased was attributed to the suppressed recombination between electrode and electrolyte or dye. Photochemical analysis revealed that the increased Jsc with the increased TNT content was due to the scattering effect and the reduced electron diffusion path of TNT. The highest (12.6 mA/), Voc (711 mV) and conversion efficiency (5.9%) were obtained in the composite photoelectrode with 15% TNT. However, and was decreased for the case of 20% TNT, which results from the significant reduction of adsorbed dye amount and the poor attachment of the film on the fluorine-doped tin oxide (FTO). Therefore, application of this composite photoelectrode is expected to be a promising approach to improve the energy conversion efficiency of DSSC.

Surface‐Plasmon Assisted Energy Conversion in Dye‐Sensitized Solar Cells

AbstractIn this study, the effect of plasmonic core‐shell structures, consisting of dielectric cores and metallic nanoshells, on energy conversion in dye‐sensitized solar cells (DSSCs) is investigated. The structure of the core‐shell particles is controlled to couple with visible light so that the visible component of the solar spectrum is amplified near the core‐shell particles. In core‐shell particle – TiO2 nanoparticle films, the local field intensity and light pathways are increased due to the surface plasmons and light scattering. This, in turn, enlarges the optical cross‐section of dye sensitizers coated onto the mixed films. When 22 vol% of core‐shell particles are added to a 5 μm thick TiO2 film, the energy conversion efficiency of DSSCs increases from 2.7% to 4.0%, in spite of a more than 20% decrease in the amount of dyes adsorbed on the composite films. The correlation between core‐shell particle content and energy conversion efficiency in DSSCs is explained by the balance among near‐field effects, light scattering efficiency, and surface area in the composite films.

Performance of Dye‐Sensitized Solar Cells Based on MWCNT/TiO2–xNx Nanocomposite Electrodes

AbstractMultiwall carbon nanotube (MWCNT) fibrils were introduced into TiO2–xNx photoelectrodes to enhance charge collection efficiency as charge‐transport pathways. For comparison, we also synthesized MWCNT/TiO2 nanocomposites to fabricate dye‐sensitized solar cells (DSCs). The effect of MWCNTs on the photovoltaic performance of the DSCs was studied in detail. The performance of DSCs based on MWCNT/TiO2–xNx differs significantly from that of MWCNT/TiO2 photoelectrodes. A high energy conversion efficiency of 7.66 % was achieved in the dye‐sensitized MWCNT/TiO2 nanocomposites solar cells. The results show that remarkable enhancement of ca. 33 % and ca. 40 % in the conversion efficiency (η) and short‐circuit photocurrent density (Jsc), respectively, occurrs for the DSCs based on MWCNT/TiO2 than those made of pure TiO2 electrodes. The energy conversion efficiency of DSCs based on TiO2–xNx electrodes was 6.98 %, which is similar to that of MWCNT/TiO2–xNx DSCs (6.88 %–5.17 %). We also investigated the charge collection efficiency, electron transport, electron lifetime, and photocurrent transient behavior by electrochemical analysis. The introduced MWCNTs exhibit a smaller sheet resistance and electron transfer resistance, as well as a longer electron lifetime. A 20 % enhancement in the charge collection efficiency is achieved in the nanocomposite DSCs.

Efficiency improvement of dye-sensitized solar cells using graft copolymer-templated mesoporous TiO2films as an interfacial layer

Organized mesoporous TiO2 films with high porosity and good connectivity were synthesized via sol–gel by templating an amphiphilic graft copolymer consisting of poly(vinyl chloride) backbone and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM. The randomly microphase-separated graft copolymer was self-reorganized to exhibit a well-ordered micellar morphology upon controlling polymer–solvent interactions, as confirmed by atomic force microscope (AFM) and glazing incidence small-angle X-ray scattering (GISAXS). These organized mesoporous TiO2 films, 550 nm in thickness, were used an an interfacial layer between a nanocrystalline TiO2 thick layer and a conducting glass in dye-sensitized solar cells (DSSC). Introduction of the organized mesoporous TiO2 layer resulted in the increased transmittance of visible light, decreased interfacial resistance and enhanced electron lifetime. As a result, an energy conversion efficiency of DSSC employing polymer electrolyte was significantly improved from 3.5% to 5.0% at 100 mW cm−2.

Improved Stability of Unsealed Quasi-Solid-State Dye-Sensitized Solar Cell Using Poly(3,4-Ethylenedioxythiophene) Film as Layer Electrolyte

Quasi-solid/solid polymer electrolytes have been the subject of extensive research for an alternative of liquid electrolyte for dye-sensitized solar cells (DSSCs) because of their advantages such as alleviated leakage, lower environmental impact and ease of device fabrication. In this work, the performance of the unsealed quasi-solid-state DSSCs based on composite poly (ethylene oxide) (PEO) electrolyte and N719 dye-sensitizer was examined on aging under atmospheric condition. The energy conversion efficiency of DSSC using the composite PEO electrolyte was 5.62 % under sun simulated light, AM 1.5 (100 mW cm-2) but gradually decreased to 0.95 % on aging for 90 days. An additional layer of poly(3,4-ethylenedioxythiophene) (PEDOT) electrolyte was incorporated with the composite polymer electrolyte for DSSC fabrication. The PEDOT layer was prepared by electrochemical polymerization of bis-ethylenedioxythiophene (bis-EDOT) and characterized by Raman spectroscopy and cyclic voltammetry. It was found that the energy conversion efficiency of DSSC based on the composite polymer electrolyte incorporated with PEDOT layer was 5.57 % and gradually decreased to 1.76 % under the same aging condition. Thus an additional layer of PEDOT electrolyte provided an improved stability of DSSC.