Photovoltaic Properties Of Dye-sensitized Solar Cells Research Articles

Photovoltaics and its magnetic-field promotion effect in dye-sensitized solar cells with BiFeO3 + TiO2 composite photoanodes

In dye-sensitized solar cells (DSSCs), the light absorbance of photoanode is the most important factor in power conversion efficiency (PCE). Here the authors report on an alternative modified TiO2-based photoanode for obtaining enhanced photovoltaic (PV) properties in DSSCs. Multiferroics BiFeO3, which possesses excellent magnetic, electric, and photocatalytic performances, was employed to construct BiFeO3 + TiO2 composite photoanode for DSSCs. In this type of DSSCs with BiFeO3 + TiO2 composite photoanodes, BiFeO3 with suitable bandgap may also act as photoelectric conversion medium, which is generally acted by dye in DSSCs, and increases photogenerated carrier transport channels, which improves the PCE of DSSCs with BiFeO3 + TiO2 composite photoanodes. More importantly, magnetic-field enhanced PV properties in abovementioned DSSCs was firstly obtained, which may result from magnetic-field-suppression the recombination of charge carriers and magnetoresistance effect in BiFeO3. The investigated results offer both an alternative method to improve PV properties in DSSCs, and a referential train of thought to manipulate photoelectric properties of solar cells.

Correlation between anodization variables and surface properties of titania nanotube arrays for dye-sensitized solar cells

Abstract The effect of anodization variables on the morphology and surface properties of oriented titania nanotube arrays (TNAs) was investigated. The arrays were synthesized using hydrofluoric acid based ethylene glycolelectrolyte. The results show that the anodization time plays a significant role in the surface properties as well as length of the nanotubes. However, the contribution of anodization potential to debris formation was found to be negligible within the investigated range of the potential. The F− ion concentration and aging of electrolyte were found to play crucial roles in the formation of ordered clean nanotubes. The studies conducted by employing these TNAs as photo-anodes for dye-sensitized solar cells (DSCs) show that the morphology variations alone alter the photovoltaic properties of DSCs to a great extent.

The Effect of Heteroleptic Dual Acceptors on Dye-Sensitized Solar Cells

A novel carbazole-based organic dye with heteroleptic dual electron acceptors (cyanoacrylic acid and thieno[3,4-b]pyrazine acid) on each side of a quinoxaline was designed, and its electronic and optical properties were investigated theoretically for dye-sensitized solar cells (DSSCs). To gain insight into the factors responsible for photovoltaic efficiency, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations of these dyes were performed. The absorption spectrum of the dyes showed different forms because of the different energy levels of the molecular orbital (MO) of each dye and the intramolecular energy transfer (EnT). Considering the overall properties, the asymmetric organic dye containing the heteroleptic dual acceptors showed a competitive conversion efficiency, greater red-shift, broader absorption spectra, and higher molar extinction coefficient compared to a single acceptor in the conversion efficiency of the DSSCs. These results indicate that heteroleptic dual acceptors produces good photovoltaic properties for DSSC.

Novel Quinoxaline-Based Organic Dye with Heteroleptic Dual Electron Donor for Dye-Sensitized Solar Cells.

A novel quinoxaline-based organic dye with heteroleptic dual electron donors (phenoxazine and carbazole) on each side of a quinoxaline was designed, and its electronic and optical properties were investigated theoretically for applications to dye-sensitized solar cells (DSSCs). To understand the factors influencing the photovoltaic efficiency, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations of these dyes were performed. The absorption spectrum of the dyes showed different forms because of the different energy levels of the molecular orbital (MO) of each dye and the intramolecular charge-transfer (ICT) characteristics. The asymmetric organic dye with the heteroleptic dual donor showed competitive conversion efficiency, greater red-shift, broader absorption spectra, and higher molar extinction coefficient compared to dyes with homoleptic dual donors. These results indicate that adding a withdrawing unit and heteroleptic donor produces good photovoltaic properties for DSSCs.

Preparation of polypyrrole/multi-walled carbon nanotube hybrids by electropolymerization combined with a coating method for counter electrodes in dye-sensitized solar cells

In this work, multi-wall carbon nanotubes coated with polypyrrole (PPy/MWCNT) have been used as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). PPy was deposited onto fluorine-doped tin-oxide-coated glass by electrochemical polymerization of pyrrole. Three surfactants were used in the preparation of the hybrids: cationic cetyltrimethylammonium bromide, anionic sodium dodecylbenzenesulfonate (DBSNa), and non-ionic polyoxyethylene sorbitan monolaurate (Tween20). The morphologies of the PPy and PPy/MWCNT hybrids were investigated using scanning electron spectroscopy. Chemical composition of the prepared CEs was determined by X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy. The catalytic activity of the PPy and PPy/MWCNT layers was evaluated using cyclic voltammetry, and the photovoltaic properties of DSSCs with PPy and PPy/MWCNT CEs were characterized using I–V measurements. PPy/MWCNT samples that were prepared by electrochemical polymerization showed the best results when the anionic surfactant DBSNa was used during polymerization. The photoelectric conversion efficiency of PPy/MWCNT prepared by electrochemical polymerization was 2.9%, which was 59% of that of Pt CE (4.9%).

Theoretical study of tribranched organic sensitizer for Efficient Dye-sensitized solar cells

ABSTRACTWe investigated the effect of heteroleptic dual electron acceptor as a photosensitizer for the dye-sensitized solar cells (DSSCs). Novel tribranched organic dyes were designed with heteroleptic dual electron acceptors [cyanoacrylic acid (R1), and indolinum carboxyl acid (R2)] on each side of a triazine (TRZ) based organic dye and triphenylamine and the additional phenothiazine as an antenna group for DSSCs. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to estimate the photovoltaic properties of the dyes. The absorption spectrum of the dyes showed different forms because of the different energy levels of molecular orbital (MO) of each dye and intramolecular energy transfer. Considering overall properties, the asymmetric tribranched organic dye exhibited a high conversion efficiency performance for DSSCs. The findings of this work suggest that optimizing the branch of electron donors and acceptors in dye sensitizers based on asymmetric tribranched organic dye produces good photovoltaic properties for DSSCs.

Improved performance of dye sensitized solar cell via fine tuning of ultra-thin compact TiO2 layer

The role of properties of ultra-thin TiO2 compact layers (c-TiO2) deposited on fluorine-doped tin oxide (FTO) substrates, as a function of their thickness, has been studied by using electrochemical and optical techniques as well as surface morphology. The performance of films of thicknesses varying from 7nm to 20nm was compared with TiO2 films having a constant thickness (7nm) prepared with different precursor concentrations. The surface morphology of the compact layer was investigated using field emission scanning electron microscope (FESEM) and it was observed that a film thickness less than 10nm was sufficient to serve as a compact layer in the fabrication of dye sensitized solar cells (DSSCs). The power conversion efficiency (ɳ) of devices was found to be similar for a compact layer of thickness of 10nm and observed to degrade for thicknesses >10nm. This was attributed to the combined effect of optical transmittance, morphology, conductivity and position of Fermi level. Further, for devices prepared with compact layer of constant thickness (7nm), a significant improvement in the ɳ (5.2%) is obtained for DSSCs prepared using 10mM precursor concentration. The improvement in the ɳ is attributed to the facile transport as well as proper position of Fermi level without compromising optical and morphological properties. The analyses suggest that properties of the thin TiO2 compact layer play a significant role in the photovoltaic properties of DSSCs.

One-dimensional TiO2 nanostructured photoanode for dye-sensitized solar cells by hydrothermal synthesis

One-dimensional nanostructured photoanode in the dye-sensitized solar cell (DSSC) provides better electron transport and lifetime. One-dimension TiO2 nanostructures (1D-TNs) were prepared by single-step hydrothermal synthesis for 10 h using titanium(IV) isopropoxide (TTIP) and titanium(IV) chloride (TiCl4) as the precursor. Nano parallelepiped TiO2 film was uniformly grown on the substrate which was ball milled to increase the specific surface area to felicitate sufficient dye-loading for efficient DSSC. The synthesized nanostructures were characterized by scanning and transmission electron microscopy and X-ray diffraction. Photovoltaic properties of DSSC with prepared TiO2 1D-TNs as the active layer, N719 dye and Pt counter electrode was investigated. The power conversion efficiency of the prepared cells was measured by using solar simulator under standard test conditions (100 mW/cm2, AM 1.5). The cell performance can be maximized by optimizing the thickness of 1D-TNs photoanode. The promising power conversion efficiency of 5.77% was obtained with the photoanode of 5 μm thickness.

Effect of sulfur doped TiO2 on photovoltaic properties of dye-sensitized solar cells

In a dye-sensitized solar cell (DSC), a nano-porous semiconductor layer plays an important role in the performance. It determines open-circuit voltage and it affects the dye adsorption capacity and charge transfer, which are closely associated with photocurrent and overall performance. TiO2 is the most proper material for nano-porous layer since the first development of DSCs. This work focuses on the enhancement of TiO2 by doping. Sulfur (S) doping enhances charge transfer and the photoconversion of TiO2. Therefore, the increase in photocurrent and efficiency is expected by S doping. S is doped into TiO2 by hydrolysis method. The amount of S is varied and their photo-responses are verified. The most effective S doped TiO2 is applied to DSCs. Overall performance of DSC is enhanced by the addition of S doped TiO2. Especially, the photocurrent is much increased by the improvement on charge transfer, electron lifetime, and photo-conversion. The photovoltaic properties of DSCs are investigated with various ratios of undoped and S doped TiO2. Finally, a DSC based on undoped and S doped TiO2 ratio of 1:1 has the highest efficiency, better than that of a standard DSC based on undoped TiO2.

Dye-Sensitized Solar Cells Using Natural Dyes Extracted From Plumeria and Celosia Cristata Flowers

In this study, extracted plumeria and celosia cristata flowers have been used as the sensitizer for dye-sensitized solar cells (DSSC). The cells were fabricated using TiO2 as a semiconductor layer deposited on transparent Indium doped tin oxide (ITO) conductive glass using a spin coating technique. The films with dyes were characterized by UV-VIS absorption spectra. The photovoltaic properties of DSSC were studied under an incident irradiation of 100 mW/cm2. The I-V characteristic curves of all fabricated cells were measured and analysed. The energy conversion efficiency (η) of the cells consisting of plumeria extract and celosia cristata extract was 3.73 × 10-6 and 1.18 × 10-7, respectively.

Dye-Sensitized Solar Cells Using Natural Dyes Extracted From Plumeria and Celosia Cristata Flowers

In this study, extracted plumeria and celosia cristata flowers have been used as the sensitizer for dye-sensitized solar cells (DSSC). The cells were fabricated using TiO2 as a semiconductor layer deposited on transparent Indium doped tin oxide (ITO) conductive glass using a spin coating technique. The films with dyes were characterized by UV-VIS absorption spectra. The photovoltaic properties of DSSC were studied under an incident irradiation of 100 mW/cm2. The I-V characteristic curves of all fabricated cells were measured and analysed. The energy conversion efficiency (η) of the cells consisting of plumeria extract and celosia cristata extract was 3.73 × 10-6 and 1.18 × 10-7, respectively.

Characteristics of charge transport in nano-sized TiO2 particles/submicron spheres multilayer thin-film electrode

In this work, we design the nano-sized TiO2 particles/submicron spheres multilayer structured photoanode, based on the fact of stronger light scattering properties of TiO2 submicron spheres. Effect of TiO2 submicron-spheres on the charge transport and interfacial properties in multilayer thin-film electrodes are investigated in detail using intensity-modulated photocurrent spectroscopy (IMPS), electrochemical impedance spectroscopy (EIS) and incident photon-to-current conversion efficiency (IPCE). Results obtained from IMPS for dye-sensitized solar cells (DSCs) indicate that submicron-spheres have fewer defects, but the poor contact at the interfaces between submicron spheres hinders the electron transport and makes the transit time longer. EIS results show that there are no obvious differences in interface recombination between the designed electrodes. It is interesting to find that the bottom section of the photoanode composed of nano-sized TiO2 thin film has a higher light utilization efficiency than that composed of submicron-spheres; meanwhile, the Fermi level of TiO2 and the photovoltaic properties of DSCs have been extended. Our results may provide an experiment basis for structure design of high-efficiency DSC photoanode.

The effect of ethylene glycol/citric acid molar ratio in the initial precursor of TiO2 nanoparticle paste synthesized by a polymerizable complex method on the photovoltaic properties of dye-sensitized solar cells

A polymerizable complex method, also known as a Pechini method, was employed to synthesize titanium-sol (Ti-sol) as a matrix for TiO2 nanoparticle paste, suitable for fabrication of semiconducting mesoporous TiO2 layer as a photoanode of dye-sensitized solar cells (DSSCs). The purpose of the present work was to investigate the effect of ethylene glycol (EG)/citric acid (CA) molar ratio (Z), in the initial Ti-sol precursor, on the photovoltaic properties of DSSCs. From viscosity (µ) measurement and Fourier transform infrared (FTIR) spectrum of Ti-sols it was revealed that the amount of polyester in the sol decreases with increasing Z. The higher polyester content in the Ti-sols with lower Z ratios led to their higher surface tension (γ) and as a result the higher contact angle (α). The low wettability of fluorine doped tin oxide (FTO) coated glass with Ti-sol was the main reason of micro-cracking of TiO2 layers after sintering. This effect was significant for lower Z ratios. Micro-cracks increase the back electron–hole recombination rate. Also, at higher Z ratio, the back electron–hole recombination rate increased, which was due to the lower Ti4+ ions in the Ti-sol precursor and poor interconnection between TiO2 nanoparticles. Therefore, the maximum short circuit current density (Isc) and the maximum conversion efficiency (η) were obtained for Z=4. Fill factor (FF) decreased with increasing Z. But, open circuit voltage (Voc) was nearly independent of Z.

Influence of iodide source on the performance of liquid and silica nanoparticle-loaded quasi-solid electrolyte-based dye-sensitized solar cells

Presence of cations from iodide source in liquid electrolyte has strong influence on photoelectrochemical characteristics of dye-sensitized solar cells (DSSCs). The present work shows the effect of different cations in liquid and silica-loaded gel electrolyte on the photovoltaic properties of DSSCs. Zeta potential measurements have been carried out to probe into the adsorption behavior of ions. It has been found out that lithium ions being smaller in size as compared to 1-methyl-3-propylimidazolium and tetrabutylammonium ions effectively get adsorbed onto the surface of silica nanopowder. Liquid and gel electrolytes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In DSSCs, it was found that silica nanopowder addition to lithium ions-based liquid electrolyte significantly increases the open-circuit voltage as compared to the other two ions used in the study. This is due to adsorption of lithium ions onto silica surface which retards such ions to intercalate into or adsorb onto titania.

강유전체 BiFeO3가 증착된 TiO2전극을 이용한 염료감응형 태양전지의 효율 향상

Dye-sensitized solar cells (DSSCs) based on titanium dioxide (<TEX>$TiO_2$</TEX>) have been extensively studied because of their promising low-cost alternatives to conventional semiconductor based solar cells. DSSCs consist of molecular dye at the interface between a liquid electrolyte and a mesoporous wide-bandgap semiconductor oxide. Most efforts for high conversion efficiencies have focused on dye and liquid electrolytes. However, interface engineering between dye and electrode is also important to reduce recombination and improve efficiency. In this work, for interface engineering, we deposited semiconducting ferroelectric <TEX>$BiFeO_3$</TEX> with bandgap of 2.8 eV on <TEX>$TiO_2$</TEX> nanoparticles and nanotubes. Photovoltaic properties of DSSCs were characterized as a function of thickness of <TEX>$BiFeO_3$</TEX>. We showed that ferroelectric <TEX>$BiFeO_3$</TEX>-coated <TEX>$TiO_2$</TEX> electrodes enable to increase overall efficiency of DSSCs, which was associated with efficient electron transport due to internal electric field originating from electric polarization. It was suggested that engineering the dye-<TEX>$TiO_2$</TEX> interface using ferroelectric materials as inorganic modifiers can be key parameter for enhanced photovoltaic performance of the cell.

Synergistic effects of the aspect ratio of TiO2 nanowires and multi-walled carbon nanotube embedment for enhancing photovoltaic performance of dye-sensitized solar cells

The existence of numerous interfacial boundaries among TiO2 nanoparticles (NPs) accumulated in the photoelectrode layer of dye-sensitized solar cells (DSSCs) hinders the effective transport of photogenerated electrons to an electrode. Therefore, as a replacement for TiO2 NPs, one-dimensional TiO2 nanowires (NWs) can be suggested to provide pathways for fast electron transport by significantly reducing the number of interfacial boundaries. In order to provide direct evidence for the better performance of such longer TiO2 NWs than shorter TiO2 NWs, we examine the effect of the controlled aspect ratio of the TiO2 NWs randomly accumulated in the photoelectrode layer on the photovoltaic performance of DSSCs. It is clearly found that longer TiO2 NWs significantly improve the electron transport by reducing the TiO2/dye/electrolyte interfacial contact resistance. Furthermore, the embedment of multi-walled carbon nanotubes (MWCNTs) as an effective charge transfer medium in longer TiO2 NWs is proposed in this study to promote more synergistic effects, which lead to significant improvements in the photovoltaic properties of DSSCs.

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.