Although efficiency of Dye Sensitized Solar Cell (DSSC) is still below the performance level of the market dominance silicon solar cells, in the last two decades DSSC has gathered sufficient ...interests because of the simplicity in device fabrication and low material cost, and therefore, DSSC is providing a possibility of solar cells production at a low entry cost. This review presents the research progress made in the implementation of natural pigments in DSSC. These pigments function as dye sensitizers and they play a major role in DSSC by absorbing light, and supplying electrons to the semiconductor matrixes in the cell. The common choices of dyes are the metal complexes, organic and/or natural dyes. A better efficiency with higher durability is observed for DSSC using metal complexes and organic dyes, however, the process of synthesizing these dyes is laborious, costly, and involves the use of toxic materials. As an alternative, natural pigments (dyes) found in plants such as anthocyanin, carotenoid, aurone, chlorophyll, tannin, betalain and many others are accepted as dyes in DSSCs. These natural pigments are easily obtained from fruits, flowers, leaves, seeds, barks and various parts of plants. Despite the limited performance of natural dyes, the prevailing advantages of natural dyes include high absorption coefficients, high light harvesting efficiency, low cost extraction and low toxicity. This review provides insight into the usage of the various natural pigments as sensitizers, the techniques to improve the pigments performance in DSSC, an outlook on the developmental work on the application of natural pigments in DSSC and their limitation. Additionally, the paper discusses the overall operation principle and the recent developments of each component of DSSC, as well as, comparing the material cost between natural dye and synthetic dye DSSC.
•Natural pigments have a promising future as sensitizers in DSSCs.•Anthocyanin, carotenoid, aurone, chlorophyll, tannin and betalain are among the natural pigments used as sensitizers.•Low-cost extraction, vast availability and eco-friendliness are major attractions of natural pigments.•The total fabrication cost for DSSC sensitized with chlorophyll is less than ~€ 2 per Watt peak.
Low power consumption, fast response and quick recovery times are important parameters for gas sensors performance. Herein, we report the experimental and theoretical studies of ZnO and Cr doped ZnO ...nanostructures used in low temperature (50 °C) sensors for the detection of CO. The synthesized films were characterized by XRD, UV-Vis, FE-SEM and EDX. The XRD patterns for the ZnO and 0.5 wt% Cr/ZnO films confirm the formation of a single-phase hexagonal wurtzite structure. The reduction of the ZnO optical band gap from 3.12 eV to 2.80 eV upon 0.5 wt% Cr doping is well correlated with the simulation data. The FE-SEM images of the films show spherical morphology with the estimated particle sizes of about ~40 nm and ~ 25 nm were recorded for the ZnO and 0.5 wt% Cr/ZnO films, respectively. Enhanced gas sensing performance is achieved with Cr doping and the sensitivity of ZnO increases from 9.65% to 65.45%, and simultaneously decreasing the response and recovery times from 334.5 s to 172.3 s and from 219 s to 37.2 s, respectively. These improvements in gas sensing performance are due to the reduction in particle size and optical band gap, and an increase in specific surface area.
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•Doping of mesoporous TiO2 layers with Al and Mg to improve PCEs of PSCs.•Al doping eliminates deep trap sites in lattice and decreases band gap of TiO2.•JSC, VOC, and FF increase in ...PSCs with Al doped mesoporous TiO2.•Mg doping increases band gap of TiO2; VOC increases in PSCs with Mg doped TiO2.
In this work, we investigate how Al and Mg doped mesoporous TiO2 layers can improve the power conversion efficiency (PCE) of perovskite solar cells (PSCs) with respect to undoped mesoporous TiO2. The PSC configuration used in this study consists of mesoscopic structure with CH3NH3PbI3 as the perovskite absorber. A PSC with optimized mol% of Al and Mg doped mesoporous TiO2 layers has been shown to achieve up to 22% higher efficiency than that of pure TiO2. While the Mg doping only enhances the open-circuit voltage (VOC), the Al doping effectively enhances the VOC, the short-circuit current density (JSC), and the fill factor (FF). The occupancy of the doped metals in the lattice is confirmed by XRD, EDX, and XPS. The Mg doping increases the band gap of TiO2 while the Al doping decreases it. The wide band gap in Mg doped TiO2 reduces the electron and hole recombination rate, thus increasing the JSC and VOC. By Al doping, deep trap sites in the TiO2 are eliminated, and this effectively reduces the recombination losses and in turn, increases the JSC. The enhanced electron-hole generation rate attributed to the decrease in the band gap of Al doped TiO2 also increases the JSC. In addition, there is an enhancement on the electron mobility by the presence of Al metal and this gives an increase in the FF. The results have demonstrated the possibility of improving the PCE of PSCs by fine tuning the band gap of mesoporous TiO2.
Abstract
Herein, we design a high sensitivity with a multi-mode plasmonic sensor based on the square ring-shaped resonators containing silver nanorods together with a metal–insulator-metal bus ...waveguide. The finite element method can analyze the structure's transmittance properties and electromagnetic field distributions in detail. Results show that the coupling effect between the bus waveguide and the side-coupled resonator can enhance by generating gap plasmon resonance among the silver nanorods, increasing the cavity plasmon mode in the resonator. The suggested structure obtained a relatively high sensitivity and acceptable figure of merit and quality factor of about 2473 nm/RIU (refractive index unit), 34.18 1/RIU, and 56.35, respectively. Thus, the plasmonic sensor is ideal for lab-on-chip in gas and biochemical analysis and can significantly enhance the sensitivity by 177% compared to the regular one. Furthermore, the designed structure can apply in nanophotonic devices, and the range of the detected refractive index is suitable for gases and fluids (e.g., gas, isopropanol, optical oil, and glucose solution).
•Mg-La, Ca-La and Al-La co-doped TiO2 were synthesized respectively at 0.5mol%.•Small ionic radius ions enter TiO2 lattice and led to increased recombination rate.•Larger Ca2+ ions result in an ...increased electron transport.•Despite low efficiency, 0.5mol% Al-La TiO2 displayed the highest fill factor.
Doping is a method whereby small amounts of impurities are introduced into the lattice of a material and is employed for improving the efficiency of dye-sensitized solar cells (DSSCs) via modification of the semiconductor material. Co-doping, which involves doping with more than one type of impurity, is typically used over doping owing to its unique effects on the short-circuit current and open-circuit voltage; the different types of added impurities can exert a synergy effect in enhancing the performance of DSSCs. Of particular interest is the study of the effects of the ionic radii of co-dopants on the performance of DSSCs that is not well understood to date. Thus, in this paper, TiO2 was co-doped with lanthanum and magnesium, calcium, or aluminium at respective contents of 0.5mol%. The co-doped TiO2 and pure TiO2 powders were prepared by sol–gel. Mg-La co-doped TiO2-based DSSC displayed the highest efficiency (i.e., 6.60%) and Al-La co-doped TiO2-based DSSC displayed the lowest efficiency. Among the dopants studied herein, aluminium ion has the smallest ionic radius. Thus, aluminium ions could easily enter the lattice structure of TiO2, generating a high concentration of holes that led to the decrease of electron transport and photocurrent, hence lower DSSC efficiency.
In this study, density functional theory (DFT) was used to investigate the influence of temperature on the performance of a novel Cu-nitrogen-doped graphene Cu
-N
/Gr nanocomposite as a catalyst for ...the oxygen reduction reaction (ORR) in fuel cell applications. Our DFT calculations, conducted using Gaussian 09w with the 3-21G/B3LYP basis set, focus on the Cu-nitrogen-doped graphene nanocomposite cathode catalyst, exploring its behavior at three distinct temperatures: 298.15 K, 353.15 K, and 393.15 K, under acidic conditions. Our analysis of formation energies indicates that the structural stability of the catalyst remains unaffected as the temperature varies within the potential range of 0-7.21 V. Notably, the stability of the ORR steps experiences a marginal decrease with increasing temperature, with the exception of the intermediate OH + H
O (*OH + H + *OH). Interestingly, the optimization reveals the absence of single OH and H
O intermediates during the reactions. Furthermore, the OH + H
O step is optimized to form the OH + H + OH intermediate, featuring the sharing of a hydrogen atom between dual OH intermediates. Free energy calculations elucidate that the catalyst supports spontaneous ORR at all temperatures. The highest recorded maximum cell potential, 0.69 V, is observed at 393.15 K, while the lowest, 0.61 V, is recorded at 353.15 K. In particular, the Cu
-N
/Gr catalyst structure demonstrates a reduced favorability for the H
O
generation at all temperatures, resulting in the formation of dual OH intermediates rather than H
O
. In conclusion, at 393.15 K, Cu
-N
/Gr exhibits enhanced catalyst performance compared to 353.15 K and 298.15 K, making it a promising candidate for ORR catalysis in fuel cell applications.
•The structural, optical and optoelectronic properties of 1mol.% Fe, Sn and Cu doped TiO2 have been compared.•Transient lifetimes for pure TiO2 and Sn doped TiO2 were considerably shorter than Fe and ...Cu doped TiO2.•A good correlation between the bulk defects and transient decay for the doped TiO2 powders was observed.•Photon to current conversion efficiency of DSSC based on the metal doped TiO2 were in order Sn-TiO2>Cu-TiO2>Pure>>Fe-TiO2.•DSSC based on Fe doped photoanodes is limited by a high concentration of surface free holes observed at 433nm.
Electron transfer dynamics in the oxide layers of the working electrodes in both dye-sensitized solar cells and photocatalysts greatly influences their performance. A proper understanding of the distribution of surface and bulk energy states on/in these oxide layers can provide insights into the associated electron transfer processes. Metal ions like Iron (Fe), Copper (Cu) and Tin (Sn) doped onto TiO2 have shown enhanced photoactivity in these processes. In this work, the structural, optical and transient properties of Fe, Cu and Sn doped TiO2 nanocrystalline powders have been investigated and compared using EDX, Raman spectroscopy, X-ray Photoelectron spectroscopy (XPS), and Transient Absorption spectroscopy (TAS). Surface free energy states distributions were probed using Electrochemical Impedance spectroscopy (EIS) on Dye Sensitized Solar Cells (DSSC) based on the doped TiO2 photoanodes. Raman and XPS Ti2p3/2 peak shifts and broadening showed that the concentration of defects were in the order: Cu doped TiO2>Fe doped TiO2>Sn doped TiO2>pure TiO2. Nanosecond laser flash photolysis of Fe and Cu doped TiO2 indicated slower transient decay kinetics than that of Sn doped TiO2 or pure TiO2. A broad absorption peak and fast transient decay at 430nm for Fe doped TiO2 was ascribed to an increase in surface hole concentration resulting in poor current density in the Fe doped TiO2 photoanodes relative to pure TiO2, Sn or Cu doped anodes. The charge transfer capacitance and the calculated electron lifetimes correlated well with the trend in current density of the photoanodes (Sn>Cu>pure TiO2). The poor performance of Fe doped cells is due to faster recombination of injected electrons with surface holes while those of Sn and Cu were more influenced by the concentration of their bulk defects. These results demonstrate that the choice of selected metal ions doping onto TiO2 for a desired application should take into consideration the influence of bulk defect concentrations, the energy state distribution and the electron transfer properties in/on the oxide photoanodes.
•An easy and robust method to construct the substrate for PL-based detection and plasmon-enhanced photoluminescence (PL) is proposed.•The enhanced magnitude of the EM waves exhibited tunable PL ...activities with Raman intensity on the order of 1 × 104.•Experimental results show that PL enhancement value of 15.69 times higher than that of pure DCJTB layer, and the life time is shortened from 0.97 ns to 0.41 ns.
We have fabricated Ag-SiO2 core–shell nanostructure set in the hexagonally ordered Ag nanohole array by nanosphere lithography with reactive ion etching, and followed by Ag deposition. The resulting nanostructure includes the triangular-shaped plates with sharp edges on the top, the Ag-SiO2 core–shell nanospheres, the hexagonally arranged nanohole array, a SiO2 buffer layer and a DCJTB (4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) fluorescent dye layer, respectively. Six patterns of substrates (i.e., Types 1–6) were fabricated and their photoluminescence enhancement performance was compared to substrate layered with pure DCJTB. The experimental results show that photoluminescence enhancement can be 15.69 times, and the lifetime can be shortened from 0.97 ns to 0.41 ns for Type 3 when compared to the pure DCJTB one. The finite element method revealed four structure conditions which are the effects of edge enhancement, gap plasmon resonance, hollow plasmon resonance, and core–shell hybridization plasmon resonance and can contribute to the photoluminescence enhancement factor. The proposed substrates provide a practical detecting platform with plasmon-enhanced photoluminescence, and the fabrication methods used are technically simple and low cost.
We numerically and theoretically investigate a highly sensitive and tunable plasmonic refractive index sensor that is composed of a metal-insulator-metal waveguide with a side-coupled nanoring, ...containing silver nanorods using the finite element method. Results reveal that the presence of silver nanorods in the nanoring has a significant impact on sensitivity and tunability performance. It gives a flexible way to tune the system response in the proposed structure. Our designed sensor has a sensitivity of 2080 nm/RIU (RIU is the refractive index unit) along with a figure of merit and a quality factor of 29.92 and 29.67, respectively. The adequate refractive index sensitivity can increase by adding the silver nanorods in a nanoring, which can induce new surface plasmon polaritons (SPPs) modes that cannot be found by a regular nanoring. For a practical application, a valid introduction of silver nanorods in the nanoring can dramatically reduce the dimension of the proposed structure without sacrificing performance.
In this study, locally grown bamboo (Gigantochloa spp.) was used as feedstock for pyrolysis production of biochar under various pyrolysis temperatures (400–800°C). The resultant biochars were tested ...for their performance in adsorptive removal of the methylene blue (MB) dye. The scope of the adsorption experiment includes the effects of adsorbent dosage, solution pH, initial adsorbate concentration, and contact time. The adsorption data confirmed that pyrolysis temperature has a significant effect on adsorptive performance, whereas biochar pyrolysed at 500°C (BC500) has the highest adsorptive performance with the maximum adsorption capacity (derived from the Langmuir model) being 86.6 mg g-1. Basic characterisations (SEM, EDX, XRD, FTIR, and BET) were carried out for BC500 where FTIR and SEM confirmed the adsorption of MB onto the biochar, while the BET data showed the reduction of the BET surface area, total pore volume, and pore diameter after the adsorption process.
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