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Concept: Dye-sensitized solar cell


In this work, we report a direct synthesis of vertically aligned ZnO nanowires on fluorine-doped tin oxide-coated substrates using the chemical vapor deposition (CVD) method. ZnO nanowires with a length of more than 30 μm were synthesized, and dye-sensitized solar cells (DSSCs) based on the as-grown nanowires were fabricated, which showed improvement of the device performance compared to those fabricated using transferred ZnO nanowires. Dependence of the cell performance on nanowire length and annealing temperature was also examined. This synthesis method provided a straightforward, one-step CVD process to grow relatively long ZnO nanowires and avoided subsequent nanowire transfer process, which simplified DSSC fabrication and improved cell performance.

Concepts: Chromosome, Chemical reaction, Nanowire, Solar cell, Photovoltaics, Titanium dioxide, Dye-sensitized solar cell, Chemical vapor deposition


The wings of the black butterfly, Pachliopta aristolochiae, are covered by micro- and nanostructured scales that harvest sunlight over a wide spectral and angular range. Considering that these properties are particularly attractive for photovoltaic applications, we analyze the contribution of these micro- and nanostructures, focusing on the structural disorder observed in the wing scales. In addition to microspectroscopy experiments, we conduct three-dimensional optical simulations of the exact scale structure. On the basis of these results, we design nanostructured thin photovoltaic absorbers of disordered nanoholes, which combine efficient light in-coupling and light-trapping properties together with a high angular robustness. Finally, inspired by the phase separation mechanism of self-assembled biophotonic nanostructures, we fabricate these bioinspired absorbers using a scalable, self-assembly patterning technique based on the phase separation of binary polymer mixture. The nanopatterned absorbers achieve a relative integrated absorption increase of 90% at a normal incident angle of light to as high as 200% at large incident angles, demonstrating the potential of black butterfly structures for light-harvesting purposes in thin-film solar cells.

Concepts: Light, Structure, Refraction, Solar cell, Photovoltaics, Dye-sensitized solar cell, Thin film solar cell, Angle


Fabrication of thin-film solar cells (TFSCs) on substrates other than Si and glass has been challenging because these nonconventional substrates are not suitable for the current TFSC fabrication processes due to poor surface flatness and low tolerance to high temperature and chemical processing. Here, we report a new peel-and-stick process that circumvents these fabrication challenges by peeling off the fully fabricated TFSCs from the original Si wafer and attaching TFSCs to virtually any substrates regardless of materials, flatness and rigidness. With the peel-and-stick process, we integrated hydrogenated amorphous silicon (a-Si:H) TFSCs on paper, plastics, cell phone and building windows while maintaining the original 7.5% efficiency. The new peel-and-stick process enables further reduction of the cost and weight for TFSCs and endows TFSCs with flexibility and attachability for broader application areas. We believe that the peel-and-stick process can be applied to thin film electronics as well.

Concepts: Semiconductor, Silicon, Solar cell, Photovoltaics, Dye-sensitized solar cell, Thin film solar cell, Crystalline silicon, Amorphous silicon


Dye-sensitized solar cells based on titanium dioxide (TiO(2)) are promising low-cost alternatives to conventional solid-state photovoltaic devices based on materials such as Si, CdTe and CuIn(1-x)Ga(x)Se(2) (refs 1, 2). Despite offering relatively high conversion efficiencies for solar energy, typical dye-sensitized solar cells suffer from durability problems that result from their use of organic liquid electrolytes containing the iodide/tri-iodide redox couple, which causes serious problems such as electrode corrosion and electrolyte leakage. Replacements for iodine-based liquid electrolytes have been extensively studied, but the efficiencies of the resulting devices remain low. Here we show that the solution-processable p-type direct bandgap semiconductor CsSnI(3) can be used for hole conduction in lieu of a liquid electrolyte. The resulting solid-state dye-sensitized solar cells consist of CsSnI(2.95)F(0.05) doped with SnF(2), nanoporous TiO(2) and the dye N719, and show conversion efficiencies of up to 10.2 per cent (8.51 per cent with a mask). With a bandgap of 1.3 electronvolts, CsSnI(3) enhances visible light absorption on the red side of the spectrum to outperform the typical dye-sensitized solar cells in this spectral region.

Concepts: Electrochemistry, Semiconductor, Solar cell, Photovoltaics, Titanium dioxide, Electrolyte, Dye-sensitized solar cell, Germanium


The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co((II/III))tris(bipyridyl)-based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.

Concepts: Ultraviolet, Redox, Electrochemistry, Oxide, Solar cell, Titanium dioxide, Energy conversion, Dye-sensitized solar cell


We demonstrate four- and two-terminal perovskite-perovskite tandem solar cells with ideally matched band gaps. We develop an infrared-absorbing 1.2-electron volt band-gap perovskite, FA0.75Cs0.25Sn0.5Pb0.5I3, that can deliver 14.8% efficiency. By combining this material with a wider-band gap FA0.83Cs0.17Pb(I0.5Br0.5)3 material, we achieve monolithic two-terminal tandem efficiencies of 17.0% with >1.65-volt open-circuit voltage. We also make mechanically stacked four-terminal tandem cells and obtain 20.3% efficiency. Notably, we find that our infrared-absorbing perovskite cells exhibit excellent thermal and atmospheric stability, not previously achieved for Sn-based perovskites. This device architecture and materials set will enable “all-perovskite” thin-film solar cells to reach the highest efficiencies in the long term at the lowest costs.

Concepts: Solar cell, Photovoltaics, Direct current, Dye-sensitized solar cell, Thin film solar cell, Band gap, Photovoltaic array, Anwell Technologies Limited


Zinc zirconate (ZnZrO(3)) (ZZ), zinc oxide (ZnO) (ZO) and zirconium oxide (ZrO(2)) (ZRO) nano-particles were synthesized by simple sol-gel method. ZZ, ZO and ZRO nano-particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-Vis diffuse reflectance spectrum (DRS). Nanoporous ZZ, ZO and ZRO thin films were prepared doctor blade technique on the fluorine-doped tin oxide (FTO) and used as working electrodes in dye sensitized solar cells (DSSC). Their photovoltaic behavior were compared with standard using D35 dye and an electrolyte containing [Co(bpy)(3)](PF(6))(2), [Co(pby)(3)](PF(6))(3), LiClO(4), and 4-tert-butylpyridine (TBP). The properties of DSSC have been studied by measuring their short-circuit photocurrent density (Jsc), open-circuit voltage (VOC) and fill factor (ff). The application of ZnZrO(3) as working electrode produces a significant improvement in the fill factor (ff) of the dye-sensitized solar cells (ff=56%) compared to ZnO working electrode (ff=40%) under the same condition.

Concepts: Solar cell, Photovoltaics, Indium tin oxide, Titanium dioxide, Dye-sensitized solar cell, Thin film solar cell, Zinc oxide, Band gap


Ternary oxides are potential candidates as an electron-transporting material that can replace TiO(2) in dye-sensitized solar cells (DSSCs), as their electronic/optical properties can be easily controlled by manipulating the composition and/or by doping. Here, we report a new highly efficient DSSC using perovskite BaSnO(3) (BSO) nanoparticles. In addition, the effects of a TiCl(4) treatment on the physical, chemical, and photovoltaic properties of the BSO-based DSSCs are investigated. The TiCl(4) treatment was found to form an ultrathin TiO(2) layer on the BSO surface, the thickness of which increases with the treatment time. The formation of the TiO(2) shell layer improved the charge-collection efficiency by enhancing the charge transport and suppressing the charge recombination. It was also found that the TiCl(4) treatment significantly reduces the amount of surface OH species, resulting in reduced dye adsorption and reduced light-harvesting efficiency. The trade-off effect between the charge-collection and light-harvesting efficiencies resulted in the highest quantum efficiency (i.e., short-circuit photocurrent density), leading to the highest conversion efficiency of 5.5% after a TiCl(4) treatment of 3 min (cf. 4.5% for bare BSO). The conversion efficiency could be increased further to 6.2% by increasing the thickness of the BSO film, which is one of the highest efficiencies from non-TiO(2)-based DSSCs.

Concepts: Photoelectric effect, Chemistry, Solar cell, Photovoltaics, Titanium dioxide, Energy conversion, Dye-sensitized solar cell, P-n junction


A periodically aligned Pt nanocup array is employed as a counter electrode in dye-sensitized solar cells (DSSCs). The Pt nanocup array enhances the catalytic area, which results in a greater fill factor (FF) and higher short-circuit current (J(sc) ). A higher density of nanocups is preferable for the performance of DSSCs.

Concepts: Solar cell, Photovoltaics, Electrode, Dye-sensitized solar cell, Platinum, Fill factor


Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells because of their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanism in the gel electrolyte, and nanoclay interactions with TiO2/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion. The calculated physical diffusion coefficient shows that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in electrolyte has the effect of buffering the protonation process at TiO2/electrolyte interface, resulting in conduction band up-shift and a boost in Voc. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. 10 % improvement in the efficiency for hydrotalcite clay gel electrolyte is obtained, compared to that of the liquid electrolyte. The power conversion efficiency can be achieved as high as 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.  

Concepts: Electrochemistry, Physical chemistry, Solar cell, Titanium dioxide, Energy conversion, Energy conversion efficiency, Dye-sensitized solar cell, Thin film solar cell