Dye-sensitized solar cells (DSSCs) are regarded as prospective solar cells for the next generation of photovoltaic technologies and have become research hotspots in the PV field. The counter electrode, as a crucial component of DSSCs, collects electrons from the external circuit and catalyzes the redox reduction in the electrolyte, which has a significant influence on the photovoltaic performance, long-term stability and cost of the devices. Solar cells, dye-sensitized solar cells, as well as the structure, principle, preparation and characterization of counter electrodes are mentioned in the introduction section. The next six sections discuss the counter electrodes based on transparency and flexibility, metals and alloys, carbon materials, conductive polymers, transition metal compounds, and hybrids, respectively. The special features and performance, advantages and disadvantages, preparation, characterization, mechanisms, important events and development histories of various counter electrodes are presented. In the eighth section, the development of counter electrodes is summarized with an outlook. This article panoramically reviews the counter electrodes in DSSCs, which is of great significance for enhancing the development levels of DSSCs and other photoelectrochemical devices.

High saturation magnetization monodisperse Fe(3)O(4) hollow microspheres (109.48 emu/g) with superparamagnetic property at room temperature are promptly synthesized by a one-step solvothermal process with the presence of sodium dodecylbenzenesulfonate as an additive. The as-synthesized products possess superparamagnetism, large cavity, high water solubility, and saturation magnetization at room temperature. In particular, these hollow microspheres exhibit both of a rather short separation time from industry wastewater and a high adsorption capacity about 180 mg/g at high Cr(VI) concentrations, which is much better than those of reported magnetite solid nanoparticles. In addition, the X-ray photoelectron spectra (XPS) show that the uptake of Cr(VI) into the spheres was mainly governed by a physicochemical process. The micelle-assisted Ostwald ripening process was proposed to explain the rapid formation of hollow structures by a series of control experiments. The as-manufactured products with the two advantages mentioned above serve as ideal candidates for environmental remediation materials.

The porous hierarchical MgO with superb adsorption properties has been synthesized by a facile and scaled-up method. The X-ray powder diffraction, electron microscopy, Fourier transformed infrared, and N2 adsorption-desorption were carried out to study the microstructure of the as-synthesized precursor and product. It has been demonstrated that the as-prepared MgO has a porous hierarchical structure and a high specific surface area (148 m(2) g(-1)). And the MgO sample exhibited super adsorption properties, with maximum adsorption capacity of 2409 mg g(-1) for Congo red, which is the highest reported value. Moreover, the adsorption process of Congo red on porous hierarchical MgO was systematically investigated, which was found to obey the pseudo-second-order rate equation and Langmuir adsorption model.

A novel and efficient halogen-free composite flame retardant (CFR) consisting of a brucite core and a fine zinc borate [Zn6O(OH)(BO3)3] hierarchical nanostructure shell was designed and synthesized via a facile nanoengineering route. It had been demonstrated that this unique hybrid structure possessed a high BET specific surface area (65 m(2)/g) and could significantly enhance the interfacial interaction when mixing with ethylene-vinyl acetate (EVA). This improved the transfer of stress between CFR particles and EVA matrix and increased the viscosity of EVA/EVA blends, which was beneficial for droplet inhibition and char forming. The mechanical properties and flammability behaviors of the EVA/CFR blends had been compared with the EVA/physical mixture (PM, with the given proportion of brucite and Zn6O(OH)(BO3)3). The mechanical properties of EVA/CFR blends, especially the tensile strength (TS), presented a remarkable increase reaching at least a 20% increment. Meanwhile, with the same 45 wt % of fillers, the EVA/CFR formulation could achieve a limiting oxygen index (LOI) value of 33 (37.5 % higher than that of EVA/PM blends) and UL-94 V-0 rating. Moreover, the heat release rate (HRR), peak heat release rate (PHRR), total heat released (THR), smoke production rate (SPR) and mass loss rate (MLR) were considerably reduced, especially PHRR and SPR for EVA/CFR blends were reduced to 32%. According to this study, the design of fine structure might pave the way for the future development of halogen-free flame retardants combining both enhanced mechanical properties and excellent flame retardant behaviors.

Low loading is one of the bottlenecks limiting the performance of quantum dot sensitized solar cells (QDSCs). Although previous QD secondary deposition relying on electrostatic interaction can improve QD loading, due to the introduction of new recombination centers, it is not capable of enhancing the photovoltage and fill factor. Herein, without the introduction of new recombination centers, a convenient QD secondary deposition approach is developed by creating new adsorption sites via the formation of a metal oxyhydroxide layer around QD presensitized photoanodes. MgCl2 solution treated Zn–Cu–In–S–Se (ZCISSe) QD sensitized TiO2 film electrodes have been chosen as a model device to investigate this secondary deposition approach. The experimental results demonstrate that additional 38% of the QDs are immobilized on the photoanode as a single layer. Due to the increased QD loading and concomitant enhanced light-harvesting capacity and reduced charge recombination, not only photocurrent but also photovoltage and fill factor have been remarkably enhanced. The average PCE of resulted ZCISSe QDSCs is boosted to 15.31% (J sc = 26.52 mA cm–2, V oc = 0.802 V, FF = 0.720), from the original 13.54% (J sc = 24.23 mA cm–2, V oc = 0.789 V, FF = 0.708). Furthermore, a new certified PCE record of 15.20% has been obtained for liquid-junction QDSCs.

The photoelectronic properties of quantum dots (QDs) have a critical impact on the performance of quantum‐dot‐sensitized solar cells (QDSCs). Currently, I‐III‐VI group QDs have become the mainstream light‐harvesting materials in high‐performance QDSCs. However, it is still a great challenge to achieve satisfactory efficiency for light‐harvesting, charge extraction, and charge collection simultaneously in QDSCs. We design and prepare Zn0.4Cu0.7In1.0SxSe2−x (ZCISSe) quinary alloyed QDs by cation/anion co‐alloying strategy. The critical photoelectronic properties of target QDs, including band gap, conduction band energy level, and density of defect trap states, can be conveniently tailored. Experimental results demonstrate that the ZCISSe quinary alloyed QDs can achieve an ideal balance among light‐harvesting, photogenerated electron extraction, and charge‐collection efficiencies in QDSCs compared to its single anion or cation quaternary alloyed QD counterparts. Consequently, the quinary alloyed QDs boost the certified efficiency of QDSCs to 14.4 %, which is a new efficiency record for liquid‐junction QD solar cells.

Efficient ratiometric fluorescent Fe(3+) probes were designed and synthesized by linking a conjugated naphthalene chromophore to a rhodamine platform and a lipophilic triphenylphosphonium (TPP) cation. The probes could sensitively and selectively detect mitochondrial Fe(3+) in living cells.

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