Quantum dot-sensitized solar cells

Quantum dot-sensitized solar cells (QDSCs) have emerged as a promising candidate for next-generation solar cells due to the distinct optoelectronic features of quantum dot (QD) light-harvesting materials, such as high light, thermal, and moisture stability, facilely tunable absorption range, high absorption coefficient, multiple exciton generation possibility, and solution processability as well as their facile fabrication and low-cost availability. In recent years, we have witnessed a dramatic boost in the power conversion efficiency (PCE) of QDSCs from 5% to nearly 13%, which is comparable to other kinds of emerging solar cells. Both the exploration of new QD light-harvesting materials and interface engineering have contributed to this fantastically fast improvement. The outstanding development trend of QDSCs indicates their great potential as a promising candidate for next-generation photovoltaic cells. In this review article, we present a comprehensive overview of the development of QDSCs, including: (1) the fundamental principles, (2) a history of the brief evolution of QDSCs, (3) the key materials in QDSCs, (4) recombination control, and (5) stability issues. Finally, some directions that can further promote the development of QDSCs in the future are proposed to help readers grasp the challenges and opportunities for obtaining high-efficiency QDSCs

Efficient perpendicular magnetization switching by a magnetic spin Hall effect in a noncollinear antiferromagnet

Current induced spin-orbit torques driven by the conventional spin Hall effect are widely used to manipulate the magnetization. This approach, however, is nondeterministic and inefficient for the switching of magnets with perpendicular magnetic anisotropy that are demanded by the high-density magnetic storage and memory devices. Here, we demonstrate that this limitation can be overcome by exploiting a magnetic spin Hall effect in noncollinear antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows generation of the out-of-plane spin current carrying spin polarization collinear to its direction induced by an in-plane charge current. This spin current drives an out-of-plane anti-damping torque providing the deterministic switching of the perpendicular magnetization of an adjacent Ni/Co multilayer. Due to being odd with respect to time reversal symmetry, the observed magnetic spin Hall effect and the resulting spin-orbit torque can be reversed with reversal of the antiferromagnetic order. Contrary to the conventional spin-orbit torque devices, the demonstrated magnetization switching does not need an external magnetic field and requires much lower current density which is useful for low power spintronics

Effect of Deep Cryogenic Treatment on the Artificial Ageing Behavior of SiCp–AA2009 Composite

The effect of deep cryogenic treatment (DCT) on the artificial ageing kinetics of a SiC particles reinforced aluminum alloy composite (SiCp-Al) is experimentally studied in this paper. The evolutions of both macro-properties (i.e., yield strength and ultimate tensile strength) and microstructures (precipitates) have been investigated by a set of hardness tests, tensile tests, and microstructural observations (scanning electron microscope, SEM and transmission electron microscope, TEM) for a SiCp-Al composite material with conventional heat treatment (solution heat treatment + quenching + artificial ageing, CHT) or DCT (solution heat treatment + quenching + deep cryogenic + artificial ageing). The results show that SiCp could significantly accelerate the ageing kinetics of the composites. Meanwhile, compared with CHT conditions, DCT can further improve the yield strength (YS) and ultimate tensile strength (UTS) of the composite materials after artificial ageing. The microstructures show that DCT induces the generation of more thinner θ′ precipitates homogeneously distributed in the grains during artificial ageing compared with corresponding CHT conditions. A quantified analysis has been performed based on the microstructural data, and the calculated results further support the indication that the strengthening effect in DCT compared with CHT is mainly contributed by corresponding precipitation behavior

Metal-Organic Framework-Derived Sea-Cucumber-like FeS2@C Nanorods with Outstanding Pseudocapacitive Na-Ion Storage Properties

Sodium-ion batteries (SIBs) are supposed to be attractive energy strorage and supply devices due to the abundant reserves of sodium. Their limited specific capacity and rate capacity, however, are standing in the way of the extensive application of SIBs. It is reported herein that porous sea-cucumber-like FeS2@C nanorods can act as efficient cathode materials to satisfy the rigorous requirements of the proposed applications. The fabrication of the sea-cucumber-like FeS2@C nanorods involves the hydrothermal growth of F-MIL (where F = Fe, MIL = materials from the Lavoisier Institute) nanorods, and subsequent sulfidation. The electrochemical results demonstrate that the FeS2@C nanorods are an outstanding cathode material for SIBs with high specific capacity (385 mAh/g), ultralong lifetime (160 mAh/g after 10 000 cycles at 20 A/g), and exceptional rate capability. The metal−organic framework (MOF) template method provides a useful route toward the development of high-performance electrode materials with robust power and cyclability

3D spongy CoS2nanoparticles/carbon composite as high-performance anode material for lithium/sodium ion batteries

A spongy CoS 2 /carbon composite assembled from CoS 2 nanoparticles (∼20 nm) homogeneously anchored on a spongy carbon matrix was synthesized through a facile freeze-drying method and a hydrothermal process. As anode material for lithium/sodium ion batteries (LIBs/SIBs), this composite shows significantly enhanced lithium/sodium storage performance with the synergetic effects due to the electrical conductivity of the carbon matrix and the porous structure, which provide buffer spaces for volume expansion during charge/discharge processes and feasible transfer pathways for electrons/ions. The electrochemical results demonstrate that the spongy CoS 2 /carbon composite is an outstanding anode material for LIBs and SIBs. It delivers a high specific capacity of 610 mAh g −1 at 500 mA g −1 after 120 cycles in LIBs and 330 mAh g −1 at 500 mA g −1 after 60 cycles in SIBs, respectively. Moreover, the freeze-drying/hydrothermal process developed in this work could be useful for the construction of many other high-capacity metal sulfide composites as electrode materials for sodium ion batteries

Inorganic Ligand Thiosulfate-Capped Quantum Dots for Efficient Quantum Dot Sensitized Solar Cells

The insulating nature of organic ligands containing long hydrocarbon tails brings forward serious limitations for presynthesized quantum dots (QDs) in photovoltaic applications. Replacing the initial organic hydrocarbon chain ligands with simple, cheap, and small inorganic ligands is regarded as an efficient strategy for improving the performance of the resulting photovoltaic devices. Herein, thiosulfate (S₂O₃^2–), and sulfide (S^2–) were employed as ligand-exchange reagents to get access to the inorganic ligand S₂O₃^2–- and S^2–-capped CdSe QDs. The obtained inorganic ligand-capped QDs, together with the initial oleylamine-capped QDs, were used as light-absorbing materials in the construction of quantum dot sensitized solar cells (QDSCs). Photovoltaic results indicate that thiosulfate-capped QDs give excellent power conversion efficiency (PCE) of 6.11% under the illumination of full one sun, which is remarkably higher than those of sulfide- (3.36%) and OAm-capped QDs (0.84%) and is comparable to the state-of-the-art value based on mercaptocarboxylic acid capped QDs. Photoluminescence (PL) decay characterization demonstrates that thiosulfate-based QDSCs have a much-faster electron injection rate from QD to TiO₂ substrate in comparison with those of sulfide- and OAm-based QDSCs. Electrochemical impedance spectroscopy (EIS) results indicate that higher charge-recombination resistance between potoanode and eletrolyte interfaces were observed in the thiosulfate-based cells. To the best of our knowledge, this is the first application of thiosulfate-capped QDs in the fabrication of efficient QDSCs. This will lend a new perspective to boosting the performance of QDSCs furthermore

Solar Paint from TiO₂ Particles Supported Quantum Dots for Photoanodes in Quantum Dot–Sensitized Solar Cells

The preparation of quantum dot (QD)–sensitized photoanodes, especially the deposition of QDs on TiO₂ matrix, is usually a time-extensive and performance-determinant step in the construction of QD-sensitized solar cells (QDSCs). Herein, a transformative approach for immobilizing QD on the TiO₂ matrix was developed by simply mixing the as-prepared oil-soluble QDs with TiO₂ P25 particles suspension for a period as short as half a minute. The solar paint was prepared by adding the TiO₂/QD composite in a binder solution under ultrasonication. The QD-sensitized photoanodes were then obtained by simply brushing the solar paint on a fluorine-doped tin oxide substrate followed by a low-temperature annealing at ambient atmosphere. Sandwich-structured complete QDSCs were assembled with the use of Cu₂S/brass as counter electrode and polysulfide redox couple as an electrolyte. The photovoltaic performance of the resulting Zn–Cu–In–Se (ZCISe) QDSCs was evaluated after primary optimization of the QD/TiO₂ ratio as well as the thicknesses of photoanode films. In this proof of concept with a simple solar paint approach for photoanode films, an average power conversion efficiency of 4.13% (<i>J</i>_sc = 11.11 mA/cm², <i>V</i>_oc = 0.590 V, fill factor = 0.631) was obtained under standard irradiation condition. This facile solar paint approach offers a simple and convenient approach for QD-sensitized photoanodes in the construction of QDSCs

Band Engineering in Core/Shell ZnTe/CdSe for Photovoltage and Efficiency Enhancement in Exciplex Quantum Dot Sensitized Solar Cells

Even though previously reported CdTe/CdSe type-II core/shell QD sensitizers possess intrinsic superior optoelectronic properties (such as wide absorption range, fast charge separation, and slow charge recombination) in serving as light absorbers, the efficiency of the resultant solar cell is still limited by the relatively low photovoltage. To further enhance photovoltage and cell efficiency accordingly, ZnTe/CdSe type-II core/shell QDs with much larger conduction band (CB) offset in comparison with that of CdTe/CdSe (1.22 eV vs 0.27 eV) are adopted as sensitizers in the construction of quantum dot sensitized solar cells (QDSCs). The augment of band offset produces an increase of the charge accumulation across the QD/TiO2 interface under illumination and induces stronger dipole effects, therefore bringing forward an upward shift of the TiO2 CB edge after sensitization and resulting in enhancement of the photovoltage of the resultant cell devices. The variation of relative chemical capacitance, Cμ, between ZnTe/CdSe and reference CdTe/CdSe cells extracted from impedance spectroscopy (IS) characterization under dark and illumination conditions clearly demonstrates that, under light irradiation conditions, the sensitization of ZnTe/CdSe QDs upshifts the CB edge of TiO2 by the level of ∼50 mV related to that in the reference cell and results in the enhancement of Voc of the corresponding cell devices. In addition, charge extraction measurements have also confirmed the photovoltage enhancement in the ZnTe/CdSe cell related to reference CdTe/CdSe cell. Furthermore, transient grating (TG) measurements have revealed a faster electron injection rate for the ZnTe/CdSe-based QDSCs in comparison with the CdSe cells. The resultant ZnTe/CdSe QD-based QDSCs exhibit a champion power conversion efficiency of 7.17% and a certified efficiency of 6.82% under AM 1.5G full one sun illumination, which is, as far as we know, one of the highest efficiencies for liquid-junction QDSCs.National Natural Science Foundation of China (Nos. 21421004, 91433106, and 21175043), the Science and Technology Commission of Shanghai Municipality (11JC1403100 and 12NM0504101), the Fundamental Research Funds for the Central Universities in China, the CREST program of Japan Science and Technology Agency (JST), and Grant in Aid for Scientific Research (No. 26286013) from the Ministry of Education, Sports, Science and Technology of the Japanese Government for financial suppor