A dual strategy of Na+/vacancy disorder and high Na to construct a P2-type cathode for high-stability sodium-ion batteries.

P2-type layered oxides are widely regarded as highly promising contenders for cathode materials in sodium-ion batteries. However, the occurrence of severe reactive phase transitions hinders satisfactory cycling stability and rate performance, thereby imposing limitations on their practical application. Here we prepared P2-type Na0.75Ni0.23Mg0.1Mn0.67O2 cathode materials using the agar gel approach. The use of agar reduces the synthesis time significantly, and the high Na content enhances the stability of the structure and contributes to its capacity. Meanwhile, the introduction of electrochemically inactive Mg ions into sodium layers not only disrupts the Na+/vacancy ordering, but also increases the spacing between sodium layers, thus reducing the diffusion barrier for sodium ions. The dual modification strategy led to excellent stability of Na0.75Ni0.23Mg0.1Mn0.67O2 with 94% capacity retention after 100 cycles at 1C. This work provides new insights into the design of sodium-ion cathode materials.

Electrochemical production of hydrogen peroxide by non-noble metal-doped g-C3N4 under a neutral electrolyte.

Electrochemical oxygen reduction (ORR) for the production of clean hydrogen peroxide (H2O2) is an effective alternative to industrial anthraquinone methods. The development of highly active, stable, and 2e- ORR oxygen reduction electrocatalysts while suppressing the competing 4e- ORR pathway is currently the main challenge. Herein, bimetallic doping was successfully achieved based on graphitic carbon nitride (g-C3N4) with the simultaneous introduction of K and Co, whereby 2D porous K-Co/CNNs nanosheets were obtained. The introduction of Co promoted the selectivity for H2O2, while the introduction of K not only promoted the formation of 2D nanosheets of g-C3N4, but also inhibited the ablation of H2O2 by K-Co/CNNs. Electrochemical studies showed that the selectivity of H2O2 in K-Co/CNNs under neutral electrolyte was as high as 97%. After 24 h, the H2O2 accumulation of K-Co/CNNs was as high as 31.7 g L-1. K-Co/CNNs improved the stability of H2O2 by inhibiting the ablation of H2O2, making it a good 2e- ORR catalyst and providing a new research idea for the subsequent preparation of H2O2.

Mn2+-Doped MoS2/MXene Heterostructure Composites as Cathodes for Aqueous Zinc-Ion Batteries.

Typical layered transition-metal chalcogenide materials, especially MoS2, are gradually attracting widespread attention as aqueous Zn-ion battery (AZIB) cathode materials by virtue of their two-dimensional structure, tunable band gap, and abundant edges. The metastable phase 1T-MoS2 exhibits better electrical conductivity, electrochemical activity, and zinc storage capacity compared to the thermodynamically stable 2H-MoS2. However, 1T-MoS2 is still limited by the phase stability and layered structure destruction for AZIB application. Thus, a three-dimensional interconnected network heterostructure (Mn-MoS2/MXene) consisting of Mn2+-doped MoS2 and MXene with a high percentage of 1T phase (82.9%) was synthesized by hydrothermal methods and investigated as the cathode for AZIBs. It was found that S-Mn-S covalent bonds between MoS2 interlayers and Ti-O-Mo bonds at heterogeneous interfaces can act as "electron bridges" to facilitate electron and charge transfer. And the doping of Mn2+ and the combination of MXene not only expanded the interlayer spacing of MoS2 but also maintained the metastable structure of 1T-MoS2 nanosheets, acting to reduce the activation energy for Zn2+ intercalation and enhance specific capacity. The obtained Mn-MoS2/MXene contains more 1T-MoS2 and provides an improved specific capacity of 191.7 mAh g-1 at 0.1 A g-1. Compared with Mn-MoS2 and pure MoS2, it also exhibits enhanced cycling stability with a capacity retention of 80.3% after 500 cycles at 1 A g-1. Besides, the conductivity of Mn-MoS2/MXene is significantly improved, which induces a lower activation energy of the zinc ions during intercalation/deintercalation.

Highly Reversible Lithium-Ion Battery with Excellent Rate Performance and Cycle Stability Based on a Ti3C2/CoS2 Composite Anode.

Transition metal sulfide (TMS) CoS2 is considered an ideal anode material for new-generation lithium-ion batteries (LIBs) because of its high specific capacity, high electrochemical activity, and low cost. However, CoS2 is prone to volume expansion and structural collapse when it participates in the internal conversion reaction of the battery, which limits its practical application. After analyzing the failure mechanism of CoS2 as the anode material of LIBs, the concept of nanoengineered materials is introduced here. CoS2 particles are nanosized and stabilized by constructing a composite structure on an alkali-treated two-dimensional Ti3C2 Mxene conductive network. Both experiments and theoretical calculations show that special Ti-O-Co bonds are formed at the interface of the Ti3C2/CoS2 composite through oxygen-containing functional groups. Ti-O-Co bonding with adjustable electronic characteristics can effectively promote the utilization rate of anode materials, electronic conductivity, and ionic diffusivity and thus enhance the redox reaction kinetics of the device. When the Ti3C2/CoS2 composite is used as the anode material for LIBs, it still provides a high specific capacity of 405.8 mAh g-1 after 100 cycles at 0.1 A g-1. After running for 1000 cycles at a high current of 1 A g-1, the capacity retention is still close to 100%. Also, high cycle stability under the condition of highly active material loading (10.58 mg cm-2) and low electrolyte/active material ratio (10 µL mg-1) is achieved. This work provides a new idea for the development of commercial LIBs as anode materials.

Transition metal single atom-optimized g-C3N4 for the highly selective electrosynthesis of H2O2 under neutral electrolytes.

Neutral electrosynthesis of H2O2via the 2e- ORR is attractive for numerous applications, but the low activity and high cost of electrocatalysts have become important constraints. Therefore, the development of cheap and efficient electrocatalysts for the 2e- ORR is necessary. Herein, we report the embedding of transition metal single atoms (TM SAs) in g-C3N4 nanosheets (CNNS). The introduction of TM SAs increases the N-CN content and reduces the C-C/CC content in CNNS, which contributes to the increased selectivity of TM SA/CNNS for the 2e- ORR. TM SA is the main reason for the enhanced activity of the 2e- ORR. Based on the results obtained by replacing a series of TM SA, the Ni0.10 SA/CNNS with optimal N-CN content exhibited the best selectivity (∼98%) and highest yield of H2O2 (∼503 mmol gcat-1 h-1), which is ∼14.6 times higher than that of CNNS (∼34.4 mmol gcat-1 h-1). Other TM SA/CNNS also exhibited high activity and selectivity. This study demonstrates the ability of TM SA to modulate the selectivity and activity of CNNS, making it a promising candidate for the 2e- ORR and providing more reference ideas for the preparation of H2O2.

Photoassisted Electrochemical Hydrogen Evolution Reaction of MFe2O4@Ultrathin Black Phosphorus Amorphous-Crystalline Interface.

Exploring highly active, stable, and low-cost catalysts for photoelectrochemical hydrogen evolution reaction (PE-HER) is vital in the field of energy conversion. Herein, we construct a new amorphous crystalline interface that amorphous iron-based spinel oxide (A-MFe2O4 (M = Ni, Co, Zn)) is uniformly anchored on the crystalline exfoliated black phosphorus (C-EBP) nanosheets via electrochemical and solvothermal strategies. Among these A-MFe2O4@C-EBP catalysts, more oxygen defects of A-NiFe2O4@C-EBP interface provide a larger effective electrochemical active area of 32.33 mF cm-2 as well as a turnover frequency of 0.44 s-1 and allow for an optimum equilibrium of the hydrogen-containing adsorption intermediates. Furthermore, A-NiFe2O4@C-EBP exhibits significant PE-HER performance with an overpotential of 42 mV at 10 mA cm-2 under visible-light irradiation. Density functional theory (DFT) calculations show that the amorphous-crystalline composite structure causes a large number of oxygen defects enhancing the intrinsic activity of A-NiFe2O4@C-EBP, which A-NiFe2O4@C-EBP significantly improves its adsorption capacity for H* for HER and has the lowest Gibbs free energy change for HER. This study not only provides a superior multifunctional amorphous-crystalline interface catalysts but also helps to understand the catalytic mechanism of PE-HER.

Multi-Dimensional Composite Frame as Bifunctional Catalytic Medium for Ultra-Fast Charging Lithium-Sulfur Battery.

The shuttle effect of soluble lithium polysulfides (LiPSs) between electrodes and slow reaction kinetics lead to extreme inefficiency and poor high current cycling stability, which limits the commercial application of Li-S batteries. Herein, the multi-dimensional composite frame has been proposed as the modified separator (MCCoS/PP) of Li-S battery, which is composed of CoS2 nanoparticles on alkali-treated MXene nanosheets and carbon nanotubes. Both experiments and theoretical calculations show that bifunctional catalytic activity can be achieved on the MCCoS/PP separator. It can not only promote the liquid-solid conversion in the reduction process, but also accelerate the decomposition of insoluble Li2S in the oxidation process. In addition, LiPSs shuttle effect has been inhibited without a decrease in lithium-ion transference numbers. Simultaneously, the MCCoS/PP separator with good LiPSs adsorption capability arouses redistribution and fixing of active substances, which is also beneficial to the rate performance and cycling stability. The Li-S batteries with the MCCoS/PP separator have a specific capacity of 368.6 mAh g-1 at 20C, and the capacity decay per cycle is only 0.033% in 1000 cycles at 7C. Also, high area capacity (6.34 mAh cm-2) with a high sulfur loading (7.7 mg cm-2) and a low electrolyte/sulfur ratio (7.5 µL mg-1) is achieved.

Self-Supporting Multicomponent Hierarchical Network Aerogel as Sulfur Anchoring-Catalytic Medium for Highly Stable Lithium-Sulfur Battery.

The low utilization rate of active materials, shuttle effect of lithium polysulfides (LiPSs), and slow reaction kinetics lead to the extremely low efficiency and poor high current cycle stability of lithium sulfur batteries (Li-S batteries). In this paper, a self-supporting multicomponent hierarchical network aerogel is proposed as the modified cathode (S/GO@MX@VS4 ). It consists of graphene (GO) and MXene nanosheets (MX) loaded with VS4 nanoparticles. The experimental results and first-principles calculations show that the GO@MX@VS4 aerogel has strong adsorption and reversible conversion effects on LiPSs. It can not only inhibit the shuttle effect and improve the utilization rate of active substances by keeping the chain crystal structure of VS4 , but also promote the reversibility and kinetics of the reaction by accelerating the liquid-solid transformation in the reduction process and the decomposition of insoluble Li2 S in the oxidation process. The GO@MX@VS4 aerogel modified cathode with a multicomponent synergy exhibits the capacity ratios (Q1 /Q2 ) at different discharge stages is close to the theoretical value (1:2.8), and the capacity decay per cycle is 0.019% in 1200 cycles at 5C. Also, a high areal capacity of 6.90 mAh cm-2 is provided even at high sulfur loading (7.39 mg cm-2 ) and low electrolyte/sulfur ratio (E/S, 8.0 µL mg-1 ).

Construction Strategy of VO2@V2C 1D/2D Heterostructure and Improvement of Zinc-Ion Diffusion Ability in VO2 (B).

VO2 (B) electrode material has relatively high capacity and good cycle stability. However, its poor rate performance limits its further development because of the strong interaction between zinc ions and the main lattice of VO2 (B). Herein, considering the design principle of rate performance improvement, we furnished a different scheme from a previous multistep method of the synthesis-modification strategy of pure VO2 (B). VO2@V2C 1D/2D heterostructure was constructed by controllable partial oxidation of V2C by a one-step hydrothermal method. The unique 1D/2D heterostructure improves diffusivity and reduces the diffusion size of zinc ions at the same time, which significantly improved the rate performance of VO2. The situation at the heterostructure interface is analyzed by Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. Combined with cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent title technology tests, the promotion mechanism for the rate performance of the derived VO2 is further explained. In addition, it is found that V2C MXene can be electrochemically activated when the voltage reaches 1.24 V. By further widening the voltage window to activate V2C, VO2@V2COx heterostructure was obtained, which realizes high capacity and maintains high rate performance in aqueous zinc-ion batteries. This work provides key insights for the design of high-rate-performance electrode materials for aqueous zinc-ion batteries.

Dual Functional Dopant-Free Contacts with Titanium Protecting Layer: Boosting Stability while Balancing Electron Transport and Recombination Losses.

Combining electron- and hole-selective materials in one crystalline silicon (Si) solar cell, thereby avoiding any dopants, is not considered for application to photovoltaic industry until only comparable efficiency and stable performance are achievable. Here, it is demonstrated how a conventionally unstable electron-selective contact (ESC) is optimized with huge boost in stability as well as improved electron transport. With the introduction of a Ti thin film between a-Si:H(i)/LiF and Al electrode, high-level passivation (Seff  = 4.6 cm s-1 ) from a-Si:H(i) and preferential band alignment (ρC  = 7.9 mΩ cm2 ) from low work function stack of LiF/Ti/Al are both stably retained in the newly constructed n-Si/a-Si:H(i)/LiF/Ti/Al ESC. A detailed interfacial elements analysis reveals that the efficiently blocked inward diffusion of Al from electrode by the Ti protecting layer balances transport and recombination losses in general. This excellent electron-selective properties in combination with large process tolerance that enable remarkable device performance, particularly high efficiencies of 22.12% and 23.61%, respectively, are successfully approached by heterojunction solar cells with dopant-free ESC and dopant-free contacts for both polarities.

Sulfur-Bridged Bonds Boost the Conversion Reaction of the Flexible Self-Supporting MnS@MXene@CNF Anode for High-Rate and Long-Life Lithium-Ion Batteries.

Manganese sulfide (MnS) has been found to be a suitable electrode material for lithium-ion batteries (LIBs) owing to its considerable theoretical capacity, high electrochemical activity, and low discharge voltage platform, while its poor electrical conductivity and severe pulverization caused by volume expansion of the material limit its practical application. To improve the rate performance and cycle stability of MnS in LIBs, the structure-control strategy has been used to design and fabricate new anode materials. Herein, the MnS@MXene@CNF (MMC, CNFs means carbon nanofibers) electrode has been prepared by electrospinning and a subsequent high-temperature annealing process. The MMC electrode exhibits excellent cyclic stability with a capacity retention rate close to 100% after 1000 cycles at 1000 mA/g and an improved rate performance with a specific capacity up to 500 mAh/g at a high current density of 5000 mA/g, much higher than the 308 mAh/g of the MnS@CNF (MC) electrode. The elevated electrochemical performance of the MMC electrode not only benefits from the unique structure of MnS nanoparticles evenly dispersed in the well-designed flexible self-supporting three-dimensional (3D) CNF network but, more importantly, also benefits from the formation of sulfur-bridged Mn-S-C bonds at the MnS/MXene interface. The newly formed bonds between MnS and MXene nanosheets can stabilize the structure of MnS near the interfaces and provide a channel for fast charge transfer, which notably increase both the reversibility and the rate of the conversion reaction during the charge/discharge process. This work may pave a new path for designing stable and self-supporting anodes for high-performance LIBs.

Interlayer Modification of Pseudocapacitive Vanadium Oxide and Zn(H2 O)n 2+ Migration Regulation for Ultrahigh Rate and Durable Aqueous Zinc-Ion Batteries.

The interlayer modification and the intercalation pseudocapacitance have been combined in vanadium oxide electrode for aqueous zinc-ion batteries. Intercalation pseudocapacitive hydrated vanadium oxide Mn1.4 V10 O24 ·12H2 O with defective crystal structure, interlayer water, and large interlayer distance has been prepared by a spontaneous chemical synthesis method. The inserted Mn2+ forms coordination bonds with the oxygen of the host material and strengthens the interaction between the layers, preventing damage to the structure. Combined with the experimental data and DFT calculation, it is found that Mn2+ refines the structure stability, adjusts the electronic structure, and improves the conductivity of hydrated vanadium oxide. Also, Mn2+ changes the migration path of Zn2+ , reduces the migration barrier, and improves the rate performance. Therefore, Mn2+ -inserted hydrated vanadium oxide electrode delivers a high specific capacity of 456 mAh g-1 at 0.2 A g-1 , 173 mAh g-1 at 40 A g-1 , and a capacity retention of 80% over 5000 cycles at 10 A g-1 . Furthermore, based on the calculated zinc ion mobility coefficient and Zn(H2 O)n 2+ diffusion energy barrier, the possible migration behavior of Zn(H2 O)n 2+ in vanadium oxide electrode has also been speculated, which will provide a new reference for understanding the migration behavior of hydrated zinc-ion.

Improved CdS photocatalytic H2 evolution using Au-Ag nanoparticles with tunable plasmon-enhanced resonance energy transfer.

Plasmon-mediated photocatalytic systems often suffer from weak absorption spectra overlap which limits energy transfer between plasmon metals and semiconductors. Herein, Au-Agx@CdS90 nanoparticles (NPs) with adjustable spectral overlap were prepared. Au-Ag hollow nanoparticles (HNPs) with tunable plasmon absorption peaks were used as the template and were coated with CdS to achieve stepwise spectral overlap for enhanced energy transfer. As the spectral overlap increased between Au-Ag HNPs and CdS, the H2 evolution rate increased and then decreased. Under visible-light irradiation, Au-Ag487@CdS90 nanoparticles (NPs) delivered an H2 evolution rate of 18.73 mmol h-1 g-1, which was 2.2 times higher than pure CdS. The plasmon resonance energy transfer from Au-Ag HNPs to the CdS semiconductor increased the generation of charge carriers in the semiconductor and enhanced the photocatalytic performance. By regulating the position of the plasmon absorption peaks of the noble metal nanoparticles, changing the spectral overlap between metal and semiconductor to enhance the PRET effect is beneficial to the design of new plasmon photocatalysts.

Synthesis of Co2-xNixO2 (0 < x < 1.0) hexagonal nanostructures as efficient bifunctional electrocatalysts for overall water splitting.

Designing low-cost and high-performance bifunctional electrocatalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is vitally important for water splitting. Herein, we synthesize Co2-xNixO2 (0 < x < 1.0) hexagonal nanosheets with different Co/Ni molar ratios via a facile coprecipitation process followed by calcination under an Ar atmosphere. Changing the Co/Ni molar ratios of the Co2-xNixO2 products is found to have a momentous influence on the microstructures, specific surface areas and electrocatalytic performances. At a Co/Ni molar ratio of 0.6, the Co1.4Ni0.6O2 nanosheet exhibits the largest specific surface area of 60.63 m2 g-1, the best OER with an onset overpotential of 278.5 mV, and HER of 72.8 mV as a bifunctional electrocatalyst. Meanwhile, the minimum Tafel slope is 113.6 mV dec-1 for OER and 77.4 mV dec-1 for HER. The Co1.4Ni0.6O2 nanosheet has excellent OER and HER activity at 0.1 mg cm-2 trace loading. Moreover, we construct an overall water splitting cell using the Co1.4Ni0.6O2 bifunctional electrocatalyst in a two-electrode system to further demonstrate the practical application, which needs a cell voltage of 1.75 V at a current density of 10 mA cm-2 and exhibits great long-term stability. These results provide an efficient strategy for the rational design of Co-based oxides towards bifunctional overall water electrocatalysts.

Bifunctional catalysts of CoNi nanoparticle-embedded nitrogen-doped carbon nanotubes for rechargeable Zn-air batteries.

It is essentially important to improve the performance of Zn-air batteries by studying bifunctional catalysts for oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) with low-cost, high-efficiency and high-stability properties. Here, CoNi nanoparticles embedded in the bamboo-like N-doped carbon tubes (Co x Ni y @NC) were synthesized, where the optimized catalyst of Co2Ni1@NC exhibits superior bifunctional electrocatalytic activity, showing a low overpotential of 300 mV under the current density of 10 mA cm-2 for OER and a large limiting current density of 3.76 mA cm-2 under 0.40 V for ORR in an alkaline solution. In addition, the Co2Ni1@NC also shows excellent electrocatalytic activity in acidic and neutral solutions. Importantly, primary Zn-air batteries based on Co2Ni1@NC affords an excellent specific capacity of 834 mAh/gZn with a discharge potential of 1.25 V at 5 mA cm-2. A rechargeable Zn-air battery assembled with Co2Ni1@NC shows excellent cycling stability, where the first discharge and charge voltages reach 1.21 and 2.00 V under 1 mA cm-2, respectively. This finding provides a simple synthesis approach, which allows one to construct bifunctional catalysts based on metal@NC for future energy conversion and storage devices.

Multilevel Static-Dynamic Anticounterfeiting Based on Stimuli-Responsive Luminescence in a Niobate Structure.

Anticounterfeiting is a highly required technique to protect the product and the consumer rights in the modern society. The conventional luminescent anticounterfeiting is based on downconversion luminescence excited by an ultraviolet light, which is easy to be faked. In this work, we realized six luminescent modes in a niobate-based structure (LiNbO3:RE3+, RE3+ = Pr3+, Tm3+, Er3+, Yb3+), in which photostimulated luminescence of LiNbO3:Pr3+, and upconversion luminescence color evolution of LiNbO3:Er3+ were first presented. Based on the above luminescent modes of LiNbO3:RE3+, multilevel anticounterfeiting devices were developed. By employing mechanoluminescence and persistent luminescence, we achieved dual-mode anticounterfeiting that could display the luminescent patterns without any direct irradiation. In addition, another dual-mode anticounterfeiting based on photostimulated luminescence and upconversion luminescence excited by a near-infrared light was realized, which could display the anticounterfeiting patterns in both static and dynamic states. To obtain an even higher anticounterfeiting level, downconversion luminescence, thermoluminescence, photostimulated luminescence, and upconversion luminescence were simultaneously applied in a food trademark. This four-mode anticounterfeiting trademark could not only show a static-dynamic luminescence that is hard to be faked but also allow consumers to distinguish the food freshness. The presented multilevel anticounterfeiting strategies could be employed to resolve the counterfeit issues in various fields.

Carbon fabric supported 3D cobalt oxides/hydroxide nanosheet network as cathode for flexible all-solid-state asymmetric supercapacitor.

Owing to a lack of electroactive sites and poor conductivity, Co oxides/hydroxides nanosheet network electrodes usually show low experimental capacity, hardly meeting the demand for high energy density needed for an asymmetric supercapacitor. Herein, we demonstrate a surface capacity enhancement of a 3D cobalt oxides/hydroxides nanosheet network cathode through a simple cyclic voltammetry electro-deposition method. By optimizing the electro-deposition parameters, the as-prepared Co oxides/hydroxides nanosheet network electrode delivers a significantly high capacity of 427 C g-1 at the current density of 1 A g-1 and excellent rate ability of 79.8% at the current density of 10 A g-1, as well as outstanding cycling life. A detailed voltammetric analysis using the power-law relationship and Trasatti's method shows that both the large surface area, high pore volume and polycrystalline nature contribute to the enhancement of the surface capacity. In addition, the assembled asymmetric all-solid-state supercapacitor also presents a volume energy density of 2.78 mW h cm-3 at a power density of 14 mW cm-3 and excellent cycling stability. In addition, our prepared asymmetric supercapacitor shows super flexibility and was used to light up a heart-shaped logo. This work may provide valuable insights into the design and fabrication of electrode materials with improved capacity and rate ability.

Nitrogen and Sulfur Self-Doped Activated Carbon Directly Derived from Elm Flower for High-Performance Supercapacitors.

N,S-Doped activated carbon was directly prepared via a facile and cost-efficient hydrothermal reaction, followed by alkali activation of elm flower (EL)-derived biomass. The EL-derived activated carbon (ELAC) had N and S contents of 2.21 and 6.06 atom %, respectively, in addition to a high Brunauer-Emmett-Teller (BET) surface area of 2048.6 m2 g-1 and moderate pore volume of 0.88 cm3 g-1. Owing to its high BET surface area and N/S functional groups, ELAC achieved a specific capacitance of 275 F g-1 at a current density of 1 A g-1 and retained a capacitance of 216 F g-1 at 20 A g-1. In addition, a symmetric supercapacitor based on N,S-self-doped ELAC electrode provided a capacitance of 62 F g-1 at a current density of 10 A g-1, with maximum energy and power densities of 16.8 Wh kg-1 and 600 W kg-1, respectively. The capacitance retention was also high, at 87.2%, at 4 A g-1 after 5000 cycles.

Impacts of Mn ion in ZnSe passivation on electronic band structure for high efficiency CdS/CdSe quantum dot solar cells.

Surface passivation in quantum dot-sensitized solar cells (QDSSCs) plays a very important role in preventing surface charge recombination and thus enhancing the power conversion efficiency (PCE). ZnSe passivation with dopant in CdS/CdSe co-sensitized QDSSCs has been demonstrated as an effective way to improve the PCE. In the present study, a series of characterizations revealed that a Mn-doped ZnSe passivation layer can not only reduce surface charge recombination, but also enhance light harvesting. By means of density functional theory calculation along with a systematic study of electronic band structure, it has been found that the valence band of ZnSe moves upward on Mn-ion doping which leads to acceleration of charge separation and broader light absorption range. The impact of the Mn ion on charge recombination and light harvesting has been interpreted reasonably and the PCE of CdS/CdSe co-sensitized QDSSCs with Mn-doped ZnSe passivation layer is as high as 6.46%, which is 1.5 times that of the solar cell without the passivation layer.

Charge recombination control for high efficiency CdS/CdSe quantum dot co-sensitized solar cells with multi-ZnS layers.

ZnS as an inorganic passivation agent has been proven to be effective in suppressing charge recombination and enhancing power conversion efficiency (PCE) in quantum dot-sensitized solar cells (QDSCs). In the present study, we constructed a novel TiO2/ZnS/CdS/ZnCdS/CdSe/ZnS photoelectrode via successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD). The complementary effects of multi-ZnS layers on the optical and electrochemical performance of the QDSCs were systematically investigated. The multi-ZnS can not only facilitate the growth and distribution of QDs, but also suppress the different interface charge recombination effectively. We suggest that the formation of the ZnCdS intermediate layers via ion-exchange route during CBD process contributes to the higher photoelectrochemical cell performance of the QDSCs with the middle ZnS layer. When the three-layer ZnS was employed in CdS/CdSe co-sensitized system, the PCE reached 6.05%, which is much higher than that observed for solar cells with the conventional single ZnS treatments and the two layers inserted at the interface between CdS QDs and CdSe QDs and electrolyte (4.80% and 5.42%, respectively).