Search

We report an efficiency enhancement of solution-processed CuIn(S,Se)2 (CISSe) thin film solar cells via in situ incorporation of Al2O3. These films were produced using inks containing CuCl, InCl3, AlNO3 (Al/Al + In: 0.1) and thiourea dissolved in methanol. After spin coating of these solutions in air, samples were subjected to a selenization process. Auger electron spectroscopy depth-profiling analysis showed that Al is evenly distributed throughout the bulk of the film. Transmission electron microscopy revealed that AlNO3 precursor reacted with oxygen to form nanosized amorphous Al2O3 grains located within the bulk and grain boundaries of CISSe, as well as at both the top and bottom interfaces. Power conversion efficiency (PCE) as high as 11.6% (JSC: 35.8 mA cm−2, VOC: 518 mV, FF: 62.2%, no anti-reflection coating) was achieved with Al–CISSe solar cell devices integrated with CdS (chemical bath deposition, thickness: 80 nm) and ZnO/ITO bilayers (sputtered, thickness: 300 nm). The average PCE (10.1%, 〈JSC〉: 34.5 mA cm−2, 〈VOC〉: 491 mV, 〈FF〉: 59.8%) was nearly 4% (absolute) higher than that measured on CISSe baseline cells fabricated from solutions without Al (〈PCE〉 = 6.4%, 〈JSC〉: 32.8 mA cm−2, 〈VOC〉: 410 mV, 〈FF〉: 47.3%). This in situ Al2O3 incorporation is speculated to play a role in the enhancement of the VOC and FF of the devices through passivation of defects in CISSe reducing interface and bulk recombination, as evidenced by a reduced defect density and an increased activation energy of the dominant recombination mechanism from capacitance and temperature-dependent VOC measurements, respectively. [ABSTRACT FROM AUTHOR]

Urea electrolysis is an appealing energy conversion technology to produce hydrogen (H2) and alleviate the problem of urea-rich wastewater treatment concurrently. In particular, electrocatalytic performance can be dramatically enhanced by rationally modulating the surface charge distribution with a well-tuned heterostructure. Herein, a heterostructure is constructed by NiMoO4 nanosheets grown on an interior hollow NiS@Ni3S2 nanorods framework (NiS@Ni3S2/NiMoO4). Density functional theory (DFT) calculations demonstrate that the formed heterojunction structure leads to a tailored surface charge state of NiMoO4, with oxygen as the nucleophilic region and molybdenum as the electrophilic region, which facilitates the decomposition of urea molecules and thus significantly improves hydrogen evolution. As expected, the assembled NiS@Ni3S2/NiMoO4 system substantially expedites urea electrolysis activity with a cell voltage of 1.40 V at 10 mA cm−2, which is 200 mV less than the voltage of an overall water splitting system. [ABSTRACT FROM AUTHOR]

The substantial overpotential of CO2 activation, the complex CO2 reduction pathway, and the competitive H2 evolution reaction (HER) limit the practical applications of CO2-based electrochemical energy conversion and storage technologies due to their low energy efficiency and product selectivity. Here, we proposed a strategy that combines mesopores and redox-active couple to effectively capture CO2 and selectively generate CO product. As an example, we construct a redox-active couple, Zn2+/Zn+, on the low-crystallinity mesoporous ZnGa2O4 electrocatalyst. The mesopores not only help to capture CO2 effectively but also inhibit the H2 evolution. The weak lattice constraint of low crystallinity benefits the formation of a Zn2+/Zn+ redox couple to strongly interact with CO2 molecule for subsequent activation and catalytic conversion, thus effectively decreasing the activation energy of CO2 to the active species CO2− and accelerating the proton transfer to form the crucial COOH* intermediate. Consequently, this catalyst exhibited a high faradaic efficiency of 96% among Zn-based electrodes for CO generation at the relatively low applied potential of −1.4 V vs. Ag/AgCl (−0.8 V vs. RHE), and excellent stability during 10 h operation in a 0.1 M KHCO3 solution. [ABSTRACT FROM AUTHOR]

Li-ion and K-ion batteries present their unique advantages of high energy density and low cost, respectively. It is a challenge to explore a universal anode with efficient electrochemical performance. Herein, a two-dimensional TiO2/reduced graphene oxide (RGO) composite was prepared by a facile hydrothermal method. TiO2 nanoparticles are transformed from Ti2C MXene and connect the RGO nanosheets to form a sheet-like structure. Serving as the anode material, the TiO2/RGO presents high capacity, remarkable rate ability and long cycling performance for both Li- and K-ion batteries. The superior electrochemical performance is attributed to the short ion diffusion path due to the small particle size (15–25 nm) and the highway for electron transport provided by RGO. In addition, RGO motivates the capacitive contribution, resulting in enhanced capacity and better rate performance. Meanwhile, the electrochemical kinetics of Li/K-ion storage was investigated by quantitative kinetics analysis. This work demonstrates a possibility to introduce the capacitive capacity to realize rapid ion storage and improve the cycling stability, providing a new strategy to design efficient electrodes for metal-ion batteries. [ABSTRACT FROM AUTHOR]

To balance the electrochemical performance gap between the Li+ insertion/deintercalation anode and the anion adsorption/desorption cathode, in this paper, for the first time, we investigated MnNb2O6 as a new rate capability type anode material for lithium-ion capacitors (LICs). Novel calendula-like MnNb2O6 particles anchored on reduced graphene oxide (rGO) were prepared via a simple two-step hydrothermal route. The special three-dimensional structure and cross-linked conductive network constructed by graphene could shorten the lithium-ion diffusion path, efficiently facilitate electron transmission and adapt to volume strain without shedding during the long-term charge/discharge process. This resulted in excellent charge storage capacity and reasonably superior cycling stability. MnNb2O6@rGO//AC LICs assembled with MnNb2O6@rGO as the cathode and activated carbon (AC) as the anode exhibited excellent performance with maximum energy density of 118 W h kg−1 and power density of 8000 W kg−1 based on the total mass loading of the active material weight. The initial capacity retention was up to 88% after 10 000 charge/discharge cycles, which was higher than that of bimetallic oxide materials reported so far. Therefore, this study might provide a novel rate capability anode material for LICs with high performance. [ABSTRACT FROM AUTHOR]

In this paper, K-doped δ-MnO2 nanoflowers decorated with Au nanoparticles (MnO2–Au) were synthesized by a hydrothermal method. To probe the effect of the band gaps in the MnO2 support over the surface plasmon resonance (SPR)-mediated catalytic conversions on Au nanoparticles (NPs), the oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) was used as a model reaction. We found that the PATP conversion was significantly higher for the MnO2–Au hybrid compared with its individual Au NPs under excitation at 633 nm. Furthermore, the activities of the MnO2–Au materials increased as the MnO2 support displayed higher K-doped levels, which led to narrower band gaps. These results could be explained based on the transfer of photogenerated electrons from MnO2 to Au, increasing the electron density in Au NPs and thus contributing to improved SPR-mediated activity. In this case, our observations show that tuning the band gaps can have a significant impact on SPR-mediated conversions, in which narrower band gaps should facilitate the charge transfer of SPR-excited charge carriers and thus lead to better performances. Our findings presented may provide important insights into the role of the support materials in plasmonic catalysis, indicating that, in addition to the control over several physical and chemical parameters (such as shape, surface area, defects, among others), the proper tuning of the band gap can serve as an effective strategy for the optimization of activities. [ABSTRACT FROM AUTHOR]

A novel strategy was used to prepare a high performance micro-porous polymer electrolyte (MPE) from a poly(arylene ether ketone) (PAEK)/poly(ethylene glycol) grafted poly(arylene ether ketone) (PAEK-g-PEG) polymer composite membrane matrix incorporating a chitosan based LiClO4 gel electrolyte. The morphology, porosity, and thermal and mechanical properties of the PAEK/PAEK-g-PEG polymer blend membrane matrix were investigated. To improve the liquid retention capacity of the MPE, a simple but effective method involving the addition of chitosan was implemented. The effects of chitosan concentration on the liquid uptake and leakage behaviors as well as the ionic conductivity of the electrolyte were also evaluated. The synthesized MPE exhibited an ionic conductivity as high as 8 × 10−3 S cm−1 at room temperature. More importantly, a novel solid-state electric double layer capacitor (S-EDLC) could be fabricated using the synthesized MPE and activated carbon electrodes. For comparison, an EDLC was also assembled using the corresponding aqueous electrolyte and a commercial separator (NKK-MPF30AC-100). Alternating current (AC) impedance measurement results showed that the interfacial compatibility of the MPE and the activated carbon electrodes was high. Meanwhile, the as-prepared S-EDLC showed a specific capacitance of 118.63 F g−1, with an energy density of 7.87 W h kg−1 and power density being 95.97 W kg−1 at a current density of 1 A g−1. Furthermore, the S-EDLC exhibited greater cell-cycling stability after 5000 charge/discharge cycles than did the EDLC, indicating that this novel MPE should be suitable for use in EDLCs and other energy storage systems. [ABSTRACT FROM AUTHOR]

Lithium–sulphur batteries have attracted increasing interest due to their high theoretical specific capacity, advantageous economy, and environmental friendliness. With migration of soluble lithium polysulfide (Li2Sn, 4 ＜ n≤ 8) in mind, we prepared one novel Zn(ii) metal–organic framework (MOF) based separator for lithium–sulphur batteries. It is able to play an efficient role as an ionic sieve for the soluble polysulfide ions. More importantly, the battery with Zn(ii)–MOF based separator exhibited much lower capacity decay of 0.041% per cycle at 1C over 1000 cycles. [ABSTRACT FROM AUTHOR]

In a mesoporous hybrid perovskite solar cell (PSC), the mesoporous scaffold plays key roles in controlling the crystallization of the perovskite material and in the charge carrier transport, and hence is critical for developing highly efficient PSCs. Here we report a study on blending micrometer-long TiO2 nanorods (NRs) into the commonly used nanoparticles (NPs) to optimize the mesoporous structure, with the aim of enhancing the perovskite material loading and connectivity as well as light harvesting. It was found that with 5–10% of NR incorporation, a uniform scaffold can be spin-coated and the PSC performance was improved. In comparison to the pure NP-based device, the power conversion efficiency was increased by about 27% when 10% of the NRs were incorporated, due to enhanced light harvesting and charge collection. However, with more NR blending, a homogeneous scaffold cannot be formed, resulting in PSC performance degradation. These findings contribute to a better design of mesoporous scaffolds for high-performance PSCs. [ABSTRACT FROM AUTHOR]

CH3NH3PbI3 (MAPbI3) perovskite thin films that are solution-processed using either a one-step or two-step conventional method typically contain a significant number of defects (voids, pinholes) or PbI2 impurities, which have a detrimental effect on the performance of planar perovskite solar cells (PSCs) fabricated using those films. To overcome this issue, we show that enhancement of the solid-state reaction between inorganic–organic precursors is an effective route for the growth of compact, phase-pure MAPbI3 perovskite thin films with no voids or pinholes. To ensure uniform solid-state conversion (MAI + PbI2→ MAPbI3) across the entire film thickness, a new successive spin coating/annealing (SSCA) process is used, where MAI is repeatedly infiltrated into a nanoporous PbI2 film, followed by thermal annealing. The mechanisms involved in the SSCA process are elucidated by monitoring the evolution of the phases during the reaction. Owing to these desirable characteristics (high-purity, full-coverage, enhanced smoothness and compactness) of the SSCA MAPbI3 films, planar PSCs based on these perovskite thin films delivered a maximum power conversion efficiency (PCE) close to 15%. Furthermore, PSCs fabricated using partially converted nanoporous PbI2 thin films delivered a surprising PCE approaching 10%, suggesting continuous MAPbI3 phase formation throughout the entire film at each spin coating/annealing process. The advantages gained from enhancing the solid-state precursor reactions allow better control of the growth of the perovskite making the SSCA process more robust. [ABSTRACT FROM AUTHOR]

We demonstrate a three-step sequential solution process to prepare PbI2-free CH3NH3PbI3 perovskite films. In this three-step method, a thermally unstable stoichiometric PbI2·CH3NH3Cl precursor film is first deposited on the mesoporous TiO2 substrate, followed by thermal decomposition to form PbI2, which is finally converted into CH3NH3PbI3 by dipping in a regular isopropanol solution of CH3NH3I at room temperature. In comparison to the two-step approach using similar processing conditions, the three-step method enables the formation of the PbI2 film through the thermal decomposition of the PbI2·CH3NH3Cl precursor film. This facilitates a rapid conversion of PbI2 to CH3NH3PbI3 without any traceable residue PbI2 in the final conversion step, leading to an improved device performance. [ABSTRACT FROM AUTHOR]

Three 9,9-dihexyl-9H-fluorene (DHF) functionalized zinc porphyrin dyes (coded as ZZX-N3, ZZX-N4, and ZZX-N5) were designed and synthesized for dye-sensitized solar cells. Then, DHF and benzoic acid were conjugated to the porphyrin ring through triple bonds to act as a spacer to elongate the π-conjugation and as an acceptor for an efficient electron injection, respectively. A bis(9,9-dihexyl-9H-fluorene-7-yl)-amine (BFA) and a bis(4-hexylphenyl)amine (BPA) were further linked to DHF to act as electron donors in ZZX-N3 and ZZX-N4, respectively. ZZX-N5 did not have any electron donor and served as a reference. Moreover, ZZX-N3- and ZZX-N4-sensitized cells exhibited broader sunlight absorption than ZZX-N5, and as a result, higher photon-to-electricity efficiency (PCE) (ZZX-N3, 3.83%; ZZX-N4, 4.2%; ZZX-N5, 3.70%) was observed. The results are consistent with well-separated HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) in ZZX-N3 and ZZX-N4 than in ZZX-N5. However, the overall conversion efficiency of ZZX-N3- and ZZX-N4-sensitized cells was low, which is due to significant dye aggregation induced by the extra long alkyl-chains on the donor groups. This was evidenced by blue and red shifts of the absorption spectra of dye-coated TiO2 films. In addition, the extra long-chains also did not offer better shielding to prevent electron recombination of injected electrons with I3- in electrolyte as revealed by electrochemical impedance spectroscopy. When a co-sensitizer (coded as PBS) was used, a new peak corresponding to the absorption of PBS at 560 nm was observed on the incident photon to charge carrier efficiency (IPCE) spectra; however, the overall photovoltaic performance was not improved due to the significant decrease of dye-loading density of porphyrin dyes, indicating a need to break off the trade-off between dye-loading and light-harvesting. [ABSTRACT FROM AUTHOR]

Vertically oriented graphene (VOG), with graphene sheets perpendicular to the substrate, exhibits meritorious electrocatalytic properties due to the fully exposed graphene (or graphitic) edges and other plasma introduced defects, even without any heteroatom functionalization. We report the growth and electrocatalytic properties of VOG by plasma-enhanced chemical vapor deposition using methane and nitrogen as source gases. Nitrogen was adopted as plasma ancillary gas to obtain a higher plasma temperature that promotes VOG growth with better electrocatalytic performance, as comparative studies demonstrated. Electron transfer dynamics measurement using a Fe(CN)63-/4- redox couple found reduction and oxidation peak-to-peak separation as low as 70 mV, indicating rapid electron-transfer kinetics. The electrocatalytic activity of the VOG electrode on an I-/I3- redox couple was found approaching that of platinum. Using VOG as the counter electrode for dye-sensitized solar cells (DSSCs), a promising power conversion efficiency of 7.63% was demonstrated. Electrochemical impedance spectroscopic study further discloses the impact of VOG properties on DSSC performance. [ABSTRACT FROM AUTHOR]