Two-Dimensional Materials for Highly Efficient and Stable Perovskite Solar Cells

Perovskite solar cells(PSCs)offer low costs and high power conversion efficiency.However,the lack of long-term stability,primarily stemming from the interfacial defects and the sus-ceptible metal electrodes,hinders their practical application.In the past few years,two-dimensional(2D)materials(e.g.,graphene and its derivatives,transitional metal dichalcogenides,MXenes,and black phosphorus)have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces,layer-dependent electronic band structures,tunable functional groups,and inherent compactness.Here,recent progress of 2D material toward efficient and stable PSCs is summarized,including its role as both interface materials and electrodes.We discuss their beneficial effects on perovskite growth,energy level alignment,defect passivation,as well as blocking external stimulus.In particular,the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized.Finally,perspectives on the further development of PSCs using 2D materials are provided,such as designing high-quality van der Waals heterojunction,enhancing the uniformity and coverage of 2D nanosheets,and developing new 2D materials-based electrodes.

An In-Situ Formed Tunneling Layer Enriches the Options of Anode for Efficient and Stable Regular Perovskite Solar Cells

Perovskite solar cells(PSCs)are taking steps to commercialization.However,the halogen-reactive anode with high cost becomes a stumbling block.Here,the halogen migration in PSCs is utilized to in situ generate a uniform tunneling layer between the hole transport materials and anodes,which enriches the options of anodes by breaking the Schottky barrier,enabling the regular PSCs with both high efficiency and stability.Specifically,the regular PSC that uses silver iodide as the tunneling layer and copper as the anode obtains a champion power conversion efficiency of 23.24%(certified 22.74%)with an aperture area of 1.04 cm^(2).The devices are stable,maintaining 98.6%of the initial effi-ciency after 500 h of operation at the maximum power point with continuous 1 sun illumination.PSCs with different tunneling layers and anodes are fabricated,which confirm the generality of the strategy.

Ni-P-Nanodiamond composite electroless plating

The effect of nanodiamond content in electrolyte and rotational speed of the stirrer on the deposition rate of coatings, the nanodiamond content in coatings, the micro- structure and the micro-hardness of coatings were studicd. A self-made pin-on-disk tribo-meter was employed to evaluate the wear resistance of prepared coatings. Re- sults show that the thickness of composite coating decreases with the rotational speed, while the micro hardness of coating and the content of nanodiamond in coating increase with increasing its content in electrolyte. The wear resistance of the composite coating deposited in an electrolye with 6 g/L nanodiamond increases by 50% in contrast with the pure Ni-P coating.

Preparation of FeCo-, FeNi- and NiCo-alloy coated cenosphere composites by heterogeneous precipitation

Precursors of binary alloy （Fe112C0112, Fel/2Ni1/2, Ni1/2Co1/2, hereinafter referred to as FeCo, FeNi, NiCo） coated cenospheres were prepared by heterogeneous precipitation under optimized conditions. Magnetic binary alloy coated cenosphere composites with core-shell structure were subsequently obtained by thermal reduction of the as-prepared precursors at 700℃ for 2 h under H2/N2 atmosphere. The results showed that the alloy coatings were uniform and the binary alloy coated cenosphere composites basically retained the spherical morphology, suggesting that the thickness of the alloy coating could be adjusted to fabricate core-shell composites with multilayer structures. The composites exhibited higher coercivity than the pure alloy powders, and could therefore be used for high-performance functional materials and devices.

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core-shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO3-2Ni（OH）2.2H2O- and Fe203.nH20-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core-shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600℃ for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders （lOg/L）, sulfate solution （0.2mol/L）, rate of adding reactants （3 mL/min） and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer （VSM）. The results show that the core-shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-Derformance functional materials and devices.