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Halide perovskites have gained significant attention in the field of photovoltaics and photocatalysis due to their exceptional optoelectronic properties. However, the exploration of other classes of 2D perovskite materials is limited. In this work, the photocatalytic performance of (HA)PbX4 2D crystals embedded with MoS2 in their bulk structure is investigated. The (HA)PbX4@MoS2 composites are directly synthesized in a (HA)PbX4 crystal solution. Notably, the (HA)PbI4@MoS2 composite exhibits a remarkable 2.94‐fold increase in H2 evolution activity. Furthermore, the composite demonstrated stability in a (HA)PbX4 (HA = histamine, X = I, Br, Cl)‐saturated aqueous HX solution. The photogenerated electrons in (HA)PbX4 are efficiently transferred to the MoS2 sites, facilitating the reduction of protons to H2. In this study, the potential of hybrid 2D perovskite–MoS2 composites is highlighted as promising visible‐light photocatalysts for aqueous solution applications. [ABSTRACT FROM AUTHOR]

The perovskite layer contains a large number of charged defects that seriously impair the efficiency and stability of perovskite solar cells (PSCs), thus it is essential to develop an effective passivation strategy to heal them. Based on theoretical calculations, it is found that enhancing the electrostatic potential of passivators can improve passivation effect and adsorption energy between charged defects and passivators. Herein, an electrostatic potential modulation (EPM) strategy is developed to design passivators for highly efficient and stable PSCs. With the EPM strategy, 1‐phenylethylbiguanide (PEBG) and 1‐phenylbiguanide (PBG) are designed. It is found that the charge distribution and electrostatic potential of phenyl‐ and phenylethyl‐ substituent on the biguanide are significantly enhanced. The N atom directly bonding to the phenyl group shows larger positive charge than that bonding to the phenylethyl group. The modulated electrostatic potential makes PBG bind stronger with the defects on perovskite surface. Based on the effective passivation of EPM, a champion efficiency of 24.67% is realized and the device retain 91.5% of its initial PCE after ≈1300 h. The promising EPM strategy, which provides a principle of passivator design and allows passivation to be controllable, may advance further optimization and application of perovskite solar cells toward commercialization. [ABSTRACT FROM AUTHOR]

Low‐dimensional perovskites (LDPs) have attracted significant attention due to their high stability, great chemical flexibility, and fertile "playground" for structural modulation, which are expected to herald the next‐generation multifunctional devices. While there is a high diversity of LDPs in the literature, the organic cations in most of the literature are still limited to amines. Here, the preparation of centimeter‐sized LDP single crystals with amidino‐based spacers is described, which enables systematic investigations on how halides initiate different structural stacking and on their physical properties. The 4‐amidinopyridine (4AP) cation in (4AP)PbX4 (X = Br, I) is vertically distributed between the inorganic layers to form a two‐dimensional perovskite. While the Cl‐based exhibits one‐dimensional perovskitoid packing. The change of halogens from Cl to Br and I leads to a lower hydrogen bonding, hardness and activation energy of the crystal. Finally, the potential of these crystals for X‐ray detectors is demonstrated. The (4AP)PbBr4 device achieves the highest sensitivity among three devices (373.1 µC Gyair−1 cm−2, 10 V), benefiting from the balanced charge transport and ionic migration. It is anticipated that this work will lead to further studies on the exploration and physics of novel LDP with properties suitable for radiation detection. [ABSTRACT FROM AUTHOR]

Even though the perovskite solar cell has been so popular for its skyrocketing power conversion efficiency, its further development is still roadblocked by its overall performance, in particular long-term stability, large-area fabrication and stable module efficiency. In essence, the soft component and ionic–electronic nature of metal halide perovskites usually chaperonage large number of anion vacancy defects that act as recombination centers to decrease both the photovoltaic efficiency and operational stability. Herein, we report a one-stone-for-two-birds strategy in which both anion-fixation and associated undercoordinated-Pb passivation are in situ achieved during crystallization by using a single amidino-based ligand, namely 3-amidinopyridine, for metal-halide perovskite to overcome above challenges. The resultant devices attain a power conversion efficiency as high as 25.3% (certified at 24.8%) with substantially improved stability. Moreover, the device without encapsulation retained 92% of its initial efficiency after 5000 h exposure in ambient and the device with encapsulation retained 95% of its initial efficiency after >500 h working at the maximum power point under continuous light irradiation in ambient. It is expected this one-stone-for-two-birds strategy will benefit large-area fabrication that desires for simplicity. Long-term stability and stable efficiency are essential for large-area fabrication of perovskite solar cells. Here, the authors achieve in situ anion-fixation and undercoordinated-Pb passivation using amidino-based ligand, realizing maximum power conversion efficiency of 25.3% with T95 over 500 h. [ABSTRACT FROM AUTHOR]

• Three 2D perovskites were used for photocatalytic hydrogen production. • (PEA) 2 PbI 4 has suitable bandgap and its hydrogen evolution rate is 1.4 mmol/h. • Hydrogen production was improved after MoS 2 doping, especially for (PEA) 2 PbI 4. Here, three kinds of two-dimensional (2D) perovskites, (3AP)PbI 4 , (4AP)PbI 4 and (PEA) 2 PbI 4 , were used for photocatalytic hydrogen production. (PEA) 2 PbI 4 produced the most hydrogen, as high as 1.41 mmol h−1 g−1. To further improve the photocatalytic effect, MoS 2 was used to combine the crystals. With the assistance of MoS 2 , the (PEA) 2 PbI 4 @MoS 2 compound produced more hydrogen than did the pure (PEA) 2 PbI 4 , with a production of 2.51 mmol h−1 g−1. The reason is that a high surface photovoltage was established between the surface of the 2D perovskite and MoS 2 , which promoted charge separation, resulting in high hydrogen production. [ABSTRACT FROM AUTHOR]

Crystal silicon solar cells being the most successful photovoltaic devices have prevailed in the energy market for decades. To further improve the device performance, photon management is necessary. Herein, a CsPbBr3–Cs4PbBr6 perovskite quantum dot@ZnO/ethylene vinyl acetate copolymer downshifting composite film is coated on the silicon solar cell. This downshifting composite film helps to convert high‐energy (UV‐blue) photons to relatively low‐energy photons with a wavelength at about 500 nm, which possess higher sensitivity in silicon solar cells. The effects of tetra‐n‐heptylammonium bromide and Zn(C2H5)2 on composition, optical and luminescence properties of perovskite quantum dots are thoroughly investigated, and a clean quantum dot solution with strong luminescent intensity can be obtained. The perovskite quantum dot@ZnO/ethylene vinyl acetate composite film absolutely improves the efficiency of silicon solar cells by 1.18%. The value is much higher than pure ethylene vinyl acetate (0.42%) and composite film without ZnO (0.57%). Moreover, ZnO inclusion can inhibit Cs and Pb leakage and maintain the device working stability, which is helpful for their commercial application in the future. This study further reveals that the enhancement lies in carrier relaxation energy loss reduction. Herein, a low‐cost downshifting composite film with excellent environmental stability for silicon solar cells applications is proposed. [ABSTRACT FROM AUTHOR]

It has been reported that an overlayer of lower dimensional perovskite can effectively improve the properties of 3D perovskite solar cells. Here, 4‐aminobutyric acid (C4I) and 6‐aminocaproic acid iodides (C6I) are introduced onto the surface of the perovskite layer, forming a low‐dimensional (LD) capping layer on the 3D perovskite films for high‐performance devices. It is found that C4I forms a 2D perovskite layer, while C6I forms a 1D perovskite layer on the 3D perovskite surface. By using the LD capping layers, the integrated perovskite films show passivated surface traps, reduced defect density, improved carrier lifetimes, and altered band alignment, leading to improved fill factor and open‐circuit voltage and, hence, significantly higher device efficiency. The devices with the C4I and C6I capping layers achieve solar cell efficiencies as high as 23.48% and 23.11%, respectively. In addition, bare devices with the C4I and C6I integration maintain 93.73% and 91.58%, respectively, of their initial efficiencies after exposure to the ambient atmosphere for 2000 h, demonstrating much better stability than the pristine 3D holding only 83.30% of its initial efficiency. It appears that this 2D capping is more suitable for enhancing 3D perovskite performance for general photoelectronic applications than the 1D capping. [ABSTRACT FROM AUTHOR]

Ion migration is a key root‐cause of photocurrent instability in perovskite X‐ray detectors. Although 2D perovskite single crystal (PSC) is a good candidate to suppress ion migration compared with its 3D counterpart, its intrinsic stability still needs to be improved. In this work, it is first envisioned to conquer the ion migration by enhanced chemical bonding; the proposal is further confirmed by density functional theory calculations, in which the bonds are made stronger by introducing a fluorine atom into the ortho position of phenethylamine (o‐F‐PEA) to shorten the distance between adjacent organic cations in the crystal lattice for enhanced electrostatic interactions between the F atom and the neighboring benzene ring. It is further demonstrated experimentally that the activation energy for ion migration (AEIM) of (o‐F‐PEA)2PbI4 PSC is increased compared with that of (PEA)2PbI4 PSC. The improved AEIM is also confirmed by enhanced thermal stability. Consequently, the dark current in the (o‐F‐PEA)2PbI4 2D PSC X‐ray detectors is reduced by two times compared with the (PEA)2PbI4 reference. Furthermore, the detector shows the sensitivity of 1724.5 μC Gyair−1 cm−2 at 1250 V mm−1, and much improved photocurrent stability. [ABSTRACT FROM AUTHOR]

In perovskite solar cells, not only defects on the top perovskite film surface seriously affect device performance, those buried in the bottom perovskite–electron‐transfer layer (ETL) interface damage carrier extraction, transport, and device efficiency as well. Herein, a novel double‐sided passivation strategy is designed using a single π‐conjugation‐induced 1‐pyrenesulfonic acid sodium salt (PyNa+). It is found that it effectively passivates top and bottom interface defects to render high device performance. The π‐conjugated pyrene‐containing sodium salt electronically contributes to the surface band edges and influences the carrier dynamics by passivating defects at both top hole‐transfer layer (HTL)–perovskite and bottom perovskite–ETL interfaces. The density functional theory (DFT) calculation confirms that the Pb cluster and I—Pb antisite defects can be effectively passivated by the O···Pb coordination and electrostatic interaction of PyNa+. The carrier lifetimes are prolonged, the interface defect density is effectively reduced as measured by space‐charge‐limited current (SCLC). Through the double layer passivation of PyNa+, the device delivers improved power conversion efficiencies of 21.22% relative to that of a reference perovskite, and enhanced stability with 85% of original efficiency after 1440 h in atmospheric environment. Double‐sided passivation provides a comprehensive strategy for high‐performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Defects in perovskite layers usually cause nonradiative recombination, impairing device performance and stability. Here, fluoroethylamine (FC2H4NH3, FEA) is integrated into the perovskite film to passivate defects. By engineering of different amounts of fluorine in the molecule, it is found that when 2‐fluoroethylamine (1FEA), in which one F bonds to the first carbon atom at the end of the molecule's structure, is used, the F atoms appear to be distributed throughout the bulk to the very surface. When 2,2‐difluoroethylamine (2FEA) and 2, 2, 2‐trifluoroethylamine (3FEA) are used, F is prone to distribution in the bulk of the perovskite film, while there appears to be no detectable F content on the surface. With the FEA passivation, the nonradiative recombination is suppressed, the carrier‐lifetime is improved to 840.01 ns, and the film‐air interface offers greater hydrophobicity, especially in the case of 1FEA, where because it is distributed throughout the film thickness, it passivates more defects and delivers the highest efficiency, as much as 23.40%. The device with 3FEA shows the best environmental stability; specifically, the bare cell without any encapsulation maintains 87% of its initial efficiency after exposure to the ambient environment for 1200 h. [ABSTRACT FROM AUTHOR]

• The compounds of (C 4 N 2 H 6)PbI 3 and (C 4 N 2 H 6)PbBr 3 are obtained. • Crystal structures and optical band gaps of the two compounds are researched. • The new compounds increased the solar cell efficiency. Here, the crystal synthesis, crystal structures, optical band gaps and application in devices of (C 4 N 2 H 6)PbI 3 and (C 4 N 2 H 6)PbBr 3 are researched and discussed. Novel hybrid 1D perovskite single crystals based on pyrazine were obtained by reacting the organic cation C 4 N 2 H 6 with lead iodide and bromide. The band gaps of (C 4 N 2 H 6)PbI 3 and (C 4 N 2 H 6)PbBr 3 compounds are 2.71 and 2.82 eV, respectively, which consistent with the structure distortion. The 1D crystals of (Py)PbI 3 and (Py)PbBr 3 assisted the device efficiency from 20.15% to 22.12 and 22.38%, respectively. [ABSTRACT FROM AUTHOR]

Over the 316 stainless steel mesh supported La0.95Mg0.05Ni0.8Co0.2O3perovskite structured catalyst, undiluted methane was cracked into hydrogen and highly graphitic carbon nano-onions (CNOs) and wheat stalk chains, the former was first produced in cheaper and simpler way and the later was first discovered. The Fe-Cr nano-alloy was responsible for the formation of the CNOs while the Ni or Ni-Fe nano-alloy was for the formation of carbon nano-wheat stalk chains. This process realized the ultimate ideal goal for the natural gas utilization: zero emission, clean hydrogen production, zero waste, and highly valuable carbon recycling. Moreover, the capacitances of the CNOs were evaluated by the cyclic voltammetry at different scan rates. The result indicated the capacitance of the CNOs was higher than that of Vulcan XC-72 carbon black, showing their promising applications in supercapacitors. [ABSTRACT FROM AUTHOR]