Glycine-Functionalized CsPbBr3 Nanocrystals for Efficient Visible-Light Photocatalysis of CO2 Reduction

Capping ligands are indispensable for the preparation of metal-halide-perovskite (MHP) nanocrystals (NCs) with good stability; however, the long alkyl-chain capping ligands in conventional MHP NCs will be unfavorable for CO₂ adsorption and hinder the efficient carrier separation on the surface of MHP NCs, leading to inferior catalytic activity in artificial photosynthesis. Herein, CsPbBr₃ nanocrystals with short-chain glycine as ligand are constructed through a facile ligand-exchange strategy. Owing to the reduced hindrance of glycine and the presence of the amine group in glycine, the photogenerated carrier separation and CO₂ uptake capacity are noticeably improved without compromising the stability of the MHP NCs. The CsPbBr₃ nanocrystals with glycine ligands exhibit a significantly increased yield of 27.7 μmol g⁻¹ h⁻¹ for photocatalytic CO₂-to-CO conversion without any organic sacrificial reagents, which is over five times higher than that of control CsPbBr₃ NCs with conventional long alkyl-chain capping ligands.     

Nanocrystal/Metal–Organic Framework Hybrids as Electrocatalytic Platforms for CO2 Conversion

The tunable chemistry linked to the organic/inorganic components in colloidal nanocrystals (NCs) and metal–organic frameworks (MOFs) offers a rich playground to advance the fundamental understanding of materials design for various applications. Herein, we combine these two classes of materials by synthesizing NC/MOF hybrids comprising Ag NCs that are in intimate contact with Al‐PMOF ([Al₂(OH)₂(TCPP)]) (tetrakis(4‐carboxyphenyl)porphyrin (TCPP)), to form Ag@Al‐PMOF. In our hybrids, the NCs are embedded in the MOF while still preserving electrical contact with a conductive substrate. This key feature allows the investigation of the Ag@Al‐PMOFs as electrocatalysts for the CO₂ reduction reaction (CO₂RR). We show that the pristine interface between the NCs and the MOFs accounts for electronic changes in the Ag, which suppress the hydrogen evolution reaction (HER) and promote the CO₂RR. We also demonstrate a minor contribution of mass‐transfer effects imposed by the porous MOF layer under the chosen testing conditions. Furthermore, we find an increased morphological stability of the Ag NCs when combined with the Al‐PMOF. The synthesis method is general and applicable to other metal NCs, thus revealing a new way to think about rationally tailored electrocatalytic materials to steer selectivity and improve stability.     

Stable and Low‐Cost Mesoscopic CH3NH3PbI2Br Perovskite Solar Cells by using a Thin Poly(3‐hexylthiophene) Layer as a Hole Transporter

Mesoscopic perovskite solar cells using stable CH₃NH₃PbI₂Br as a light absorber and low‐cost poly(3‐hexylthiophene) (P3HT) as hole‐transporting layer were fabricated, and a power conversion efficiency of 6.64 % was achieved. The partial substitution of iodine with bromine in the perovskite led to remarkably prolonged charge carrier lifetime. Meanwhile, the replacement of conventional thick spiro‐MeOTAD layer with a thin P3HT layer has significantly reduced the fabrication cost. The solar cells retained their photovoltaic performance well when they were exposed to air without any encapsulation, presenting a favorable stability. The combination of CH₃NH₃PbI₂Br and P3HT may render a practical and cost‐effective solid‐state photovoltaic system. The superior stability of CH₃NH₃PbI₂Br is also promising for other photoconversion applications.     

Correlation between Interfacial Structures and Device Performance: The Double-Edged Sword Effect of Lead Iodide in Perovskite Solar Cells

The interfacial electronic structure of perovskite layers and transport layers is critical for the performance and stability of perovskite solar cells (PSCs). The device performance of PSCs can generally be improved by adding a slight excess of lead iodide (PbI₂) to the precursor solution. However, its underlying working mechanism is controversial. Here, we performed a comprehensive study of the electronic structures at the interface between CH₃NH₃PbI₃ and C₆₀ with and without the modification of PbI₂ using in situ photoemission spectroscopy measurements. The correlation between the interfacial structures and the device performance was explored based on performance and stability tests. We found that there is an interfacial dipole reversal, and the downward band bending is larger at the CH₃NH₃PbI₃/C₆₀ interface with the modification of PbI₂ as compared to that without PbI₂. Therefore, PSCs with PbI₂ modification exhibit faster charge carrier transport and slower carrier recombination. Nevertheless, the modification of PbI₂ undermines the device stability due to aggravated iodide migration. Our findings provide a fundamental understanding of the CH₃NH₃PbI₃/C₆₀ interfacial structure from the perspective of the atomic layer and insight into the double-edged sword effect of PbI₂ as an additive.     

Synthesis,characterization, and KOH activation of nanoporous carbon for increasing CO2 adsorption capacity

Ordered nanoporous carbons (ONCs) were prepared using a soft-templating method. To improve the CO₂ adsorption efficiency, ONCs were chemically activated to obtain high specific surface area and micro-/mesopore volume with different KOH amounts (i.e., 0, 1, 2, 3, and 4) as an activating agent. The prepared nanoporous carbons (NCs) materials were analyzed by low-angle X-ray diffraction for confirmation of synthesized ONCs structures. The structural properties of the NCs materials were analyzed by high-angle X-ray diffraction. The textural properties of the NCs materials were examined using the N₂/77 K adsorption isotherms according to the Brunauer–Emmett–Teller equation. The CO₂ adsorption capacity was measured by CO₂ isothermal adsorption at 298 K/1 bar. From the results, the NCs activated with KOH showed that the increasing specific surface areas and total pore volumes resulted in the enhancement of CO₂ adsorption capacity.     

Syntheses of indolo[3,2,1-d,e]phenanthridines and isochromeno[3,4-a] carbazoles: palladium catalyzed intramolecular arylation via C-H functionalization

A new synthetic route has been developed for the preparation of indolo[3,2,1-d,e]phenanthridines and isochromeno[3,4-a]carbazoles via palladium catalyzed intramolecular biaryl coupling reactions. The coupling reactions proceeded smoothly and in high yields under ligand-free conditions with the catalytic system Pd(OAc)₂/Cs₂CO₃/TBAB. Under optimized reaction conditions no halogen-reduced products were observed.     

Electrochemical CO2 reduction catalyzed by atomically precise alkynyl-protected Au7Ag8, Ag9Cu6, and Au2Ag8Cu5 nanoclusters: probing the effect of multi-metal core on selectivity

Doping metal nanoclusters (NCs) with another metal usually leads to superior catalytic performance toward CO₂ reduction reaction (CO₂RR), yet elucidating the metal core effect is still challenging. Herein, we report the systematic study of atomically precise alkynyl-protected Au₇Ag₈, Ag₉Cu₆, and Au₂Ag₈Cu₅ NCs toward CO₂RR. Au₂Ag₈Cu₅ prepared by a site-specific metal exchange approach from Ag₉Cu₆ is the first case of trimetallic superatom with full-alkynyl protection. The three M₁₅ clusters exhibited drastically different CO₂RR performance. Specifically, Au₇Ag₈ demonstrated high selectivity for CO formation in a wide voltage range (98.1% faradaic efficiency, FE, at −0.49 V and 89.0% FE at −1.20 V vs. RHE), while formation of formate becomes significant for Ag₉Cu₆ and Au₂Ag₈Cu₅ at more negative potentials. DFT calculations demonstrated that the exposed, undercoordinated metal atoms are the active sites and the hydride transfer as well as HCOO* stabilization on the Cu–Ag site plays a critical role in the formate formation. Our work shows that, tuning the metal centers of the ultrasmall metal NCs via metal exchange is very useful to probe the structure–selectivity relationships for CO₂RR.

We report the first all-alkynyl-protected Au₂Ag₈Cu₅ cluster, which adopts a M@M₈@M₆ core configuration similar with Au₇Ag₈/Ag₉Cu₆ clusters. The three clusters exhibited strong metal core effect toward CO₂RR, which was understood by DFT calculations.     

Phasengleichgewichte im System Tll-Pbl2

Phase Equilibria in the TlI? PbI₂ System The TlI? TlPbI₃ section of the quasibinary system TlI? PbI₂ was reinvestigated by thermoanalytical and X-ray methods in order to clear up a number of inconsistent data concerning the intermediate ternary phases and their stability regions. Differences between the resulting phase diagram and prior information in the literature are discussed.     

The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

In this paper we report on the influence of light and oxygen on the stability of CH₃NH₃PbI₃ perovskite‐based photoactive layers. When exposed to both light and dry air the mp‐Al₂O₃/CH₃NH₃PbI₃ photoactive layers rapidly decompose yielding methylamine, PbI₂, and I₂ as products. We show that this degradation is initiated by the reaction of superoxide (O₂^?) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O₂^? species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O₂^? generation is significantly reduced when the mp‐Al₂O₃ film is replaced with an mp‐TiO₂ electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH₃NH₃PbI₃ to a species without acid protons could improve tolerance to oxygen and enhance stability.     

Ligand-free Ag(I)-catalyzed carboxylative coupling of terminal alkynes,chloride compounds,and CO2

Simple silver(I) slats were found to be highly efficient and selective catalyst for carboxylative coupling of aryl- or alkyl-substituted terminal alkynes, CO₂, and various allylic, propargylic or benzylic chlorides to exclusively yield functionalized 2-alkynoates. The activity is about 300 times that of the previously reported N-heterocyclic carbene copper(I) catalytic system. The ligand-free silver(I) catalytic system showed the wide generality of substrates involving both functionalized terminal alkynes and chloride compounds.     

Third- and second-order optical nonlinearity of Ge-Ga-S-PbI2 chalcohalide glasses

Two series of metal iodide doped chalcohalide glasses (100−2x)GeS₂·xGa₂S₃·xPbI₂ (0?x?20) and (100−x)(0.8GeS₂·0.2Ga₂S₃)·xPbI₂ (0?x?15) were prepared and characterized. The microstructure of these glasses has been studied by Raman scattering spectra. Utilizing femtosecond time-resolved optical Kerr effect (OKE) technique at the wavelength of 820 nm, a largest third-order nonlinearity χ⁽³⁾ of 2.07×10⁻¹³ esu was obtained for the 90GeS₂·5Ga₂S₃·5PbI₂ glass, and it decreases with the addition of PbI₂ in both two series. After thermally poled, second-harmonic generation (SHG) has been observed in these glasses according to Maker fringe method and a large second-order nonlinearity χ⁽²⁾ as well as 4 pm/V was obtained for the 70GeS₂·15Ga₂S₃·15PbI₂ glass. The variations of χ⁽²⁾ and χ⁽³⁾ on glass composition are ascribed to the evolution of micro-structural units in glass. These novel chalcohalide glasses would be expected to be the promising candidate materials for nonlinear optical devices.     

Nanocrystalline Calcium Carbonate Hydroxyapatites Containing Multiwall Carbon Nanotubes: Synthesis and Physicochemical Characterization

Nanocomposites (NCs) based on carbonated calcium hydroxyapatite (CHA) (bioapatite, an analogue of the inorganic component of mammalian bone tissue), carbonate apatite (Ca₁₀(PO₄)₆CO₃, CA), and multiwall carbon nanotubes (CNTs) are prepared in the system CaCl₂–(NH₄)₂HPO₄–NH₄HCO₃–NH₃–CNT–H₂O (25°C) by coprecipitation of calcium and phosphorus salts with CNTs from aqueous solutions. The physicochemical properties of nanocomposites are studied as dependent on their formation conditions and composition using the solubility (residual concentrations) method and pH measurements. The composition, crystal structure, morphology, spectroscopic and thermal characteristics of the synthesized CHA/CNT and CA/CNT NCs are determined using chemical analysis, X-ray powder diffraction, thermal analysis, and IR spectroscopy. Either CHA/CNT NCs of composition Ca₁₀(PO₄)₆(CO₃)_x(OH)_2–2х · yCNT · zH₂O, where х = 0.2; 0.5; 0.8; y = 1, 2, 3; z = 6.8–10.8, or (when х = 1) CA/CNT NCs of composition Ca₁₀(PO₄)₆CO₃ · yCNT · zH₂O, where y = 1–3; z = 6.9–10.8, are formed as the carbonate and CNT contents of the NC increase. Our results favor the understanding of the effect of carbonization and CNTs on the metabolic formation of native bone tissue apatite and can be used for the design of efficient ceramics for bone implants.     

Single-Layer 2D Ni−BDC MOF Obtained in Supercritical CO2-Assisted Aqueous Solution

The development of an efficient strategy for fabricating two-dimensional metal-organic framework (MOF) nanosheets with high yield and high stability is desirable. Herein, we demonstrate for the first time that large, single-layer 2D nickel-benzene dicarboxylate (Ni−BDC) MOF nanosheets can be fabricated with the assistance of supercritical (SC) CO₂ in a pure aqueous system. Detailed experimental evidence reveals that the SC CO₂ molecule can exchange with the lattice-coordinated H₂O molecules, side-on coordinate with the metal Ni¹ sites on the Ni−BDC surface, and finally break the interlayer hydrogen bond to exfoliate the bulk Ni−BDC into a 2D MOF. More importantly, a thin SC CO₂ layer building up at the water−Ni−BDC interfaces can transform the pristine hydrophilic interface into a super-hydrophobic one. This super-hydrophobic layer at the water-MOF interface can effectively prevent dissociation, thus promoting the stability of Ni−BDC in aqueous system.     

Pd/ligand-free synthesis of thienopyranones via Cu-catalyzed coupling-cyclization in PEG 400 under ultrasound

A greener and practical synthesis of 5-substituted thieno[2,3-c]pyran-7-ones has been achieved via Cu-catalyzed coupling-cyclization of 3-iodothiophene-2-carboxylic acid with terminal alkynes in the presence of K₂CO₃ in PEG 400 under ultrasound irradiation. A range of thienopyranone derivatives were synthesized by using this inexpensive and Pd- and ligand-free methodology.     

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH₃NH₃PbI₃ (MAPbI₃) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fe_x) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃@PCN‐221(Fe_x) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃@PCN‐221(Fe_0.2) exhibits a record‐high total yield of 1559 μmol g^?1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN‐221(Fe_0.2) in the absence of perovskite QDs.     

A thioacetamide additive-based hybrid (MA0.5FA0.5)PbI3 perovskite solar cells crossing 21 % efficiency with excellent long term stability

An additive in hybrid perovskite is playing a vital role in the increment of power conversion efficiency (PCE), stability, and reproducibility of perovskite solar cells (PVSCs). Although, single-phase α-FAPbI₃ perovskite has an ideal band gap but is continuously transforming to δ–FAPbI₃, which is non-photoactive. Here, we controlled the methylammonium (MA) and formamidinium (FA) ratio in the (MA_xFA_1-x)PbI₃ perovskite composition and tuned its morphology with the help of the thioacetamide (TAA) Lewis base additive. The optimum MA:FA ratio and fine-tuning of TAA additive result in a highly crystalline, large grain size and smooth surface of the (MA_0.5FA_0.5)PbI₃ perovskite film. These highly uniform thin films with 850 nm grain size offered a superior interaction between the perovskite material and the electron transport layer (ETL) and a longer lifetime yielding a high PCE. The (MA_0.5FA_0.5)PbI₃+1% TAA-based champion device exhibited the highest PCE of 21.29% for a small area (0.09 cm²) and 18.32% PCE for a large area (1 cm²). The TAA-assisted devices exhibited high stability with >85% retention over 500 h. These results suggest that the (MA_0.5FA_0.5)PbI₃ along with the 1% TAA additive is a promising absorber layer that can produce >21% PCE.     

A Modified Sequential Deposition Route for High-Performance Carbon-Based Perovskite Solar Cells under Atmosphere Condition

Carbon-based hole transport material (HTM)-free perovskite solar cells have exhibited a promising commercialization prospect, attributed to their outstanding stability and low manufacturing cost. However, the serious charge recombination at the interface of the carbon counter electrode and titanium dioxide (TiO₂) suppresses the improvement in the carbon-based perovskite solar cells’ performance. Here, we propose a modified sequential deposition process in air, which introduces a mixed solvent to improve the morphology of lead iodide (PbI₂) film. Combined with ethanol treatment, the preferred crystallization orientation of the PbI₂ film is generated. This new deposition strategy can prepare a thick and compact methylammonium lead halide (MAPbI₃) film under high-humidity conditions, which acts as a natural active layer that separates the carbon counter electrode and TiO₂. Meanwhile, the modified sequential deposition method provides a simple way to facilitate the conversion of the ultrathick PbI₂ capping layer to MAPbI₃, as the light absorption layer. By adjusting the thickness of the MAPbI₃ capping layer, we achieved a power conversation efficiency (PCE) of 12.5% for the carbon-based perovskite solar cells.     

Photoluminescence and Raman spectroscopy studies on polyaniline/PbI2 composite

Functionalization of PbI₂ with conjugated polymers (polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES)) is demonstrated by Raman and luminescence studies. PbI₂/PANI hybrid material was prepared by electrochemical polymerization of aniline onto the PbI₂ modified Pt electrode and mechanico-chemical reaction between the two constituents. PANI interacting with the PbI₂ gives rise to new Raman bands at 80, 144 and 170 cm⁻¹. First line reveals the formation of “stacking faults” that disrupt the I-Pb-I layers stacking along the c axis by the insertion of polymer molecules. The bands at 144 and 170 cm⁻¹ are attributed to the vibrational mode associated with Pb-NHR″₂ (R″=C₆H₄) bond. The functionalization of PbI₂ with PANI-EB brings forth the PANI-ES form. Depending on the semiconducting (PANI-EB) or conducting (PANI-ES) properties of the polymer in the PbI₂/PANI intercalated material, a partial or total collection of the charges generated under band to band irradiation is revealed by photoluminescence studies.     

First-Principles Study of Aziridinium Lead Iodide Perovskite for Photovoltaics

The long-term stability remains one of the main challenges for the commercialization of the rapidly developing hybrid organic-inorganic perovskite solar cells. Herein, we investigate the electronic and optical properties of the recently reported hybrid halide perovskite (CH₂)₂NH₂PbI₃ (AZPbI₃), which exhibits a much better stability than the popular halide perovskites CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃, by using density functional theory (DFT). We find that AZPbI₃ possesses a band gap of 1.31 eV, ideal for single-junction solar cells, and its optical absorption is comparable with those of the popular CH₃NH₃PbI₃ and HC(NH₂)₂PbI₃ materials in the whole visible-light region. In addition, the conductivity of AZPbI₃ can be tuned from efficient p-type to n-type, depending on the growth conditions. Besides, the charge-carrier mobilities and lifetimes are unlikely hampered by deep transition energy levels, which have higher formation energies in AZPbI₃ according to our calculations. Overall, we suggest that the perovskite AZPbI₃ is an excellent candidate as a stable high-performance photovoltaic absorber material.     

Optimizing the Atomic Layer Deposition of Alumina on Perovskite Nanocrystal Films by Using O2 As a Molecular Probe

Encapsulation methods have shown to be effective in imparting improved stability to metal-halide perovskite nanocrystals (NCs). Atomic layer deposition (ALD) of metal oxides is one of the promising approaches for such encapsulation, yet better control on the process parameters are required to achieve viable lifetimes for several optoelectronic and photocatalytic applications. Herein, we optimize the ALD process of amorphous aluminum oxide (AlO_x) as an encapsulating layer for CsPbBr₃ NC thin films by using oxygen (O₂) as a molecular diffusion probe to assess the uniformity of the deposited AlO_x layer. When O₂ reaches the NC surface, it extracts the photogenerated electrons, thus quenching the PL of the CsPbBr₃ NCs. As the quality of the ALD layer improves, less quenching is expected. We compare three different ALD deposition modes. We find that the low temperature/high temperature and the exposure modes improve the quality of the alumina as a gas barrier when compared with the low temperature mode. We attribute this result to a better diffusion of the ALD precursor throughout the NC film. We propose the low temperature/high temperature as the most suitable mode for future implementation of multilayered coatings.