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Terpyridine-substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl-crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn2+ ions allowed for layer-by-layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid-state dye-sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed. [ABSTRACT FROM AUTHOR]

Direct laser interference patterning (DLIP) is a versatile technique for surface patterning that enables formation of micro-nano sized periodic structures on top of the target material. In this study, DLIP in high pressure, supercritical and liquid CO2 by 4-beam DLIP was used to pattern titanium and zinc targets. Field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy was used to characterize the patterned surfaces. Field emission SEM analysis showed presence of ordered uniform donut ring pattern with hollow centers for both titanium and zinc with a period slightly under 3 µm while topographical images from atomic force microscopy revealed donut rings protruding outwards typically around 200 nm from target surface and consisted of a crevice at the center with a depth typically around 300 nm and 250 nm for titanium and zinc target, respectively. Based on X-ray photoelectron spectroscopic analysis, this is the first study to report formation of TiO2, TiC, ZnCO3, and zinc hydroxy carbonate on the pattern by DLIP in supercritical and liquid CO2 for titanium and zinc targets. Pressurized CO2 is demonstrated as a promising environment with mirror-based DLIP system for reactive patterning. Due to the superior transport properties and solvent power of supercritical CO2, the current study opens possibilities for reactive patterning in environments that may not have been previously possible. [ABSTRACT FROM AUTHOR]

Direct laser interference patterning (DLIP) is a versatile technique for surface patterning that enables formation of micro-nano sized periodic structures on top of the target material. In this study, DLIP in high pressure, supercritical and liquid CO2 by 4-beam DLIP was used to pattern titanium and zinc targets. Field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy was used to characterize the patterned surfaces. Field emission SEM analysis showed presence of ordered uniform donut ring pattern with hollow centers for both titanium and zinc with a period slightly under 3 µm while topographical images from atomic force microscopy revealed donut rings protruding outwards typically around 200 nm from target surface and consisted of a crevice at the center with a depth typically around 300 nm and 250 nm for titanium and zinc target, respectively. Based on X-ray photoelectron spectroscopic analysis, this is the first study to report formation of TiO2, TiC, ZnCO3, and zinc hydroxy carbonate on the pattern by DLIP in supercritical and liquid CO2 for titanium and zinc targets. Pressurized CO2 is demonstrated as a promising environment with mirror-based DLIP system for reactive patterning. Due to the superior transport properties and solvent power of supercritical CO2, the current study opens possibilities for reactive patterning in environments that may not have been previously possible. [ABSTRACT FROM AUTHOR]

[Display omitted] Atomic layer deposited (ALD) TiO 2 thin films have a wide range of applications in photonics which are, however, limited by the chemical instability of the amorphous as-deposited TiO 2. Post-deposition annealing is required for improving the performance by inducing phase transitions and oxide defects. ALD precursor traces remaining in the TiO 2 film affect the thermally-induced processes but the understanding of the effect of growth temperature on precursor traces in the film as well as on the thermally-induced processes is weak. In this study 30 nm ALD TiO 2 was grown on Si wafer from tetrakis(dimethylamido)titanium and water at 100–200 °C. TiO 2 was subsequently annealed in vacuum at 200–500 °C. Increasing the growth temperature decreased the amount of N bearing precursor traces and thus makes the TiO 2 more easily reducible. The reduction takes place simultaneously with the crystallization and formation of O 1 − defects. Vacuum annealing of TiO 2 with less than 0.3 at% of N results in nanocrystalline rutile whereas samples with more N containing traces crystallized as microcrystalline anatase. Nanocrystalline rutile TiO 2 was chemically stable and resistant to the dissolution at the grain boundaries under alkaline conditions making it a suitable material for protective photoelectrode coatings used in artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Lead-free layered double perovskite nanocrystals (NCs), i.e., Cs 4 M(II)M(III) 2 Cl 12 , have recently attracted increasing attention for potential optoelectronic applications due to their low toxicity, direct bandgap nature, and high structural stability. However, the low photoluminescence quantum yield (PLQY, <1%) or even no observed emissions at room temperature have severely blocked the further development of this type of lead-free halide perovskites. Herein, two new layered perovskites, Cs 4 CoIn 2 Cl 12 (CCoI) and Cs 4 ZnIn 2 Cl 12 (CZnI), are successfully synthesized at the nanoscale based on previously reported Cs 4 CuIn 2 Cl 12 (CCuI) NCs, by tuning the M(II) site with different transition metal ions for lattice tailoring. Benefiting from the formation of more self-trapped excitons (STEs) in the distorted lattices, CCoI and CZnI NCs exhibit significantly strengthened STE emissions toward white light compared to the case of almost non-emissive CCuI NCs, by achieving PLQYs of 4.3% and 11.4% respectively. The theoretical and experimental results hint that CCoI and CZnI NCs possess much lower lattice deformation energies than that of reference CCuI NCs, which are favorable for the recombination of as-formed STEs in a radiative way. This work proposes an effective strategy of lattice engineering to boost the photoluminescent properties of lead-free layered double perovskites for their future warm white light-emitting applications., (© 2024 The Authors. Small published by Wiley‐VCH GmbH.)

Cu 2 AgBiI 6 (CABI) is a promising perovskite-inspired absorber for solar cells due to its direct band gap and high absorption coefficient. However, the nonradiative recombination caused by the high extrinsic trap density limits the performance of CABI-based solar cells. In this work, we employ halide engineering by doping bromide anions (Br - ) in CABI thin films, in turn significantly improving the power conversion efficiency (PCE). By introducing Br - in the synthetic route of CABI thin films, we identify the optimum composition as CABI-10Br (with 10% Br at the halide site). The tailored composition appears to reduce the deep trap density as shown by time-resolved photoluminescence and transient absorption spectroscopy characterizations. This leads to a dramatic increase in the lifetime of charge carriers, which therefore improves both the external quantum efficiency and the integrated short-circuit current. The photovoltaic performance shows a significant boost since the PCE under standard 1 sun illumination increases from 1.32 to 1.69% (∼30% relative enhancement). Systematic theoretical and experimental characterizations were employed to investigate the effect of Br - incorporation on the optoelectronic properties of CABI. Our results highlight the importance of mitigating trap states in lead-free perovskite-inspired materials and that Br - incorporation at the halide site is an effective strategy for improving the device performance.

Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs 4 CuIn 2 Cl 12 layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs 4 CuIn 2 Cl 12 synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications.

Titanium dioxide (TiO 2 ) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO 2 coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO 2 /n + -Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H 2 O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO 2 coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO 2 coatings were amorphous and subject to photocorrosion. However, the TiO 2 coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO 2 into anatase TiO 2 . No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Cesium lead iodide (CsPbI 3 ) perovskite nanocrystals (NCs) suffer from a known transformation at room temperature from their red-emitting (black) to non-emitting (yellow) phase, induced by the tilting of PbI 6 octahedra. While the reported attempts to stabilize CsPbI 3 NCs mainly involve Pb 2+ -site doping as well as compositional and/or NC surface engineering, the black phase stability in relation only to the variation of the reaction temperature of CsPbI 3 NCs is surprisingly overlooked. We report a holistic study of the phase stability of CsPbI 3 NCs, encompassing dispersions, films, and even devices by tuning the hot-injection temperature between 120-170 °C. Our findings suggest that the transition from the black to the yellow phase occurs after over a month for NCs synthesized at 150 °C (150@NCs). Structural refinement studies attribute the enhanced stability of 150@NCs to their observed lowest octahedral distortion. The 150@NCs also lead to stable unencapsulated solar cells with unchanged performance upon 26 days of shelf storage in dry air. Our study underlines the importance of scrutinizing synthesis parameters for designing stable perovskite NCs towards long-lasting optoelectronic devices.

Titanium dioxide (TiO 2 ) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO 2 in devices incorporating organic or polymer components. In this study, we exploited low temperature (100-150 °C) atomic layer deposition (ALD) of 30 nm TiO 2 thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO 2 thin films grown at 150 °C and heat-treated at as low as 300 °C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300-500 °C. The average carrier lifetime for amorphous TiO 2 is few picoseconds but increases to >400 ps upon crystallization at 500 °C. The samples deposited at 100 °C were also crystallized as anatase but the carrier lifetime was <100 ps.

Visually black, electrically leaky, amorphous titania (am-TiO 2 ) thin films were grown by atomic layer deposition (ALD) for photocatalytic applications. Broad spectral absorbance in the visible range and exceptional conductivity are attributed to trapped Ti 3+ in the film. Oxidation of Ti 3+ upon heat treatment leads to a drop in conductivity, a color change from black to white, and crystallization of am-TiO 2 . ALD-grown black TiO 2 , without any heat treatment, is subject to dissolution in alkaline photoelectrochemical conditions. The best photocatalytic activity for solar water splitting is obtained for completely crystalline white TiO 2 .

Amorphous titanium dioxide (a-TiO 2 ) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO 2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO 2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO 2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO 2 . The surface analysis allows us to interpret the improved stability to the thermally induced formation of O - species within a-TiO 2 that are essentially electronic defects in the anionic framework., Competing Interests: The authors declare no competing financial interest.

Terpyridine-substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl-crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn(2+) ions allowed for layer-by-layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid-state dye-sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)