Solution-Processable Cu3BiS3 Thin Films: Growth Process Insights and Increased Charge Generation Properties by Interface Modification

Cu3BiS3 thin films are fabricated via spin coating of precursor solutions containing copper and bismuth xanthates onto planar glass substrates or mesoporous metal oxide scaffolds followed by annealing at 300 °C to convert the metal xanthates into copper bismuth sulfide. Detailed insights into the film formation are gained from time-resolved simultaneous small and wide angle X-ray scattering measurements. The Cu3BiS3 films show a high absorption coefficient and a band gap of 1.55 eV, which makes them attractive for application in photovoltaic devices. Transient absorption spectroscopic measurements reveal that charge generation yields in mesoporous TiO2/Cu3BiS3 heterojunctions can be significantly improved by the introduction of an In2S3 interlayer, and long-lived charge carriers (t50% of 10 μs) are found.

Molybdenum(III) Amidinate: Synthesis, Characterization, and Vapor Phase Growth of Mo-Based Materials

The synthesis, characterization, and thermogravimetric analysis of tris(N,N'-di-isopropylacetamidinate)molybdenum(III), Mo(iPr-AMD)₃, are reported. Mo(iPr-AMD)₃ is a rare example of a homoleptic mononuclear complex of molybdenum(III) and fills a longstanding gap in the literature of transition metal(III) trisamidinate complexes. Thermogravimetric analysis (TGA) reveals excellent volatilization at elevated temperatures, pointing to potential applications as a vapor phase precursor for higher temperature atomic layer deposition (ALD), or chemical vapor deposition (CVD) growth of Mo-based materials. The measured TGA temperature window was 200-314 °C for samples in the 3-20 mg range. To validate the utility of Mo(iPr-AMD)₃, we demonstrate aerosol-assisted CVD growth of MoO₃ from benzonitrile solutions of Mo(iPr-AMD)₃ at 500 °C using compressed air as the carrier gas. The resulting films are characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. We further demonstrate the potential for ALD growth at 200 °C with a Mo(iPr-AMD)₃/Ar purge/300 W O₂ plasma/Ar purge sequence, yielding ultrathin films which retain a nitride/oxynitride component. Our results highlight the broad scope utility and potential of Mo(iPr-AMD)₃ as a stable, high-temperature precursor for both CVD and ALD processes.

Charged Particle-Induced Surface Reactions of Organometallic Complexes as a Guide to Precursor Design for Electron- and Ion-Induced Deposition of Nanostructures

Focused electron beam-induced deposition (FEBID) and focused ion beam-induced deposition (FIBID) are direct-write fabrication techniques that use focused beams of charged particles (electrons or ions) to create 3D metal-containing nanostructures by decomposing organometallic precursors onto substrates in a low-pressure environment. For many applications, it is important to minimize contamination of these nanostructures by impurities from incomplete ligand dissociation and desorption. This spotlight on applications describes the use of ultra high vacuum surface science studies to obtain mechanistic information on electron- and ion-induced processes in organometallic precursor candidates. The results are used for the mechanism-based design of custom precursors for FEBID and FIBID.

Nanocrystal Precursor Incorporating Separated Reaction Mechanisms for Nucleation and Growth to Unleash the Potential of Heat-up Synthesis

A heat-up method for quantum dots (QDs) synthesis holds distinctive benefits for large-scale production with its simplicity, scalability, and high reproducibility. Its applications, however, have been limited because it inevitably yields a strong overlap between the nucleation and the growth stages. We addressed this long-standing problem by introducing a precursor having separated reaction paths for nucleation and growth. Unlike existing precursors, which employ a shared intermediate for both reactions, 9-mercapto-9-borabicyclo[3.3.1]nonane (BBN-SH) induces growth via surface-assisted conversion and drives nucleation via cluster formation in solution. Furthermore, this precursor chemistry embeds an efficient mechanism to suppress nucleation during growth. As such, BBN-SH allows heat-up-based growth of high-quality shells that are comparable to those created by the injection method. It is also notable that BBN-SH-based heat-up synthesis shows mitigated sensitivity to temperature fluctuation; therefore, it is highly suitable for industrial-scale reactions. We established a simple, scalable, and economic scheme for core/shell QDs by streamlining quantitative core synthesis and heat-up-based shell growth and showed that the scheme produces QDs of comparable quality to those produced by the traditional method. Here, we introduce a precursor that drives a distinctive mode of nanoparticle growth. We anticipate our study to inspire the design of other precursors and unleash the full potential of heat-up synthesis.

Engineering Halide Perovskite Crystals through Precursor Chemistry

The composition, crystallinity, morphology, and trap-state density of halide perovskite thin films critically depend on the nature of the precursor solution. A fundamental understanding of the liquid-to-solid transformation mechanism is thus essential to the fabrication of high-quality thin films of halide perovskite crystals for applications such as high-performance photovoltaics and is the topic of this Review. The roles of additives on the evolution of coordination complex species in the precursor solutions and the resulting effect on perovskite crystallization are presented. The influence of colloid characteristics, DMF/DMSO-free solutions and the degradation of precursor solutions on the formation of perovskite crystals are also discussed. Finally, the general formation mechanism of perovskite thin films from precursor solutions is summarized and some questions for further research are provided.

Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite: Compatibility and Performance

The compatibility of atomic layer deposition directly onto the mixed halide perovskite formamidinium lead iodide:methylammonium lead bromide (CH(NH₂)₂, CH₃NH₃)Pb(I,Br)₃ (FAPbI₃:MAPbBr₃) perovskite films is investigated by exposing the perovskite films to the full or partial atomic layer deposition processes for the electron selective layer candidates ZnO and SnO_x. Exposing the samples to the heat, the vacuum, and even the counter reactant of H₂O of the atomic layer deposition processes does not appear to alter the perovskite films in terms of crystallinity, but the choice of metal precursor is found to be critical. The Zn precursor Zn(C₂H₅)₂ either by itself or in combination with H₂O during the ZnO atomic layer deposition (ALD) process is found to enhance the decomposition of the bulk of the perovskite film into PbI₂ without even forming ZnO. In contrast, the Sn precursor Sn(N(CH₃)₂)₄ does not seem to degrade the bulk of the perovskite film, and conformal SnO_x films can successfully be grown on top of it using atomic layer deposition. Using this SnO_x film as the electron selective layer in inverted perovskite solar cells results in a lower power conversion efficiency of 3.4% than the 8.4% for the reference devices using phenyl-C₇₀-butyric acid methyl ester. However, the devices with SnO_x show strong hysteresis and can be pushed to an efficiency of 7.8% after biasing treatments. Still, these cells lacks both open circuit voltage and fill factor compared to the references, especially when thicker SnO_x films are used. Upon further investigation, a possible cause of these losses could be that the perovskite/SnO_x interface is not ideal and more specifically found to be rich in Sn, O, and halides, which is probably a result of the nucleation during the SnO_x growth and which might introduce barriers or alter the band alignment for the transport of charge carriers.

Unearthing [3-(Dimethylamino)propyl]aluminium(III) Complexes as Novel Atomic Layer Deposition (ALD) Precursors for Al2 O3 : Synthesis, Characterization and ALD Process Development

Identification and synthesis of intramolecularly donor-stabilized aluminium(III) complexes, which contain a 3-(dimethylamino)propyl (DMP) ligand, as novel atomic layer deposition (ALD) precursors has enabled the development of new and promising ALD processes for Al₂ O₃ thin films at low temperatures. Key for this promising outcome is the nature of the ligand combination that leads to heteroleptic Al complexes encompassing optimal volatility, thermal stability and reactivity. The first ever example of the application of this family of Al precursors for ALD is reported here. The process shows typical ALD like growth characteristics yielding homogeneous, smooth and high purity Al₂ O₃ thin films that are comparable to Al₂ O₃ layers grown by well-established, but highly pyrophoric, trimethylaluminium (TMA)-based ALD processes. This is a significant development based on the fact that these compounds are non-pyrophoric in nature and therefore should be considered as an alternative to the industrial TMA-based Al₂ O₃ ALD process used in many technological fields of application.

CsI Pre-Intercalation in the Inorganic Framework for Efficient and Stable FA1-x Csx PbI3 (Cl) Perovskite Solar Cells

Engineering the chemical composition of organic and inorganic hybrid perovskite materials is one of the most feasible methods to boost the efficiency of perovskite solar cells with improved device stability. Among the diverse hybrid perovskite family of ABX₃ , formamidinium (FA)-based mixed perovskite (e.g., FA_1-x Cs_x PbI₃ ) possesses optimum bandgaps, superior optoelectronic property, as well as thermal- and photostability, which is proven to be the most promising candidate for advanced solar cell. Here, FA_0.9 Cs_0.1 PbI₃ (Cl) is implemented as the light-harvesting layer in planar devices, whereas a low temperature, two-step solution deposition method is employed for the first time in this materials system. This paper comprehensively exploits the role of Cs⁺ in the FA_0.9 Cs_0.1 PbI₃ (Cl) perovskite that affects the precursor chemistry, film nucleation and grain growth, and defect property via pre-intercalation of CsI in the inorganic framework. In addition, the resultant FA_0.9 Cs_0.1 PbI₃ (Cl) films are demonstrated to exhibit an improved optoelectronic property with an elevated device power conversion efficiency (PCE) of 18.6%, as well as a stable phase with substantial enhancement in humidity and thermal stability, as compared to that of FAPbI₃ (Cl). The present method is able to be further extended to a more complicated (FA,MA,Cs)PbX₃ material system by delivering a PCE of 19.8%.

Polymer-Derived Silicoboron Carbonitride Foams for CO2 Capture: From Design to Application as Scaffolds for the in Situ Growth of Metal-Organic Frameworks

A template-assisted polymer-derived ceramic route is investigated for preparing a series of silicoboron carbonitride (Si/B/C/N) foams with a hierarchical pore size distribution and tailorable interconnected porosity. A boron-modified polycarbosilazane was selected to impregnate monolithic silica and carbonaceous templates and form after pyrolysis and template removal Si/B/C/N foams. By changing the hard template nature and controlling the quantity of polymer to be impregnated, controlled micropore/macropore distributions with mesoscopic cell windows are generated. Specific surface areas from 29 to 239 m(2)  g(-1) and porosities from 51 to 77 % are achieved. These foams combine a low density with a thermal insulation and a relatively good thermostructural stability. Their particular structure allowed the in situ growth of metal-organic frameworks (MOFs) directly within the open-cell structure. MOFs offered a microporosity feature to the resulting Si/B/C/N@MOF composite foams that allowed increasing the specific surface area to provide CO2 uptake of 2.2 %.

Modification of different zirconium propoxide precursors by diethanolamine. Is there a shelf stability issue for sol-gel applications?

Modification of different zirconium propoxide precursors with H₂dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(OⁿPr)(OⁱPr)₃(ⁱPrOH)]₂ with ½ a mol equivalent of H₂dea the complexes [Zr₂(OⁿPr)₆(OCH₂CH₂)₂NH]₂ (1) and [Zr₂(OⁿPr)₂(OⁱPr)₄(OCH₂CH₂)₂NH]₂ (2) were obtained. However, ¹H-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either ½ or 1 equivalent mol of H₂dea results in formation of the trinuclear complex, Zr{η³μ₂-NH(C₂H₄O)₂}₃[Zr(OⁱPr)₃]₂(iPrOH)₂ (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors.