Film Deposition Research Articles

Strategies for alkali-free synthesis, surface modification, and electrophoretic deposition of composite films for biomedical applications

This investigation addresses increasing interest in composites for biomedical applications and advanced methods for their synthesis and electrophoretic deposition (EPD). The feasibility of preparation of hydroxyapatite (HA), titania and zirconia particles using branched polyethylenimine polymer (BPEI) or L-arginine amino acid as organic alkalizers is demonstrated. In this new approach, BPEI and L-arginine are used as alkalizers-capping agents instead of inorganic alkalis. The use of BPEI facilitates synthesis of HA nanorods with reduced size. This approach opens an avenue for the fabrication of nanoparticles of other functional inorganic materials using alkalizers-capping agents. It offers advantages of simple procedure, environmental benefits and improved control of particle size. Composite films are obtained by cathodic EPD using linear polyethylenimine (LPEI) as a charging and film-forming agent. A conceptually new approach is developed for anodic EPD of alginic acid polymer (AlgH) and composite films containing drug molecules in AlgH matrix. This strategy involves the use of L-arginine as an alkalizer for solubilization of drugs, which exhibit poor solubility in water. AlgH and drug molecules are solubilized in water and deposited by anodic EPD. Testing results confirm the fabrication of composite films, containing drug molecules. This method allows reduced gas evolution at the electrode, elimination of film porosity, improved stabilization of bioceramic particles in polymer solutions and facilitates composite film formation from stable suspensions. The deposition methods developed in this investigation can be used for deposition of other cationic and anionic polymers and their co-EPD with bioceramics, drugs and other functional materials.

Sputter deposited silver niobate thin films: Pathway towards phase purity

The quest for environmentally sustainable alternatives to lead-based dielectric materials in dielectric capacitors has led research to the exploration of options such as silver niobate (AgNbO3), which has been found to display excellent energy storage properties. Homogeneity and phase-purity of the used thin films are vital for optimal performance of these devices. In this study, a systematic variation of oxygen partial pressure and bias voltage during reactive d.c. magnetron co-sputtering from metallic targets is employed to synthesise AgNbO3 thin films. Structural and chemical composition of the films are investigated using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, elastic recoil detection analysis, and Rutherford backscattering spectrometry. The findings emphasise the necessity of precise parameter control during deposition to avoid the presence of undesirable secondary phases like Ag and Ag2Nb4O11 and to ensure the formation of homogeneous and phase-pure AgNbO3 thin films. The gained insights demonstrate the potential of reactive d.c. magnetron sputtering for the deposition of lead-free AgNbO3 thin films, offering pathways for enhanced environmental compatibility of future dielectric capacitors.

Understanding vapor phase growth of hexagonal boron nitride.

Hexagonal boron nitride (hBN), with its atomically flat structure, excellent chemical stability, and large band gap energy (∼6 eV), serves as an exemplary 2D insulator in electronics. Additionally, it offers exceptional attributes for the growth and encapsulation of semiconductor transition metal dichalcogenides (TMDCs). Current methodologies for producing hBN thin films primarily involve exfoliating multi-layer or bulk crystals and thin film growth via chemical vapor deposition (CVD), which entails the thermal decomposition and surface reaction of molecular precursors like ammonia boranes (NH3BH3) and borazine (B3N3H6). These molecular precursors contain pre-existing B-N bonds, thus promoting the nucleation of BN. However, the quality and phase purity of resulting BN films are greatly influenced by the film preparation and deposition process conditions that remain a substantial concern. This study aims to comprehensively investigate the impact of varied CVD systems, parameters, and precursor chemistry on the synthesis of high-quality, large scale hBN on both catalytic and non-catalytic substrates. The comparative analysis provided new insights into most effective approaches concerning both quality and scalability of vapor phase grown hBN films.

Preparation of ultrathin sputtered gold films on palladium as efficient oxygen reduction electro-catalysts

Herein, we present the preparation of ultrathin gold (Au) films on different M (M = Pd, Pt, Rh, Ir, and Ru) electrodes (Au/M) using magnetron sputtering deposition for oxygen reduction reaction (ORR). The ORR electro-catalytic activities of prepared Au/M catalysts increase as follows: Au/Ru < Au/Ir < Au/Rh < Au/Pt < Au/Pd. Accordingly, the oxygen reduction catalytic behaviors of the Au-modified palladium (Au/Pd) thin films with various Au thicknesses (0.16, 0.24, 0.5, and 1 nm) are investigated in acidic environments. It is found that Au modifications can promote oxygen reduction performances due to the development of more catalytic active sites on the Pd catalyst through the existence of Au atoms. Noticeably, Au/Pd samples exhibit a connection in oxygen reduction ability as a function of Au thickness, with the ultrathin 0.16 nm Au/Pd being the most active ORR catalyst. Significantly, the 0.16 nm Au/Pd material demonstrates superior stability after 1000 potential cycles compared with the 0.16 nm Pt/Pd owing to the influence of Au coating and structurally stable surfaces. Therefore, surface modification with the deposition of Au films on Pd represents a favorable technique to boost both the ORR capability and stability of the electro-catalysts.

Comparative study of the sensitivity of H2S and NO2 in CuInSe2 gas sensors that are fabricated using screen printing and MEMS Integration

This study compares the gas response efficiency of a gas sensor substrate that is produced using screen-printing (SP) and micro-electro-mechanical systems (MEMS) technology, followed by deposition of CuInSe2 (CIS) film layers by radio-frequency (RF) sputtering and hyperthermal annealing for gas sensing applications. The SP substrates are used for CIS film deposition for RF sputtering, followed by various hyperthermal annealing treatments. SEM observations of the CIS film surfaces after annealing show surface particles with a size distribution of 155 to 30 nm, which demonstrate a phenomenon that is similar to Ostwald ripening and which creates structural variation and unevenness after annealing. The CIS film/MEMS substrates (MEMSs) gas sensor substrates are evaluated using a NIR thermal camera to determine the optimal operating temperature for direct annealing, which is 203.2 °C. Gas sensing response tests show that only H2S or NO2 gas rapidly and significantly elicit a response but a CIS film/SPs gas sensor exhibits significant resistance signal noise. The CIS film/MEMSs gas sensor is more stable than CIS film/SPs (after annealing) so it is more suitable for gas sensing. SEM images confirm that the film remains intact, so it is suitable for gas sensing applications.

SILAR deposition and characterization of ZnO films for numerical investigation as electron transport layer in solar cells

The SILAR method of thin film deposition has attracted the scientific community over the years due to its easiness, low cost, availability of room temperature deposition, and more over due to the variation in properties of thin films available by varying deposition parameters.This work is carried out in a way to comprehensively compare two ZnO thin film samples prepared from precursor media with Zinc Acetate (S1) and Zinc Chloride(S2) salts deposited by SILAR method in Perovskite Solar cell applications. The XRD, FTIR, Raman, FESEM, and UV-Visible analysis were carried out for identifying the structural, morphological, and optical quality of these samples. The role of these samples as Electron Transport Layer (ETL) in Perovskite Solar cell were identified using General purpose PhotoVoltaic Device model (GPVDM) simulation software which is well adapted for studying Solar cell architecture. It provided the output Solar cell parameters like Jsc, Voc, FF, PCE, etc and by varying the active layer and Hole Transport Layer (HTL) thicknesses, the optimized efficiency of devices with samples S1 and S2 were obtained as 21.88% and 21.96%.The results showed that SILAR-synthesized ZnO thin films could be potential candidates for ETL applications in Perovskite Solar cells.

SRIM simulation of hydrogen ions interaction with bismuth oxide nanoparticles doped with rare earth elements

Simulation methods have received much attention across various fields in recent years. The rare-earth lutetium tantalate (LuTaO4) doped “Bismuth Oxide (Bi2O3) thin films were deposited onto polymer substrates using a SRIM program.” The SRIM program was used to calculate some physical characteristics of Bi2O3 films at energies between 1.0 MeV and 20 MeV. The “electronic and nuclear stopping powers” of LuTaO4, Bi2O3, C10H8O4, and LuTaO4/ Bi2O3/C10H8O4 samples were investigated. These findings show that rare earth doping may improve the performance of composite materials. The interaction of ion beams with matter can result in a wide variety of phenomena. The deposition of Bi2O3 films doped with LuTaO4 on C10H8O4 led to changes in the “electronic and nuclear stopping powers” and range in the materials. Published data were compared with the results obtained and the calculations parameters were provided.

A novel coaxial air-R134a spray cooling for heat transfer enhancement of laser dermatology

Efficient cooling is essential in laser dermatology to prevent thermal damage, but current methods are often hindered by thermal barrier film deposition. This study presents coaxial air-R134a spray cooling for heat transfer enhancement and deposited-film mitigation. Surface temperature was measured using a TFTC thermocouple, while heat flux was estimated through the improved Duhamel theorem. High-speed camera visualization with the Mie-scattering technique captured the spray and film behavior. The results showed uniform and effective cooling via transient surface heat transfer and film behaviors. The boiling curve identified three distinct cooling phases: transition boiling, nucleate boiling, and single-phase film deposition. Airflow adjustments not only enhance the heat transfer coefficient but also control spray dynamics, droplet rebounding, and film spreading. Self-organizing maps revealed that medium-to-high nozzle spacing (y/D) reduces surface temperature and increases the heat transfer coefficient. Film resistance time is minimized by either high airflow and low y/D or low airflow and high y/D. For critical heat flux, low y/D and airflow are optimal. A y/D = 32 and 60 L/min airflow provided appropriate operating conditions. However, airflow increased frost deposition during off-duty, suggesting moisture-free air in the future.

Enhanced etching of GaN with N2 gas addition during CVD diamond growth

Diamond on GaN materials processing is not straight-forward, as GaN is susceptible to a quasi-pure hydrogen CVD plasma etching. 1%, 3% and 5% N2 gas was gradually added to the H2 gas with fixed 6% CH4 in the recipe to promote the growth of diamond nanocrystals. Different types of microstructures were produced, with addition of nitrogen to the precursor gas recipe. Nitrogen gas changes the diamond film microstructure from faceted to spherical grains, with signs of GaN etching. The FWHM of the sp3 carbon Raman peak was calculated to be 6.5 cm−1, when there was no nitrogen gas in the precursor recipe, which deteriorates to a large extent after successive addition of N2. Fourier transform infrared spectroscopy (FTIR) showed a strong presence of the nitrogen related defects (peak positions at 1190 and 1299 cm−1) inside the nanocrystalline diamond (NCD) films grown with N2 addition. GaN layer etching from the base substrate by the CVD plasma was clearly evidenced by energy dispersive X-ray spectra (EDS) of the deposited films. Al elemental EDS peaks from the base sapphire substrate were observed for the films grown with nitrogen addition, but no Ga EDS peaks were detected. X-ray diffraction (XRD) micrographs further supported the enhanced GaN etching phenomenon. The electrical resistivity of the uncoated GaN was initially measured to be 22.2 Ω-cm. However, the resistivity rose to 1.59 × 106 Ω-cm after the nitrogen assisted film deposition; due to the GaN etching - thereby exposing the underlying insulating sapphire substrate.

Graphene-assisted remote epitaxy wrinkle-free GaN films on flexible mica

When GaN films were directly deposited onto fluorophlogopite mica substrates, spontaneous wrinkling was frequently observed in GaN films. Because of the non-uniform interface adhesion between GaN and mica, two types of delamination phenomena have been observed by scanning electron microscopy. The maximum thickness of wrinkle-free GaN films on mica substrates was ∼200 nm. Interface pinning effect occurred due to the dangling bonds caused by the damage to mica during the deposition of GaN films. To avoid the formation of dangling bonds, the surface of mica was shielded by a graphene interlayer which was transferred via a wet method. Wrinkles were eradicated after the formation of sliding contact between GaN films and fully graphene-covered mica substrates. Despite the presence of the graphene lattice, the growth of GaN epilayer remained governed by the potential field of mica, indicating that remote epitaxy occurred on a 2D mica support substrate.

Small-Molecule:Polymer Composites for Transparent Films with Visible Emission.

The analysis of the shift in photoluminescence emission for a blend of polyvinylcarbazole and acrylonitrile derivative compounds is reported. The small-molecule compounds have different functional groups, phenyl, pyridine, or methyl phenyl, attached to an acrylonitrile group. According to the functional group, the blue emission for pure dye shifts to green or yellowish in the blend film. Several PVK:dye ratios from 0:100 to 20:80 were used for film deposition. The film morphology was analyzed by atomic force microscopy; for low dye content, homogeneous films were achieved. However, aggregates of several micrometers are formed on the surface of films with higher dye concentrations. The shift in emission occurs only with PVK, and for a non-conjugated matrix such as polystyrene, the emission remains unchanged. The interaction of dyes with PVK leading to change in emission was also achieved by grinding dye and polymer. Results showed that shifts in emission could come from exciplex formation along with changes in dye intermolecular interactions. The blend films were highly transparent in the visible spectra due to the absorption in the UV region for dye and matrix. The films with ratio PVK: dye ratio 80:20 was used as active layer in OLEDs.

Facile preparation and study of supramolecular architecture of an efficient nanocomposite LB film AHSM/SA based on azo-functionalized hockey stick-shaped mesogen at air-water and air-solid interface

Hockey stick-shaped mesogens are fascinating thermotropic liquid crystal systems owing to their exceptional supramolecular assembly properties and shape anisotropy compared to conventional rod-and bent-shaped mesogens. In this article, we present an investigation of the supramolecular organization of a new azo-functionalized hockey stick-shaped mesogen with stearic acid at the air-water interface and air-solid interfaces by applying the Langmuir-Blodgett film deposition method. The incorporation of stearic acid can change the molecular organization of azo-functionalized hockey stick-shaped mesogen at an aqueous interface through hydrophobic-hydrophobic interactions and form a supramolecular nanostructure at the solid interface. The interfacial nature of the Langmuir monolayer was studied by recording the isotherm (surface pressure area, π–A), which was further analyzed by using Brewster angle microscopy. The significant reduction in molecular area, increased surface pressure, and lower isotherm slope of the AHSM/SA composite mixture indicate the hybrid AHSM/SA monolayer's greater stability compared to pure AHSM. BAM images of the AHSM/SA composite signify nanostructure aggregates formed by the interaction of AHSM and SA molecules at the air-water interface. Field emission scanning electron microscopic analysis of composite films revealed the formation of supramolecular domains. The impact of changing the surface pressure and the number of depositions on the morphology of the composite film surface was monitored using field emission scanning electron microscopy. The supramolecular H-type aggregation of azo-functionalized hockey stick-shaped mesogen and stearic acid molecules in the composite LB film was characterized using UV–visible absorption and steady-state fluorescence spectroscopy. The adsorption of stearic acid onto azo-functionalized hockey stick-shaped mesogen via hydrophobic interactions was confirmed by Fourier transform infrared spectroscopy of the composite Langmuir Blodgett film. Further, Raman spectroscopy of the LB films of the AHSM/SA composites is distinct from the pristine film components due to the merging of signals at similar wave numbers for both SA and AHSM with a lack of typical packing pattern further supported by PXRD studies of the films.

Electrodeposition Processes for Controlling Surface Morphology of Thick Cu2Se Films As Thermoelectric Conversion Materials

Copper selenides (Cu2Se) are a class of chalcogenides found in various applications owing to their semiconductor material properties. Cu2Se has shown great potential for thermoelectric (TE) device applications, and it has also demonstrated significant room for improvement at high temperatures owing to its phonon glass electron crystal (PGEC), an intrinsic property in potential thermoelectric materials1. Compact morphology and smooth surface are essential parameters in reducing the contact resistance between a thermoleg and the metal electrode2,3. Other studies have focused on further lowering thermal conductivity by increasing phonon drag through nano-structuring and introducing nano-inclusion4,5,6.Among synthesis approaches, the electrodeposition of TE materials appears promising. Morphology control in electrochemical deposition has been demonstrated and has shown outstanding results7. In a Bi2Se3 growth study, the films showed a simultaneous change in morphology, smooth to rough films, and phase, rhombohedral to orthorhombic, with film thickness. These phases exhibit different crystallite sizes and Seebeck coefficients8. It has been demonstrated that film growth and thickness by electrodeposition mainly depend on electrolyte composition and the applied potential to control morphology and stoichiometry. Most studies have focused on tuning these parameters,resulting in films with well-defined stoichiometry but with porous, mossy, or low compactness 9,10,11. There is, therefore, room for improvement, and a better understanding of the deposition processes is key to controlling the growth modes, morphology, and composition.In this work, we study the early stages of Cu2Se electrodeposition for TE application. Our goal is to optimize the electrodeposition conditions to obtain compact, well-crystallized films with Cu2Se stoichiometry. The films were obtained by potentiostatic deposition on a gold electrode from an acidic electrolyte, H2SO4 (pH 0.9 to 1.9), containing 10 mM CuSO4, (1 to 10 mM) H2SeO3, and the bath temperature varied from 25oC to 55oC. All potentials were measured and referred to Ag/Agl/sat, with a platinum mesh serving as the counter electrode. Results showed that at elevated temperature (55oC), pH 1.5, and a precursor concentration ratio [Cu(II) 10mM]/[Se(IV) 5mM] are suitable for Cu2Se film deposition. For films deposited in the potential range -500 mV ≤ V ≤ -50 mV, EDS analysis indicated that atomic composition is relatively constant and close to the desired Cu2Se stoichiometry (66.7 % Cu, 33.3 % Se). XRD spectra present sharp peaks corresponding to Cu2Se, indicating films are well crystallized, with an average crystallite size of 18 nm. SEM showed relatively smooth and compact films with, however, a high density of bulges. For films obtained at potentials more positive than -50 mV and more negative than -500 mV, notable changes in composition to Cu 60.8%, morphology, and the appearance of Cu3Se2 XRD peaks were observed, denoting the existence of mixed phases of Cu3Se2 and Cu2Se. Progress in the investigation of the growth mechanism/processes of Cu2Se films at the early deposition stages will also be presented.References T. Wei, Y.Qin, T. Deng, Q. Song, B. Jiang, R. Liu, P.Qiu, X. Shi, L. Chen,Sci. Chi. Mat. 62, 1, 8–24 (2019) P. Nieroda, A. Kusior, J. Leszczynski, P. Rutkowski, A. Kolezynski, Materials, 14, 3650 (2021)N. Su, S. Guo, F. Li, B. Li. Nanomaterials, 10, 431 (2020)S. Li, X. Lou, X. Li, J. Zhang, D. Li, H. Deng, J. Liu, G. Tang. Chemistry of Materials, 32 (22), 9761-9770, (2020)H. Zhang, D V. Talapin. Angew. Chem Int, 53, 9126-9127 (2014) N. K. Singh, S. Bathula, B. Gahtori, K Tyagi., D. Haranath, A. Dhar. Journal of Alloys and Compounds, 668, 152-158 (2016) K. Cicvaric, L. Meng, D. W. Newbrook, R. Huang, S. Ye, W. Zhang, A. L. Hector, G. Reid, P. N. Bartlett, C. H. K. Groot. ACS Omega , 5, 24, 14679–14688 (2020)R. Ahmed, M. G. Rosul, Y. Xu, M. Zebarjadi, G. Zangari. Electrochimica Acta, 368, 137554, (2021)A. Moysiadou, R. Koutsikou, M. Bouroushian. Materials Letters, 139, 112–115 (2015)D. Lippkow, H. H. Strehblow. Electrochimica Acta, 43, 14-15, 2131-2140, (1998)S. Thanikaikarasan, D. Dhanasekaran, K. Sankaranarayanan. Chinese Journal of Physics, 63, 138-148 (2020)

(Invited) Development of Single Crystal Nbn Superconductor on Wide Bandgap GaN By Sputtering and Thermal Annealing

The field of quantum computing is rapidly evolving, and Niobium Nitride (NbN) superconductors have emerged as a pivotal component in the field of quantum computing due to their unique properties. NbN possesses relatively higher superconducting transition temperature (Tc = 15-17 K) as compared to traditional superconductors, making it a promising material for various applications, including superconductor quantum computers, single photon detectors, and hot electron bolometers [1]. The investigation of NbN's superconductivity has been a subject of extensive research over the past few decades. Given that the properties of NbN are intricately linked to its crystal structure, lattice constant, and nitrogen content, precise control of the structural and electrical characteristics of NbN films is essential for the realization of NbN based quantum devices. The (111) planes of δ-NbN exhibit relatively small lattice mismatches with group-III nitride semiconductors (~0.2% for AlN and ~2.7% for GaN) [2], suggesting the potential for integrating crystalline NbN superconductors with nitride semiconductors on a single wafer. Notably, N-polar AlGaN/GaN high electron mobility transistors have been successfully fabricated on NbN films, operating under Tc with a negative differential resistance [3], indicating that the integration of nitride semiconductors and superconductors can be harnessed to create Josephson junctions. To achieve high-quality all-nitride NbN/group-III nitride/NbN Josephson junctions, a comprehensive understanding of the NbN/GaN heterointerfaces is crucial. Despite limited reports on the epitaxial growth of NbN films on nitride semiconductors, little is known about the structural and transport properties of such NbN films. Previously, MBE growth of NbN films have been demonstrated on GaN substrate, showing superconducting critical temperatures exceeding 10 K [4]. In this presentation, our efforts on the development of single crystal NbN thin films on wide bandgap GaN substrate using cost efficient sputtering technique followed by a subsequent high-temperature annealing will be presented. Commercially available single-crystalline GaN (0001)/sapphire templates as well as differently oriented (c and a-planes) sapphire substrates are used as the substrates for the sputtered deposition of NbN films at 20 °C. After the deposition, a high temperature annealing was performed separately at 950 °C for 30 mins under Ar as well as N2 atmosphere. While the as-deposited NbN film on GaN did not exhibit a discernible peak in the high-resolution XRD measurement, a high-intensity, single crystal (111)-oriented NbN film emerged prominently after annealing in both N2 and Ar environments. This suggests a notable enhancement in the crystalline quality of the superconducting material attributable to the thermal annealing process. Although the crystallinity of the NbN layer improves post-annealing, there is an associated increase in grain size and surface roughness. Preliminary findings indicate a reduction in the critical temperature of the NbN film from 12.82 K to 8.69 K after high-temperature annealing, potentially linked to the incorporation of impurities and crystallographic defects during this process. Further investigations using atomic resolution transmission electron microscopy, secondary ion mass spectrometry and X-ray photoelectron spectroscopy will be performed to investigate the influence of annealing duration, temperature, and conditions on the critical temperature, impurity incorporation and defect formation in NbN films deposited with different thickness.In continuation of our recent exploration into depositing crystalline superconducting NbN films on III-nitride semiconductors, this presentation will also focus on our recent advancement of ultrawide bandgap semiconductor materials such as the growth of high-quality quality β-Ga2O3 films and its ternary (AlxGa1-x)2O3 alloys, using metalorganic (MOCVD) and low-pressure (LPCVD) chemical vapor deposition growth techniques. Ga2O3 and (AlxGa1-x)2O3 have emerged as a promising semiconductor material platform for applications in high-power electronics and ultraviolet optoelectronics due to their excellent chemical and thermal stability, as well as high breakdown field strengths. The structural and electrical characteristics of Si-doped β-Ga2O3 and (AlxGa1-x)2O3 thin films will be presented. Additionally, we will present recent findings on achieving phase-pure β-(AlxGa1-x)2O3 films with a record-high Al composition (< 99%) [5]. Our research efforts into understanding the orientation-dependent Al incorporation in β-(AlxGa1-x)2O3 thin films and the determination of band offsets at β-(AlxGa1-x)2O3/β-Ga2O3 heterostructures will be presented. Furthermore, the presentation will touch upon the heteroepitaxial development of other phases of Ga2O3 and (AlxGa1-x)2O3, including α, γ, and κ. Acknowledgment: Dr. Bhuiyan acknowledges the support and guidance of his PhD advisor- Dr. Hongping Zhao at The Ohio State University for the MOCVD growth and characterization of β-Ga2O3 and (AlxGa1-x)2O3 films conducted in Zhao's group. Reference: Yamashita et al., Phys. Rev. Appl. 8, 054028 (2017).Kobayashi et al., Appl. Phys. Express 13, 061006 (2020).Yan et al., Nature 555, 183 (2018).G. Wright et al., APL Mater. 10, 051103 (2022).Bhuiyan et. al, Phys. Status Solidi RRL 17, 2300224 (2023). Figure 1

Suppressing interfacial nucleation competition through supersaturation regulation for enhanced perovskite film quality and scalability.

The growing interest in cost-effective and high-performing perovskite solar cells (PSCs) has driven extensive research. However, the challenge lies in upscaling PSCs while maintaining high performance. This study focuses on achieving uniform and compact perovskite films without pinholes and interfacial voids during upscaling from small PSCs to large-area modules. Competition in nucleation at concavities with various angles on rough-textured substrates during the gas-pumping drying process, coupled with different drying rates across the expansive film, aggravates these issues. Consequently, substrate roughness notably influences the deposition window of compact large-area perovskite films. We propose a supersaturation regulation approach aimed at achieving compact deposition of high-quality perovskite films over large areas. This involves introducing a rapid drying strategy to induce a high-supersaturation state, thereby equalizing nucleation across diverse concavities. This breakthrough enables the production of perovskite photovoltaics with high efficiencies of 25.58, 21.86, and 20.62% with aperture areas of 0.06, 29, and 1160 square centimeters, respectively.

Kinetics of Charge Reversal in the Double Layer Studied with an Electrochemical Quartz Crystal Microbalance (EQCM-D)

Normal pulse voltammetry on inert electrolytes was combined with a new electrochemical quartz crystal microbalance (EQCM) with millisecond time resolution, which allows to probe the kinetics of charge reversal in the diffuse double layer (DL) after a step in electrode potential. The QCM responds to the charge reversal because the local viscosity-density product depends on the type and the concentration of the ions. The time resolution was improved to 1 ms using multifrequency lockin amplification, which allows to study kinetic effects in dynamic electrochemistry, which were previously not accessible with gravimetry. The noise was lowered to less than 10 mHz by modulating the electrode potential and averaging Δf and ΔΓ over many modulation cycles.The overtone scaling was found to be the same as in gravimetry (-Δf/n » const. and ΔΓ/n < -Δf/n with n the overtone order), which, however, is not caused by a deposition of a rigid film in the Sauerbrey sense. A Sauerbrey-type QCM response is also caused by changes in Newtonian viscosity inside a layer with a thickness far below the penetration depth of the shear wave (such as the double layer).The frequency response in the electrolytes studied correlated well with the viscosity B-coefficients of the respective ions as employed in the Dole-Jones equation. The time constants inferred from gravimetry were similar to the time constants (the RC-times) from electrochemical impedance spectroscopy (EIS). There were small differences, which presumably go back to slow rearrangements inside the Helmholtz layer, which are not seen in EIS.The QCM response to double layer recharging in inert electrolytes is of great importance for the interpretation of QCM results on processes involving Faradayic charge transfer. Such a response is omnipresent as a background and might be misinterpreted as a gravimetric signal.[1] References[1] Leppin, C.; Peschel, A.; Meyer, F. S.; Langhoff, A.; Johannsmann, D. Kinetics of Viscoelasticity in the Electric Double Layer Following Steps in the Electrode Potential Studied by a Fast Electrochemical Quartz Crystal Microbalance (EQCM). Analyst 2021, 146 (7), 2160–2171. Caption: Shifts in frequency and bandwidth in response to potential steps (left). The gravimetric signal followed the steps with a delay of a few milliseconds. The amplitude and the response time depend on cation type (right). The counter ion was NO3 -. Both the amplitude and the response time correlate well with the viscosity B-coefficient. Figure 1

Porous Bismuth Vanadate Photoelectrodes for Solar Water Oxidation Reaction

Bismuth vanadate (BiVO4), a material known for its high visible light activity and good stability, is a promising candidate as a photoanode for overall water splitting [1]. Its performance is limited by its relatively short charge carrier diffusion length, which has recently been estimated to be ~15 nm [2]. For these kinds of photo-absorbers, commercial flat transparent conducting oxide (TCO) substrates are unsuitable since the thickness needed to absorb a sufficient amount of light far exceeds the carrier diffusion length. With this in mind, deposition of very thin semiconductor film onto the internal structure of (micro)porous, conducting substrates can ensure sufficient light absorption [3], whilst ensuring the individual film thickness is uniformly lower than the carrier diffusion length. Nanostructured TCO substrates can be fabricated using a convenient template-free technique called glancing angle deposition (GLAD). The glancing angle deposition method can be used to synthesize different variations of highly oriented submicron-sized pillars, ranging from vertical and tilted columns to zig-zag and helical structures with the help of shadowing effects and substrate rotation [4]. The optical and electrical properties of nanostructured TCO’s were found to depend on the type of material and the substrate temperature during deposition. We find that pillars made from tin-doped indium oxide show good conductivity (79 Ohm/sq) and are promising for the fabrication of nanostructured substrates for bismuth vanadate. A recently developed alternative approach is the use of transparent, porous, conducting substrates (TPCS) made from quartz felt, in which the quartz fibers are coated with F-doped SnO2 [5]. We found that a BiVO4 film thickness of 50 nm within these porous substrates is enough to absorb the same amount of light as a compact 400 nm bismuth vanadate film. We will discuss the deposition of BiVO4 into the TPCS substrates and the photoelectrochemical performance of these porous photoanodes.[1] K. Sivula and R. van de Krol, Nat. Rev. Mater. 1, 15010 (2016)[2] M. Schleuning, M. Kölbach, F. F. Abdi, K. Schwarzburg, M. Stolterfoht, R. Eichberger, R. van de Krol, D. Friedrich, H. Hempel, PRX Energy 1, 023008 (2022)[3] U. Björksten, J. Moser and M. Grätzel, Chem. Mater. 6, 858 (1994)[4] M. M. Hawkeye, M. T. Taschuk and M. J. Brett, “Glancing Angle Deposition of Thin Films”, John Wiley & Sons, Ltd., Chichester, UK (2014).[5] M. Caretti, E. Mensi, R.-A. Kessler, L. Lazouni, B. Goldman, L. Carbone, S. Nussbaum, R. A. Wells, H. Johnson, E. Rideau, J.-h. Yum, K. Sivula, Adv. Mater. 35, 2208740 (2023)

Stability in Photoluminescence and Photovoltaic Properties of Formamidinium Lead Iodide Quantum Dots

Formamidinium lead iodide (FAPI) thin films in the perovskite crystalline phase have piqued interest for single-junction solar cells due to their optimal bandgap, long photocarrier lifetime, and intrinsic structural stability. However, trap states on the surface and within the lattice impede the performance and stability of FAPI bulk crystalline film cells. Strategies such as film crystallization, deposition optimization, precursor engineering, and interface property tailoring aim to overcome these limitations. One approach involves forming FAPI quantum dots (QDs). By reducing the size, we achieve better quality and stable alpha-phase FAPI on a nanometer scale. In this contribution, we report synthesizing of alpha-phase FAPI QDs with a mean size distribution of 20 nm. These QDs exhibit a narrow photoluminescence emission peak at 1.61 eV and higher absolute quantum yields ranging from 70% to 86%. Compared to bulk FAPI with a 1.54 eV gap, a blue shift is observed due to the quantum confinement effect.However, achieving degradation-free perovskite solar cells under prolonged light soaking remains a challenge. Furthermore, we investigate the stability of FAPI bulk and QDS films in a humid chamber and after exposure to AM1.5G light in a humid setting (RH ~ 30%, T ~ 28°C). Our approach allows us to form homogeneously dispersed films of quantum dots with thicknesses of several hundred nanometers. These films are studied for photoluminescence and photovoltaic properties. Prototype solar cells incorporating synthesized FAPI QDs showed a power conversion efficiency of around 8%. These findings indicate considerably more stability in photoluminescence and photovoltaic properties of FAPI QDs for enhanced light-soaking stability compared to bulk FAPI films.

Immobilization of PCET Materials for Electrochemical pH Swing Driven Carbon Capture

Proton-coupled electron transfer (PCET) is a promising method in the realm of carbon capture and release mechanisms. Its fundamental capacity lies in electrochemically inducing pH swings within an aqueous solution, leveraging the high solubility of carbonates in highly alkaline water to capture CO2 and subsequently release iton demand when the aqueous solution is acidified. PCET-based methods promise higher energy efficiency for carbon capture compared to other electrochemical carbon capture methods because they feature fast charge transfer kinetics and can decouple gas-liquid contact and electrochemical activation. In theory, they also allow the use of cheap, widely available small-molecule PCET agents. However, in practice, PCET agents have shown a key limitation that has, thus far, hindered their scalability: oxygen-induced chemical degradation with continued electrochemical cycling. In this work we mitigate the prevailing issue of oxygen sensitivity by immobilizing PCET agents onto a fabric substrate. Via reactive vapor deposition (RVD), porous and conductive films composed of PEDOT-Cl and poly-aminoanthroquinone (PAAQ) are deposited on the surface of a wool felt blend fabric. This approach resulted in the development of a cost-effective, metal-free, and efficient electrode for both capture and release of CO2. Through electrochemical evaluation, the performance of PCET-active quinone moieties present on PAAQ was measured. The overall efficiency of electrochemical capture from gaseous CO2 was found to be 197 kJ/molCO2, substantiating the efficacy of this novel electrode. This work highlights the potential of fabric-immobilized PCET agents and presents a promising avenue towards a sustainable, efficient, and economically viable approach to carbon capture and release technologies.

Engineering Thin Films of Silicon Phthalocyanines for Organic Thin Film Transistors

Metal phthalocyanines (MPc) show great promise as semiconductors due to their exceptional optoelectronic properties, high thermal and photochemical stability, and ability to be easily synthesized and functionalized for specific applications. The metal/metalloid ion in the center of the MPc ring can significantly influence the electronic, optical, and magnetic properties of the compound, as well as its solubility and stability. The majority of MPc, such as copper phthalocyanine (CuPc) are used as hole-transport materials (p-type) in organic electronics. Silicon phthalocyanines (R2-SiPc) are emerging semiconductors which predominantly moves electrons and have led to high performance n-type organic thin-film transistors (OTFTs). Their low synthetic complexity paired with their versatile axial group facilitates the finetuning of their chemical properties, solution properties and processing characteristics without significantly affecting their frontier orbital levels or their absorption properties. The crystal engineering and film forming characteristics of R2-SiPc semiconductors can be tuned through appropriate axial group functionalization, therefore facilitating their integration into both OTFTs and OPVs by solution processing or vapor deposition.Our group has developed families of R2-SiPc and integrated them into OTFTs with an emphasis on thin film processing and engineering of the interfaces for improved device performance. We have established structure property relationships of the final device performance as a function of 1) R2-SiPc axial groups and peripheral groups, 2) surface chemistry and composition and 3) thin film deposition conditions. I will also be discussing our recent work using advanced film characterization such as polarized Raman microscopy and synchrotron based scanning transmission x-ray microscopy to evaluate the resulting films and optimize the OTFT performance. Figure 1