Precursor Films Research Articles

Instability of a Film Falling Down a Bounded Plate and Its Application to Structured Packing

The instability of a film falling down a vertical plate with lateral walls, which is the base configuration describing the structured packing geometry, is numerically investigated via the lubrication theory. The solid substrate wettability is imposed through the disjoining pressure, while the assumption of a tiny, precursor film thickness allows for modelling a moving contact line. Contact angles up to 60∘, which falls in the range of structured packing applications, are investigated, thanks to the full implementation of the capillary pressure instead of the small slope approximation. Parametric computations are run for a film falling down a vertical plate bounded by lateral walls, changing the plate width and the flow characteristics. An in-house, finite volume method (FVM) code, previously developed in FORTRAN language and validated in the case of film instability and rivulet flow, is used. The number of observed rivulets, triggered by the instability induced by the lateral walls, is traced for each computation. The numerical results suggest that rivulets with a given wavelength, equal to the one provided by the linear stability analysis, are generated, but only those characterized by a wavelength greater than a minimum threshold, which depends on the substrate wettability, induce partial dewetting of the domain. This allowed for the development of a simplified, statistically based model to predict the effective interface area and the rivulet holdup (required to estimate the mass transfer rate in absorption/distillation applications). Compared to the literature models of the structured packing hydrodynamics, which usually assume a continuous wetting layer, the influence of the flow pattern (continuous film or ensemble of rivulets) on the liquid holdup and on the interfacial area is introduced. The predicted flow regime is successfully verified with evidence from the literature, involving a flow down a corrugated sheet.

Fluid Control of Dip Coating for Efficient Large‐Area Organic Solar Cells

AbstractAs a classical low‐cost technique, dip coating has not been used for printable electronics. Here, the study demonstrates large‐area organic solar cells can be made by dip coating. The correlation is revealed among Van der Waals forces in precursor film, aggregation state of polymer, and fibrous orientation in active layer; the relationship is also expounded between fluid mechanics of the confined liquid in polymer scaffold and the continuity of the acceptor phase. By controlling the fluid characteristics, the ideal nanoscale bicontinuous interpenetrating network forms. As a result, the 1.0 cm2 rigid and 10.0 cm2 flexible cells exhibit efficiencies of 17.9% and 13.7%, respectively. Moreover, the method for predicting the optimal coating speed for the dip coating of given inks is proposed. Overall, this work not only demonstrates the superiority of dip coating for organic solar cell fabrication but also provides guidance for its application in printable electronics.

Tailoring selenization dynamics: How heating rate manipulates nucleation and growth boosts efficiency in kesterite solar cells.

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) has emerged as a promising photovoltaic material due to its low cost and high stability. The CZTSSe film for high-performance solar cells can be obtained by annealing the deposited CZTS precursor films with selenium (a process known as selenization). The design of the selenization process significantly affects the quality of the absorber layer. In this work, we systematically investigate the impact of heating rate on the selenization kinetics and the microstructural characteristics of the films using a two-step selenization method. The results indicate that a slow heating rate promotes surface crystallization, resulting in a thick and dense layer of large grains at the film surface that impedes the diffusion of Se vapor. Conversely, a rapid heating rate enhances the diffusion of Se into the interior of the film, synthesizing more low-melting-point intermediate compounds that facilitate grain growth and reduce the thickness of fine grains at the film bottom. Ultimately, a CZTSSe solar cell with an efficiency of 10.17% was fabricated at a heating rate of 200 °C/min. This research deepens the understanding of thin film growth mechanisms and advances the development of high-performance solar cells.

Fabrication of high-performance tin halide perovskite thin-film transistors via chemical solution-based composition engineering.

Metal halide perovskite semiconductors have attracted considerable attention because they enable the development of devices with exceptional optoelectronic and electronic properties via cost-effective and high-throughput chemical solution processes. However, challenges persist in the solution processing of perovskite films, including limited control over crystallization and the formation of defective deposits, leading to suboptimal device performance and reproducibility. Tin (Sn2+) halide perovskite holds promise for achieving high-performance thin-film transistors (TFTs) due to its intrinsic high hole mobility. Nevertheless, reliable production of high-quality Sn2+ perovskite films remains challenging due to the rapid crystallization compared with more extensively studied lead (Pb)-based materials. Recently, composition engineering has emerged as a mature and effective strategy for realizing the high-yield fabrication of Sn2+ halide perovskite thin films. This approach cannot only achieve improved TFT performance with high hole mobilities and current ratios1-6, but also enable reliable device operation with hysteresis-free character and long-term stability7-12. Here we provide the experimental procedure for precursor preparation, film and device fabrication and characterization. The entire process typically takes 20-24 h. This protocol requires a basic understanding of metal halide perovskites, perovskite film coating process, standard TFT fabrication and measurement techniques.

Promoting the grain growth of CZTSSe solar cells by incorporating Sb2Se3 and annealing in an atmosphere devoid of toxic selenium

Sb2Se3 was incorporated into precursor films. During annealing, Sb2Se3 decomposes, releasing Sb and Se, which provides the necessary energy for grain growth through mass transport at boundaries, thereby promoting the performance of solar cells.

Mechanisms of Phase Evolution in the Cu-Sb-S System Controlled by the Incorporation of Cu in Sb2S3 Thin Films.

Ongoing research in metal chalcogenide semiconductors aims to develop alternative materials for optoelectronic devices. However, due to cost and environmental considerations, there is an increasing emphasis on utilizing green materials. This shift toward sustainable materials and processing is expected to become essential in materials research. In this work, we report the microstructural evolution of thin films of the Cu-Sb-S (CAS) system. The films were obtained by annealing amorphous Sb2S3 precursor films previously immersed in a copper solution with variable residence time. Our main findings demonstrate that varying the residence time in immersion together with the annealing and crystallization of the precursor films leads to a controlled incorporation/distribution of Cu into the films, which promotes the formation of films with phases spanning from a mixture between Sb2S3 and CuSbS2 to a pure Cu12Sb4S13 phase, which represents a significant variation in optoelectronic properties. The phase transition mechanisms were investigated using first-principles calculations and correlated with the structural, morphological, and optoelectronic characterization. Results indicate that vacancies serve as nucleation sites for copper incorporation. Subsequently, interstitial sites are occupied during the phase transformation from Sb2S3 to CuSbS2, whereas the transition from CuSbS2 to Cu12Sb4S13 proceeds via a substitutional mechanism. This study contributes to understanding the fundamental phenomena underlying our proposed methodology. These results could promote the development of CAS-based semiconductors with predetermined properties by manipulating simple process parameters, such as the residence time in a copper solution.

An Effective Precursor‐Solutioned Strategy for Developing Cu2ZnSn(S, Se)4 Thin Film Toward High Efficiency Solar Cell

AbstractEnhancing the efficiency of Cu2ZnSn (S, Se)4 (CZTSSe) thin‐film solar cells requires the development of well‐crystallized light‐absorbing layers. A deep understanding of the role of precursor solution chemistry in film nucleation and crystal growth processes is essential. Insights into these processes enable the development of innovative strategies to enhance absorber quality, minimize detrimental bulk defects, and ultimately improve device performance. This study elucidates the condensation reactions between thiourea and metal cations, as well as the alcoholysis of 2‐methoxyethanol (MOE), at different concentrations of precursor solutions. The primary focus of this study is implementing a simple and environmentally friendly innovative spin‐coating strategy, aimed at optimizing Cu2ZnSnS4 (CZTS) precursor films and adjusting the Se content within the film bulk to promote grain growth during selenization. This strategy effectively improves absorber morphology while suppressing the formation of deep‐level defects, thereby enhancing carrier transport in both interfacial and bulk regions of the absorber layer. Consequently, CZTSSe absorbers with enhanced crystallinity and reduced defects are synthesized, resulting in a solar cell with an impressive efficiency of 14.10%. These findings underscore the potential for creating highly efficient kesterite CZTSSe solar cells through the manipulation of precursor solution chemistry using environmentally friendly solvents.

Influence of Copper and Tin Oxidation States on the Phase Evolution of Solution-Processed Ag-Alloyed CZTS Photovoltaic Absorbers

Kesterite-based semiconductors, particularly copper–zinc–tin–sulfide (CZTS), have garnered considerable attention as potential absorber layers in thin-film solar cells because of their abundance, nontoxicity, and cost-effectiveness. In this study, we explored the synthesis of Ag-alloyed CZTS (ACZTS) materials via the sol–gel method and deposited them on a transparent fluorine-doped tin oxide (FTO) back electrode. A key challenge is the selection and manipulation of metal–salt precursors, with a particular focus on the oxidation states of copper (Cu) and tin (Sn) ions. Two distinct protocols, varying the oxidation states of the Cu and Sn ions, were employed to synthesize the ACZTS materials. The transfer from the solution to the precursor film was analyzed, followed by annealing at different temperatures under a sulfur atmosphere to investigate the behavior and growth of these materials during the final stage of annealing. Our results show that the precursor transformation from solution to film is highly sensitive to the oxidation states of these metal ions, significantly influencing the chemical reactions during sol–gel synthesis and subsequent annealing. Furthermore, the formation pathway of the kesterite phase at elevated temperatures differs between the two protocols. Structural, morphological, and optical properties were characterized via X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Our findings highlight the critical role of the Cu and Sn oxidation states in the formation of high-quality kesterite materials. Additionally, we studied a novel approach for controlling the synthesis and phase evolution of kesterite materials via molecular inks, which could provide new opportunities for enhancing the efficiency of thin-film solar cells.

Solar Cells Manufactured Using Concentrated Solar Energy Toward Carbon Neutralization

AbstractThe high photoelectric conversion efficiency (PCE) of solar cells and their environmentally friendly, low‐carbon manufacturing processes are crucial for advancing carbon neutrality goals. This study introduces Fresnel lenses to focus sunlight for the sintering of mesoporous titanium dioxide (m‐TiO2) layers as an innovative method for fabricating perovskite solar cells (PSCs), effectively circumventing the energy‐intensive and carbon‐emitting high‐temperature furnace sintering traditionally required. Through this concentrated solar annealing technique, an efficient and eco‐friendly sintering of the m‐TiO2 layer is successfully achieved by removing organic residues from the precursor film and enhancing the film's transmittance, electrical conductivity, and grain size. Consequently, this has led to improved coverage of the perovskite layer and enhanced overall photovoltaic performance of the solar cells. Experimental results indicate that the m‐TiO2 film subjected to 60 min of concentrated sunlight sintering (CSS) demonstrates optimal photovoltaic performance, with the fabricated compact‐layer‐free PSCs achieving an impressive photoelectric conversion efficiency of up to 17.69%. This research not only offers a novel, cost‐effective approach for the sustainable production of PSCs but also contributes tangible solutions for the green transformation of the photovoltaic industry and the achievement of carbon neutrality. This work points the way toward using solar energy to prepare solar power generation devices.

Chloride Engineering for Boosting Perovskite Photovoltaics: Impact on Precursor Coordination, Crystallization, and Film Quality.

Perovskite solar cells (PSCs) have seen rapid advancements over the past decade, driven by their exceptional optoelectronic properties and high power conversion efficiencies. Cl-based additives strategy has significantly contributed to these advancements by enhancing crystallinity, improving preferred orientation, and optimizing the surface morphology of perovskite films. This review provides a comprehensive summary of recent advancements and insights into the critical role of Cl-based additives in perovskite photovoltaics, focusing on the mechanisms behind Cl incorporation and its effects on film and device performance. First, the impact of Cl on precursor solution coordination and colloidal characteristics is discussed. Then, how Cl-based additives influence the phase transitions of perovskites, including methylammonium lead iodide (MAPbI3), formamidinium lead iodide (FAPbI3), and 2D perovskites is examined. Furthermore, the impact of Cl-based interfacial treatments on perovskite film quality is explored. Based on these insights, the overall impact of Cl treatments is also reviewed on the properties of perovskite films. Finally, a brief overview of the remaining challenges and future perspectives are provided to guide ongoing research efforts toward optimizing Cl additive engineering for high-performance PSCs.

Facile synthesis and antibacterial performance of novel biofilms based on bacterial cellulose from jackfruit rags, incorporating polyvinyl alcohol, Ag nanoparticles, and Eclipta prostrata extract

The advancements of antibacterial biofilms have received much attention in biomedical, wound healing, and food packaging. Here, we developed a novel bacterial cellulose (BC) through Acetobacter xylinum strains using jackfruit rags as a carbon source, under different fermentation conditions. The highest BC production of 5.668 g L–1 of dried weight BC was obtained from the medium with 1: 2 (w v–1) of jackfruit rags/water ratio, 4.5 initial pH and 9 days of incubation. Further bacterial cellulose was incorporated into mixture of polyvinyl alcohol (PVA), biogenic silver nanoparticles (AgNPs) and Eclipta prostrata extract (EPE) to develop antimicrobial films. The micromorphology, mechanical, and functionality of BC/PVA/AgNPs/EPE biofilms were compared with those of BC/PVA, BC/PVA/EPE, BC/PVA/AgNPs film precursors. The results showed that mechanical strength of BC/PVA/AgNPs/EPE biofilms increased, while their water vapor permeability significantly decreased. Fourier transform infrared and scanning electron microscopy revealed excellent compatibility between AgNPs, EPE and the BC/PVA matrix. The BC/PVA/AgNPs/EPE biofilm had strong antibacterial performance against Escherichia coli and Staphylococcus aureus, as the average zone of inhibitions were 18.5 ± 0.33 mm and 21.0 ± 0.3 mm, respectively. These outcomes suggest that the BC/PVA/AgNPs/EPE biofilm can be a good candidate for antibacterial food packaging.

Perovskite Film Passivation and Precursor Engineering for High Performance Devices

Perovskite films are attracting much attention due to their excellent optoelectronic properties. The corresponding photovoltaic devices have shown a record efficiency of 26.7% since 2009, which is very promising to surpass silicon solar cells. The defects of the perovskite films are the major negative factors in achieving high efficiency. The defects of the perovskite films are related to the polycrystal nature of the perovskite films, which is unavoided and caused by the solution-based method. Therefore, high-quality perovskite films with fewer defects are very critical to obtain high-efficiency devices. One strategy is to passivate defects of the films after the film fabrication. We passivate perovskite films with organic materials including polymers, organic small molecules as well as dye molecules. The organic molecules with the special organic functional groups interact with perovskite films to modify the defects of the films to improve the charge transport and reduce charge recombination, leading to improved device performance. The surface defects and the grain boundary defects of the perovskite films are passivated by the organic materials, which is confirmed by the electron/hole-only devices, electronic impedance spectroscopy (EIS) studies, photoluminescence, and time-resolved photoluminescence. The device efficiency increases significantly which is manifested by the J-V measurements. The passivation mechanism of the devices by organic materials is investigated and demonstrated. In addition, The other strategy is to incorporate some additives into the perovskite solutions to adjust the perovskite film growth toward fewer defects. We control the perovskite film growth process by precursor engineering via solvent and solute control. High-quality perovskite films can be obtained by our method for high-performance devices.

Synthesis and Structural Modulation of Nanoporous Copper Films by Magnetron Sputtering and One-Step Dealloying.

Nanoporous copper (np-Cu) has attracted much more attention due to its lower cost compared to other noble metals and high functionality in practical use. Herein, Al100-xCux(x = 13-88 at.%) precursor films with thicknesses of 0.16-1.1 μm were fabricated by varying magnetron co-sputtering parameters. Subsequently, utilizing a one-step dealloying strategy, a series of np-Cu films with ligament sizes ranging from 11.4-19.0 nm were synthesized. The effects of precursor composition and substrate temperature on the microstructure of np-Cu films were investigated. As the atomic ratio of Cu increases from 15 to 34, the np-Cu film detached from the substrate gradually transforms into a bi-continuous ligament-channel structure that is well bonded to the substrate. Furthermore, the novel bi-layer hierarchical np-Cu films were successfully prepared based on single-layer nanoporous films. Our findings not only contribute to the systematic understanding of the modification of the morphology and structure of np-Cu films but also offer a valuable framework for the design and fabrication of other non-noble nanoporous metals with tailored properties.

Rapid activation of a solution-processed aluminum oxide gate dielectric through intense pulsed light irradiation.

In this study, we report rapid activation of a solution-processed aluminum oxide gate dielectric film to reduce its processing time under ambient atmosphere. Aluminum precursor films were exposed to a high energy light-pulse and completely converted into dielectric films within 30 seconds (450 pulses). The aluminum oxide gate dielectric film irradiated using intense pulsed light with 450 pulses exhibits a smooth surface and a leakage current density of less than 10-8 A cm-2 at 2 MV cm-1. Moreover, dielectric constants of the aluminum oxide layer were calculated to be approximately 7. Finally, we fabricated a solution-processed indium gallium zinc oxide thin-film transistor with AlO x using intense pulsed light irradiation, exhibiting a field-effect mobility of 2.99 cm2 V-1 s-1, threshold voltage of 0.73 V, subthreshold swing of 180 mV per decade and I on/I off ratio of 3.9 × 106.

Addressing the Apparent Controversies Between the Contact Angle-Based Models for Estimation of Surface Free Energy: A Critical Review

The most popular contact angle (CA)-based approaches for determination of solid surface free energy (SFE) are considered: (i) single liquid methods, mainly of Neumann and Chibowski, (ii) the multiple liquids approach of Owens–Wendt–Rabel–Kaelble (OWRK), and (iii) van Oss-Chaudhury–Good (vOCG) acid–base model. Evaluations based on Neumann and Chibowski models agree between each other. Under the assumption of equilibrium “wet wetting” (i.e., presence of saturated precursor film ahead of the drop), the model of Chibowski transforms in Lipatov’s interfacial equilibrium rule, i.e., the Antonow rule derived for the ternary point solid–liquid–gas. Very good agreement is observed between single and multiple liquids models where OWRK/vOCG values can be viewed as a mean of the individual SFE adopted by the solid with each of the wetting probes. Both approaches (single and multiple liquids) can be used in conjunction to evaluate SFE dispersion and polar components and to elucidate hydrophobicity and hydrophilicity. The implementation of apparently fully non-polar liquids (diiodomethane, bromonaphthalene) in OWRK and vOCG is practically and theoretically suspect. CA-based estimates represent apparent SFE determined by the interactions of both the solid surface and the probing liquid, which are very useful to elucidate the energy, chemistry and dynamics of the solid surface.

Sub-ambient water wettability of hydrophilic and hydrophobic SiO2 surfaces.

The wettability of SiO2 surfaces, crucial for understanding the phase transition processes of water, remains a topic of significant controversy in the literature due to uncertainties in experiments. Molecular dynamics (MD) simulations offer a promising avenue for elucidating these complexities, yet studies specifically addressing water contact angles on hydrophilic and hydrophobic SiO2 surfaces at sub-ambient temperatures are notably absent. In this study, we experimentally measured water contact angles of hydrophilic and hydrophobic SiO2 surfaces at ambient temperature and employed MD to investigate water contact angles on Q3, Q3/Q4, and Q4 SiO2 surfaces across temperatures ranging from 220 to 300K. We investigated the effects of the distribution of hydroxyl groups, droplet size, and hydroxyl density and found that the hydroxyl density had the largest impact on contact angle. Moreover, hydrogen bond analysis uncovered enhanced water affinities of Q3 and Q3/Q4 SiO2 surfaces at lower temperatures, and the spreading rate of precursor films reduced with decreasing temperature. This comprehensive study sheds light on the intricate interaction between surface properties and water behavior, promoting our understanding of the wettability of SiO2 surfaces.

Achieving over 10 % efficiency in kesterite solar cells via selenium-free annealing

The unsatisfactory crystalline quality of the absorber layer has seriously impeded the development of kesterite photovoltaic devices, including a small grain size, a typical multi-layer structure, and inherent defects and defect clusters. Herein, we simultaneously modify the nature of the absorber bulk and the heterojunction interface by sputtering quaternary alloy targets and subsequent selenium-free annealing to improve the photovoltaic performance of Cu2ZnSnSe4 (CZTSe) solar cells. By adjusting the sputtering power, the elemental content and distribution in the precursor film are effectively controlled, which helps to obtain a single-layer large grain CZTSe absorber layer with better homogenization and compactness. The harmful inherent defects are significantly suppressed by such a modification. Simultaneously, the widened depletion width and enhanced built-in electric field, as well as improved band alignment at the heterojunction, enhance carrier collection. As a consequence, the efficiency of CZTSe solar cells has improved greatly from 6.91 % to 10.12 %. The single-target preparation strategy without selenization provides a simple and novel perspective for simultaneously adjusting the morphology and defects of kesterite photovoltaic materials, paving the way for promoting innovative industrial applications.

Impact of Tetrakis(dimethylamido)tin(IV) Degradation on Atomic Layer Deposition of Tin Oxide Films and Perovskite Solar Cells.

Tin oxide (SnOx) films synthesized by atomic layer deposition (ALD) are widely explored in a range of optoelectronic devices including electrochemical sensors, transistors, and photovoltaics. However, the integrity of the key ALD-SnOx precursor, namely tetrakis(dimethylamido)tin (IV) (TDMASn), and its influence on the properties of ultimate films remain unexplored. Here a significant degradation of TDMASn into bis(dimethylamido)tin(II) via the Sn-imine complex is reported, and its impact on the corresponding films and devices is examined. It is found, surprisingly, that this degradation does not affect the growth kinetics and morphology of ALD-SnOx films. But it notably deteriorates their electronic properties, resulting in films with twice the electrical resistance due to different oxidation mechanisms of the degradation products. Perovskite solar cells employing such films exhibit a significant loss in power conversion efficiency, primarily due to charge transport and transfer losses. These findings urge strategies to stabilize TDMASn, a critical precursor for ALD-SnOx films, or to identify alternative materials to achieve efficient and reliable devices.

Compact Layer‐Free Perovskite Solar Cells with Low‐Temperature UVO Photochemical Annealed Mesoporous TiO2 Layers

In recent years, the field of perovskite solar cells (PSCs) has seen rapid development, with most high‐efficiency devices incorporating dense titanium dioxide (TiO2) barrier layers and mesoporous TiO2 layers to enhance selective electron transport. However, the manufacturing process requires high‐temperature sintering steps above 450 °C, leading to significant energy consumption. In addition, this requirement greatly limits the potential applications of PSCs in the field of flexible electronics. This study introduces a new method for preparing dense‐layer‐free mesoporous PSCs using low‐temperature UVO annealing of m‐TiO2. UVO annealing effectively removes residual organic components from m‐TiO2 precursor films, enhances the conductivity and wettability of the films, thereby reducing carrier recombination and improving the performance of PSCs. Research has shown that PSC with a 40 min UVO annealed m‐TiO2 layer exhibits a final photoelectric conversion efficiency of 17.79%, comparable to devices with traditional high‐temperature annealed m‐TiO2 PSCs. In addition, after 7 days at room temperature and ambient humidity, the unpackaged device maintains a maximum conversion efficiency of 84%. These findings indicate that UVO light annealing is a feasible alternative to high‐temperature annealing, providing a simpler, more cost‐effective, and energy‐saving method for the preparation of metal oxide electron transport layer in PSCs.

An atomic-level insight in the transition from non-reactive to reactive wetting using molecular dynamics simulation

The intrinsic mechanisms that differentiate between non-reactive wetting and reactive wetting are still unclear. In this work, we have compared reactive and non-reactive wetting systems and made an attempt to explain the factors that contribute to the differences between these systems. In this aspect, we modeled five distinct wetting systems with different levels of reactivity between liquid Al droplet and solid Ni substrates. Results show that interfacial reactions during the reactive wetting cause a local increase of the temperature, a change in the droplet properties such as surface tension and self-diffusion, and in the overall substrate composition. This has led to a lower final contact angle and faster spreading rate, both of which point towards improved wettability due to the interfacial reactions. On the other hand, non-reactive wetting is dominated and controlled through the formation of a precursor film on the substrate. On tuning the reactivity, it was revealed that a competition between dissolution and precursor formation occurs where the former is more dominant with increasing reactivity. This study should aid in a better understanding of the wetting process and the atomic-level mechanism controlling the spreading behavior.