Antisolvent‐Enhanced Crystallization of Luminescent All‐Green Organic–Inorganic Manganese‐Halide Films Deposited by Aerosol‐Assisted Chemical Vapor Deposition Technique on Either Glass or Elastomer Substrates

The in situ deposition of emerging organic–inorganic metal halides (OIMHs) films on glass or stretchable substrates has been challenging, and no methodology has been reported to achieve this goal. The aerosol‐assisted chemical vapor deposition technique using an antisolvent‐enhanced crystallization process (AEC–AACVD) is a simple, cost‐effective, scalable, and high‐throughput technique operated under ambient atmosphere and pressure. The AEC–AACVD technique (an all‐green chemistry methodology) is used in this work to deposit TPA2MnCl2Br2 luminescent films on glass and highly stretchable elastomer substrates. The effect of using different antisolvents on the structural, morphological, and photoluminescent (PL) characteristics of films deposited on glass is reported. It is found that the intensity of the characteristic green emission peaks at 511 nm for this OIMH, improving with the antisolvent application. The TPA2MnCl2Br2 films deposited using a mixture of antisolvents result in the maximum emission intensity when deposited on stretchable substrates, maintaining their overall PL characteristics. The processability, scalability, and performance reported here for these films prove their potential application in the next generation of OIMH‐based optoelectronic technologies.

Aerosol-assisted chemical vapor deposition (AACVD) is a simple, cost-effective, scalable, and high-throughput method operated under ambient atmosphere and pressure.This powerful technique relies on the nebulization of precursor solutions (generation of air-suspended micron-sized precursor solution droplets) to be transported by a carrier gas to the hot substrate's surface.As the precursor droplet approaches the substrate, it undergoes a temperature gradient that evaporates the solvent, leaving behind highly reactive species that heterogeneously nucleate and grow on the substrate as films.
The AACVD method has been employed extensively to deposit metal chalcogenides and oxides, such as ZnS and ZnO. [21,22]ecently, this technique has been adapted for the deposition of metal organics and metal halides based on Pb, [23,24] Sn, [25] and Cu. [26]Furthermore, AACVD offers exceptional versatility as the possibility of substituting highly toxic solvents for green solvents such as water to deposit lead-halide perovskites, and the appealing multisource capacity for transport simultaneously either precursor solutions, additives, or antisolvents from separate sources, enhancing the nucleation rate and increasing the processing window.The careful selection of the solvent-antisolvent system is critical for achieving highquality metal-halide film coatings, thus ensuring optimal device performance.In recent years, incorporating an antisolvent into the film deposition process has been recognized as one of the most effective means to widen the processing window and achieve highly uniform metal-halide films.However, a significant challenge has been the toxicity of many commonly used antisolvents, such as chlorobenzene, methylbenzene, and toluene, posing a major obstacle to potential commercialization. [27]ome slightly polar, environmentally friendly antisolvents like propan-2-ol and propan-2-one have been explored, but they have the drawback of dissolving a certain quantity of ions during the deposition process. [28,29]Additionally, less polar green antisolvents like ethyl acetate have been investigated, but their low boiling points lead to rapid crystallization, resulting in lower-quality films. [30]Antisolvent engineering by mixing antisolvents has become a method to address the need for more precise control over the crystallization process.This approach enhances film properties compared to single antisolvents. [31,32]ere, a methodology is presented for depositing all-green TPA 2 MnCl 2 Br 2 (TPA = tetrapropylammonium) luminescent films on glass substrates.In the simultaneous transportation of nebulized methanolic precursor solutions and green antisolvents, the green chemistry processing route principles and antisolvent engineering by mixing were adopted in AEC-AACVD to increase the deposition rate and modulate the structural quality of the films.Moreover, the versatility of this methodology was tested by depositing the luminescent film on top of an elastomer substrate, which could pave the way for the fabrication of OIMHs-based elastic devices.The approach reported here is attractive for developing OIMH optoelectronic technologies due to the possibility of being deposited from solution at low manufacturing costs and using abundant, nontoxic precursor materials and green solvents over nonconventional substrates.

Glass Substrate
All the films studied displayed a bright green emission when exposed to UV light (365 nm).However, the luminescence intensity of the films is dependent on the solvent system used, observable by the naked eye. Figure 1a shows a digital photograph of the green-emitting M4 film under 365 nm UV-light emitting diode (LED) (5 W) excitation.Steady-state photoluminescence (PL) spectroscopy was employed to explore the luminescence properties of the films further.Figure 1b shows the room-temperature PL excitation and emission characteristics of the films.Two groups of bands constitute the excitation spectra, the most intense in the 250-300 nm range and the rest in the 340-400 nm range.The transition associated with each band is also indicated in Figure 1b.The strong interaction between their d electrons and ligands determines the optical properties of the Mn 2þ OIMHs.The electronic configuration of the 3d 5 energy level is sensitive to local perturbations when coordinated with halogens or organic ligands.Thus, the PL emission color of manganese in OIMHs systems is in the red-orange range for octahedral geometry in the six-coordinated configuration and the green region for a tetrahedral in a four-coordinated configuration.In the green-emitting TPA 2 MnCl 2 Br 2 films, the emission band originates from the 4 T 1 ! 6A 1 transition in the [MnX 4 ] À2 (X = Cl, Br) tetrahedron. [33]he intensity of the luminescence bands exhibited by the films was dependent on the antisolvent employed with the lower intensity for films deposited without antisolvent (M0), indicating that all the antisolvent systems chosen for this study helped to improve the luminescence of the resulting films to some extent.Figure 1c plots the normalized integrated emission intensity (area under the PL curve) for all films studied (see Experimental Section).A lower impact on the luminescence intensity was observed when propan-2-one (M1) and ethyl acetate (M2) were used, followed by propan-2-ol (M3) and the solvent mixture (M4) that propitiated a fourfold and a sixfold enhancement, respectively, compared with the M0 film.Figure 1d shows the normalized emission PL spectra, and it exhibits that the emission band of all the films peaks at 511 nm and has a full width at half medium of 50 nm, and no changes in the shape of the emission spectra were detected upon normalization.The PL decay curves of the films are plotted in Figure 1e, which describes the same decay dynamics for all the samples.The curves were fitted with a single exponential function, and an average decay time of 599 μs was calculated.
To precisely characterize the emission color observed, the Commission Internationale de L'Eclairage chromaticity coordinate for this green emission was calculated as 0.17399 and 0.64817 based on the luminescence spectrum of the M4 film (Figure 1f ).
In Figure 2a, the X-ray diffraction (XRD) patterns of the films show features which is consistent with the TPA 2 MnCl 4 diffractogram simulated from CIF data.Additional peaks at 2θ = 30.6°areassociated with the TPA-X (X = Cl, Br) phase.This peak intensity also depends on the antisolvent, suggesting a phase modulation effect during deposition.Figure 2b shows the diffraction peaks associated with the (1 0 1) and (3 1 À1) diffraction planes for the samples M0, M3, and M4, along with the simulated pattern for the TPA 2 MnCl 4 and TPA 2 MnBr 4 .For both planes, the positions of the diffraction peaks of the samples lie between the respective simulated peaks for the Cl-and Br-only compounds, according to a mixed halide phase.
Contact profilometry measurements examined the surface topography of the films, and the results are plotted in   To further understand the effect of the antisolvent on the growth of the OIMHs films, the surface morphology of the five films deposited using different antisolvent systems was characterized by scanning electron microscopy.For each film, the top-view micrographs under three different magnifications and a cross-sectional (CS) scanning electron microscope (SEM) image are presented in Figure 3a-e.
No substrate is exposed at lower magnifications for the film deposited without antisolvent assistance (Figure 3a), indicating a good film coverage over the entire deposition area through a layer-by-layer type of growth.However, some bumps popping from the surface are observed, consistent with the height profile obtained from profilometry measurements.At higher magnifications (Â2500 and Â5000), a surficial decoration by spheroidal particles of %250 nm diameter is observed.These particles appear to be generated by methanol that partially redissolves nearby grains associated with the TPA-X phase detected in XRD analysis.CS-SEM reveals that the thickness of the film is about 2 μm.Considering that the only solvent involved in the deposition of the film deposited using no antisolvent is methanol, the poor crystallinity, decreased thickness, and surficial decoration of the film indicate a slow nucleation rate that competes with a redissolution process during deposition since methanol is a suitable solvent for the TPA 2 MnX 4 structure.The function of the antisolvents is to supersaturate the OIMHs precursor droplets as they arrive at the hot surface substrates and to extract the residual "good solvent" from the film, further enhancing crystallization.
The film deposited using propan-2-one as antisolvent in Figure 3b showed some large voids ranging from 3-10 μm.Such large pinholes could be attributed to antisolvents' effectivity in enhancing crystallization without extracting the solvent.In this scenario, the surface has been crystallized with the solvent trapped inside the bulk and opens pores when released.Higher magnifications show some grain boundaries and cracks generated by solvent evaporation.The wrinkled surface is also decorated with TPA-X particles shown as bright domains.
The ethyl acetate-assisted film (Figure 3c) exhibited highly discontinuous domains with large voids, low compactness, and a rough top surface that could be caused by residual solvent accompanied by fast crystallization.Such poor film quality has been observed in metal-halide films with low substrate wettability, [34] indicating that ethyl acetate promotes the OIHM crystallization but decreases the nucleation rate in the glass substrate.The CS micrograph shows that the discontinuity of the film across the thickness and the poor adhesion to the glass substrate cause mechanical delamination at the interface.
By employing propan-2-ol as antisolvent, smoother films with improved coverage were deposited, as depicted in Figure 3d.The surface is highly decorated by the TPA-X particles evenly distributed over the entire film surface, consistent with the intense diffraction peak at 30.7°observed in Figure 2a.CS-SEM image reveals a uniform thickness along the film (%5 μm) with a coarsening grain layer structure in which the grain boundary was difficult to discern.
When the antisolvent mixture was utilized, a homogeneous film free of pinholes was observed (Figure 3e).At higher magnifications, the contour of OIMnH appears as interconnected grains on the film surface.The grain surface is wrinkled, resembling the effect of propan-2-one.However, only a small amount of the TPA-X secondary phase was observed, in good agreement with XRD results.The side view of the film shows multigrain domains across the layer structure; the thickness was estimated as %6 μm. Figure 3f,g shows the atomic force microscopy (AFM) images of the M0 and M4 films, respectively.The bumps observed in Figure 3f for the film deposited without antisolvent assistance (M0) are in good agreement with SEM observations and exhibited an average surface roughness of approximately 131 nm.
In contrast, when the solvent mixture (M4) was utilized, the average surface roughness decreased to around 39 nm.The rapid volatilization of methanol and the redissolution of the film during deposition in the absence of antisolvent assistance resulted in a higher degree of surface roughness.In contrast, using the solvent mixture contributed to a reduced surface roughness and, consequently, a smoother surface.This improvement is attributed to optimizing properties such as boiling point, vapor pressure, polarity, and dielectric constant when combining solvents, which enhances the nucleation and growth of the deposited film.
It is hypothesized that the changes in PL intensity between the films deposited using different antisolvent systems are related to many factors, such as thickness, crystalline quality, phase purity, compactness, and surface texturization.

Stretchable Elastomer Substrate
Elastic devices have attracted tremendous attention nowadays for their enhanced mechanical properties under deformation, foldability, and conformability as electronic skin for motion and healthcare monitoring applications. [35]However, the substrate's surface chemistry and metal-halide precursors interplay is crucial for film nucleation and growth in spin-coating and evaporation techniques. [36]Therefore, the low wettability of elastomer substrates makes their use as elastic substrates for metal-halide films challenging.Based on the previous observations, an attempt to deposit a TPA 2 MnCl 2 Br 2 film on top of a highly stretchable elastomer (VHB 4910, 3 M, VHB = very high bond) substrate by AEC-AACVD was made as a proof of concept.Employing the antisolvent mixture (used before for the M4 film), a highly luminescent OIMnH film deposition was possible.In contrast, film growth failed when no antisolvent was used.Figure 4a-c shows digital photographs of the film deposited on top of the elastic substrate (labeled as M4E) under UV-LED irradiation (365 nm, 10 W).The relaxed substrate is 25 mm Â 25 mm, and the luminescent properties of the films were maintained upon stretching at %150% (Figure 4b) and at %400% (Figure 4c), maintaining its luminescence properties.The normalized PL excitation and emission of the film were then compared with that of the M4 film and plotted in Figure 4d.The emission band of the M4E film, centered at 511 nm, corresponds to the same 4 T 1 ! 6A 1 Mn transition observed in the glass-supported films.In the excitation spectrum, the same bands observed in the glass-supported film are present.Nevertheless, the relative intensity of the low-energy group of bands between 350 and 400 nm increases dramatically.It has been reported that the shape of the excitation spectrum of manganese-based phosphors is highly influenced by electronphonon coupling. [37]More detailed studies are needed in the future to understand how the substrate affects the excitation features as observed.
SEM image of the M4E film shows a noncontinuous film composed of microstructured arrays of perovskite islands robustly adhered to the substrate surface (Figure 4e).In the AEC-AACVD process, the liquid precursor microdroplets undergo temperature gradient as they approach the hot substrate's surface, critically increasing the supersaturation concentration, followed by heterogeneous nucleation in which the number of nucleation sites vary with substrate surface chemistry and can be enhanced by an antisolvent.According to the theory, the number of nucleation sites depends on the interplay between supersaturation (ξ) and interface free energy (G), yielding three types of film growth after solvent evaporation: Frank-van der Merwe (layer-by-layer growth), Volmer-Weber (island growth), and Stranski-Krastanov (layer plus island growth). [38]The increased island size observed in the M4E film evidences the decreased nucleation rate of the OIMHs on the VHB polymer surface, compared with the layer-by-layer type of growth observed on glass substrates in which the nucleation process is enhanced.Finally, the chemical structure of the M4E film was studied by XRD and presented in Figure 4f.The XRD pattern is composed of the contribution of both the amorphous substrate and the crystalline TPA 2 MnCl 2 Br 2 component, demonstrating that AEC-AACVD is a great candidate for the deposition of OIMHs materials on substrates with low nucleation rate characteristics.
The results from this work suggest that the great versatility of the AACVD methodology will pave a new path for the deposition of OIMHs films for diverse applications in optoelectronic devices.By solvent engineering for antisolvent-enhanced crystallization, new possibilities for exploring emerging materials as films over nonconventional substrates are now open.

Conclusions
A simple, robust, and highly versatile AEC-AACVD method for depositing TPA 2 MnCl 2 Br 2 luminescent films on glass and flexible substrates is presented here.The precursor salts were nebulized and fed from a single methanolic solution, and the crystallization rate was controlled using different antisolvents during film deposition.All the films deposited on glass substrates presented the characteristic green emission, centered at 511 nm, associated with the 4 T 1 ! 6A 1 transition of Mn 2þ in tetrahedral coordination geometry and the same decay time dynamics.Using and mixing different antisolvents enhanced the nucleation, deposition rate, and PL of films deposited on glass substrates.The antisolvent-enhanced deposition method was optimized with a mixture of antisolvents, and it was used to grow TPA 2 MnCl 2 Br 2 luminescent films onto VHB elastic substrate.We believe that by exploring more antisolvent mixtures and additives, the processing window can be expanded and extrapolated to other OIMHs family members for their integration into functional optoelectronic devices.
Solutions Preparation: For all the films, the precursor solution was prepared by dissolving MnCl 2 •4H 2 O (1 mMol, 1.979 g) and TPA-Br (2 mMol, 5.331 g) in methanol (100 mL) under ambient air conditions and stirred magnetically for 1 h at room temperature.
AACVD Process Description: The home-built computer numerical control (CNC)-controlled AACVD system functioned within an enclosed plexiglass box filled with ambient air.A detailed description of the system can be found elsewhere. [26]The configuration employed in this system was a double-source setup.Specifically, methanol served as the solvent, while propan-2-one, ethyl acetate, propan-2-ol, and a mixture of the three antisolvents (1:1:1 vol%) were utilized as antisolvents, all within the realm of green chemistry.The precursor solution and the chosen antisolvent were simultaneously atomized to generate micron-sized precursor droplets suspended in air.These droplets were then conveyed to the nozzle chamber by a flow of N 2 gas injected into each flask at a rate of 4.5 LPM.An auxiliary N 2 gas flux with a flow rate of 4.5 LPM was introduced directly into the nozzle chamber to achieve two objectives: a) preventing coalescence of the mixed precursor droplets by diluting them and b) accelerating the droplets toward the hot substrate.As the droplets approached the surface of the substrate, a gradual evaporation of the solvents occurred, followed by nucleation and growth.Nonreacted residuals were extracted by an outer tube and safely evacuated to a fume hood.The inner nozzle used in the process had a circular CS with a diameter of 25 mm.The distance between the nozzle and the substrate was set at 0.8 mm, and the nozzle was moved across the substrate at a speed of 5 mm s À1 .The total deposition time for the process was 600 s, and the substrate temperature was maintained at 80 °C.After the deposition, all the films were stored under ambient conditions and characterized without further postdeposition treatments.
The process of depositing the OIMnH films involved using different antisolvents, and each resulting film was given a specific label based on the antisolvent utilized.The film deposited without the assistance of any antisolvent was referred to as "M0".In contrast, the films deposited using different antisolvents, such as propan-2-one, ethyl acetate, and propan-2-ol, were labeled as "M1", "M2", and "M3", respectively.A film was also deposited using a mixture of the aforementioned antisolvent in equal volumetric quantities labeled "M4".Additionally, the same methodology employed for the deposition of the film labeled "M4" was also used to deposit an elastomer-supported film, which was designated as "M4E".
Characterization: XRD patterns were collected using a D500 Siemens diffractometer.A Leica-Cambridge Stereoscan 440 SEM was used to assess the morphology of the films.AFM analysis was performed using a Park Scientific Autoprobe CP instrument in the contact mode.Profilometry measurements were performed using a KLA Tencor D-100 profilometer under applied force = 0.2 mg.PL emission, excitation, and decay times were acquired with an FS5 spectrofluorometer from Edinburgh Instruments, and data for PL quantum yield calculations was obtained in the same instrument equipped with an integrating sphere.Digital photographs were taken by irradiating the films with a UV LED (365 nm, 10 W) under ambient atmosphere and illumination.

Figure 1 .
Figure 1.a) Digital micrograph of the film deposited using the antisolvent mixture assistance (M4) irradiated by UV light.b) Photoluminescence (PL) excitation and emission spectra of the films and c) integrated PL emission.d) Normalized PL emission spectra, e) decay time curves, and f ) Commision Internationale de L'Eclairage diagram of the films.(e) shows the fit to a single exponential decay.

Figure 2c .
Figure 2c.The films' mean thicknesses were estimated as 1.962, 4.022, 2.052, 4.417, and 5.966 μm for the M0, M1, M2, M3, and M4, respectively.To further understand the effect of the antisolvent on the growth of the OIMHs films, the surface morphology of the five films deposited using different antisolvent systems was characterized by scanning electron microscopy.For each film, the top-view micrographs under three different magnifications and a cross-sectional (CS) scanning electron microscope (SEM) image are presented in Figure3a-e.No substrate is exposed at lower magnifications for the film deposited without antisolvent assistance (Figure3a), indicating a good film coverage over the entire deposition area through a

Figure 4 .
Figure 4. a) Digital photographs of the TPA 2 MnCl 2 Br 2 film deposited onto VHB 4910 elastic substrate excited by 365 nm light irradiation under relaxed condition, b) stretched at 150% and c) 400% conditions.d) Normalized PL excitation and emission spectra of the film deposited on VHB 4910 and glass substrates.e) SEM image and f ) XRD pattern of the VHB-supported film obtained under a relaxed condition.