Perovskites I (Part b)
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Use the link below to share a full-text version of this article with your friends and colleagues. Learn more. The phase analysis using spectral techniques indicate good thermochemical compatibility between HA and CaTiO 3. In vitro cell culture studies using L mouse fibroblast and SaOS2 human osteoblast cell lines provide clear evidence of cell adhesion, spreading, and proliferation as well as the formation of cellular bridges, and, hence, good in vitro biocompatibility of the developed composite can be realized.
Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries other than missing content should be directed to the corresponding author for the article. Volume 95B , Issue 2. The full text of this article hosted at iucr. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. If the address matches an existing account you will receive an email with instructions to retrieve your username. Bikramjit Basu Corresponding Author E-mail address: bikram iitk.
The precursor solution was filtered by a 0. The core of this experimental set up is a spray-coating machine Holmarc, Opto-Mechatronics Pvt. The atomizing gas at a pressure of 0. To fabricate the active layer thin film, mixed-halide perovskite, PbCl 2 , and MAI solutions were pre-loaded into the syringe pumps and injected sequentially through capillaries 0. The same ultrasonic transducer used for post treatment of spun-on PEDOT:PSS was employed as the substrate holder and the ultrasonic vibration provider during the spray-coating process.
The temperature of the syringe pumps and the surface of ultrasonic transducer were both controlled by a temperature controller. The speed and distance of nozzle tip to the substrate, the flow rate of each solution, the time interval between two sprays, and the process duration were controlled by software. The process variables listed in the tables have been determined to provide a molar ratio of MAI to PbCl 2 reagents.
Operating conditions and characteristics of perovskite films fabricated by single-step and sequential 2S-SVASC spray methods. In order to elucidate the importance of the sequential spraying, we performed two experimental runs 9 m and 10 m based on the conventional one-step spraying, with and without imposed ultrasonic vibration on the substrate. The structural characteristics and performance of the prepared thin films were compared with the perovskite thin films prepared via the 2S-SVASC method.
A good coordination between the solvent and solute causes a uniform deposition and high surface coverage [ 20 ]. However, complete removal of DMSO needs prolonged annealing times at elevated temperatures, making the perovskite susceptible to decomposition. Using pure DMF also leads to a very fast chemical reaction in a few seconds after contact between reagents has been made.
This immediate conversion results in rapid and irregular crystallization and unfavorable chemical conversion, coverage, and morphology. The PCBM precursor solution was loaded into a syringe and sprayed through a 0. A nm back contact Al was thermally evaporated outside of the glovebox. Scanning electron microscopy SEM, Hitachi, Model SN, Japan was used to study the surface and cross-sectional morphology of the fabricated thin films and device.
The optical mode of this machine was utilized to observe the surface topography. Electrical conductivity of spun-on PEDOT:PSS films was measured via the 4-point probe measurement technique, along a mm straight line on each sample. Coverage values were measured visually through a simple color contrast difference analysis, using ImageJ The surface quality and the electrical properties are significantly improved when a spun wet film is treated by ultrasonic vibration using SVPT.
The effect of the imposed substrate vibration on the nanostructure of spun-on PEDOT:PSS thin films has been studied in detail in our previous work [ 37 ]. Also, under controlled conditions, imposing low power vibration can promote mixing and stability of the film [ 36 ]. Increased evaporation as a result of vibration can also cure the film faster and before pinholes formation. This improvement in transparency is due to a better uniformity and a thinner and smoother film formed c.
According to the surface topography and morphology images Fig. The effects of the substrate temperature on the film structure of spray-on PEDOT: PSS films were investigated in our previous reports [ 33 , 35 , 36 ], where it was inferred that spraying on a high temperature substrate results in the formation of numerous defects and pinholes on the PEDOT:PSS film due to the fast evaporation, bubble formation, and poor droplet spreading and coalescence. Therefore, the two-step sequential substrate vibration-assisted spray coating 2S-SVASC was employed for the fabrication of perovskite films to suppress the above-mentioned drawbacks.
As illustrated in Fig. The large roughness can be attributed to the ribbon- or filament-like features.
Lead-free hybrid perovskites for photovoltaics
Such crystallites present colorless or pale yellow color, a signature of monohydrated and di-hydrated perovskite phases [ 38 , 39 ]. In the following, we explain the effect of the hydration on perovskite morphology and crystal growth and the effect of the substrate temperature on this phenomenon. Incorporation of water into the perovskite lattice results in disordering of 3D networks to 1D needle-type and 0D amorphous features.
H 2 O forms a metastable thin and colorless needle-type feature [ 38 ]. This is a reversible process occurring during film drying in dark and vacuum [ 38 ]. In highly prolonged exposure to humid media, an irreversible reaction occurs as follows, which is associated with discoloring to an opaque yellow color, a signature of PbI 2 crystals [ 38 , 39 ]. A hydrated perovskite specimen may contain both mono- and di-hydrated phases, as well as some decomposed parts that contain PbI 2 [ 38 , 39 ].
It has been shown that the irreversible perovskite decomposition to PbI 2 can only happen by water condensation on perovskite surface, resulted from a temperature difference between the film surface and the humid air [ 38 ].
In the current work, the substrate temperature is much higher than the ambient temperature. It is therefore assumed that condensation never occurs during deposition, but partial condensation may take place during the sample analysis. The H 2 O produced in di-hydration reaction R1 may transform the remaining perovskite phase. On the basis of this simple theory, we can recognize that the thin film made at run 1 has undergone a complete hydration path based on reactions R1 and R2, leaving different rod-like, grainy, and amorphous regions on the surface, while in thin films formed at runs 2—3, the monohydrated phase occupies a bigger part.
This interesting evolution resulted from the effect of different TISs. We reiterate that in our sequential method, the PbCl 2 precursor solution is sprayed in the first step and the MAI solution is sprayed in the second step. The films are seemingly composed of grainy or spiky crystallites, whose size and density significantly changes by the TIS. On the other hand, the hydration is an exothermic thermo-phobic reaction which can be suppressed in high temperature conditions.
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It is, therefore, proposed that the perovskite thin films deposited on a hot substrate are relatively stable against hydration during the deposition process. The change in density and crystal size due to a change in the TIS can be again due to the effect of the solvent content. Reduction of the normal boiling point of the solvents causes faster and more uniform crystallization, while better wettability favors droplet spreading and coalescence and surface coverage, consequently [ 22 , 40 ].
Lead-free hybrid perovskites for photovoltaics
It is worth mentioning that unlike the literature reports, we recognized that no crystal sintering occurs at high temperature deposition. We ascribe this advantage to the imposed ultrasonic vibration prohibiting crystals aggregation [ 32 , 35 ]. In sequential deposition, the form and quality of the precursor PbCl 2 thin film strikingly determines the final form and quality of the perovskite thin film.
Burschk et al. This preserving of size and morphology is only accessible with sequential deposition into a porous template, such as mesoporous TiO 2.
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But in a flat substrate, as in the planar architecture, the deposited PbCl 2 acts as a template as well as a reagent for the formation of perovskite. We observed that a smaller, denser, and more uniform PbCl 2 thin film helps the creation of a more uniform, smooth, and intact perovskite thin film. Following the above discussion on the importance of the morphology of the PbCl 2 film on the final morphology of the perovskite film, we studied the structure of PbCl 2 thin films sprayed on an ultrasonically vibrating substrate in Fig.
The PbCl 2 thin films shown in Fig. The PbCl 2 deposited on low temperature substrate Fig. The 1D orientation of crystal growth in Fig. Deposition of PbCl 2 on the high temperature substrate Fig. High surface coverage and low roughness are achieved owing to imposed ultrasonic vibration during nucleation and crystal growth. The fabrication conditions of PbCl 2 films are the same as those of runs 1—3 for a and runs 4—6 for b , and TIS is irrelevant in this case. Having discussed the formation of the PbCl 2 films Fig. The PbCl 2 crystal lattice serves as a template for the formation of the target compound, i.
The configuration of the organic cations between these layers is controlled by the strong inter-layer chemical bonding and the weak van der Waals forces between them. This scenario is well consistent with the condition of runs 2 and 3 and particularly with the condition of runs 5 and 6, in which PbCl 2 crystals are completely formed long TIS before the MAI solution is sprayed atop. The absence of voids in the perovskite films in runs 5 and 6, compared to the precursor PbCl 2 thin film, implies reorganization of PbCl 2 and MAI due to the intensive diffusion during the film growth [ 5 ].
The main advantage of our 2S-SVASC deposition approach compared with the state-of-the-art methods for deposition of perovskite films is the application of the imposed ultrasonic vibration on the substrate and its combination with spray coating, which makes it a controllable scalable method. To study the effect of power amplitude of the imposed vibration, Fig.
In Fig. These results suggest that in a given frequency, there is a threshold vibration power beyond which the ultrasonic vibration causes film rupture and dewetting. This threshold depends on the physical and interfacial properties of the precursor solution [ 36 ] and needs to be addressed for each individual system. Run 9 m has been performed by co-spray using the conditions of run 7, performed by sequential sprays, and run 10 m has been performed by co-spray, using the conditions of run 6, performed by sequential sprays. In order to examine the merit of the two-step sequential method, in which two perovskite precursors are sequentially sprayed, perovskite films were also fabricated by one-step co-spray deposition of a mixture of the two precursor solutions on stationary run 9 m and vibrating substrates run 10 m.
Perovskites I Part B - E. Burzo Hardcover
When the substrate is vibrated Fig. SEM of run 10 m is lower than the sample sequentially sprayed c. SEM of run 6. This is because in co-spraying approach, due to the strong interaction between DMSO and IPA, the reagents partially precipitate upon mixing. This early crystallization disturbs the balance of molar ratio between PbCl 2 and MAI reagents in the liquid phase. Therefore, the precursor solution after mixing consists of a sintered solid phase and a dilute liquid phase, which should be essentially filtrated before spraying. The resultant filtrate will be a dilute bright yellow solution, leaving behind a thin layer with low coverage due to the lack of sufficient reagents.
Therefore, a combination of sequential spraying and substrate vibration through the 2S-SVASC renders the best perovskite film characteristics. The reference graphs were adopted from the literature [ 21 , 25 , 38 , 41 , 42 ]. Comparing with the literature, the best perovskite thin films were obtained in runs 5 and 6 Fig. In contrast to the single-halide structure, this iodide-chloride mixed formulation is rather stable, and, therefore, amenable with ambient processing. The absence of the PbCl 2 peaks in perovskite patterns implies a complete transformation of PbCl 2 precursor, and the absence of typical signals of PbI 2 at Product Details.
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