As an emerging photovoltaic technology, perovskite solar cells have attracted widespread attention due to their rapid improvement in photoelectric conversion efficiency. In the laboratory research and development stage, the preparation of perovskite functional layers (such as perovskite absorbing layers and transport layers) is a key link in determining battery performance. As a precision film preparation tool, the laboratory film coating machine can accurately control the film thickness, uniformity and crystal morphology during the solution film formation process, thus providing a reliable technical platform for studying the structure-activity relationship between material formulation, process parameters and final device properties.
Coating process principle
Laboratory coating machines usually work based on principles such as scraper coating or slit extrusion coating. At its core, it creates a uniform wet film on the substrate by precisely controlling the gap, movement speed, and solution supply between the coating head and the substrate, which is then subjected to subsequent drying and annealing to form a solid film. The process involves complex fluid dynamics versus dry crystallization kinetics.
The film formation quality is mainly affected by the following parameters: coating speed (V), scraper gap (H), solution concentration (C), solution viscosity (η), and substrate temperature (T). Wet film thickness (dwet) can be described approximately by formulas. For Newtonian fluids, in squeegee coating, the wet film thickness is related to the ratio of squeegee gap and coating speed, which can be simplified as:
dwet ≈ k · (h · vgap / v)α
where k is the constant related to the properties of the solution, α is the empirical index. Final dry film thickness (ddry) is closely related to the solid content of the solution: ddry = dwet · φ, where φ is the volume fraction of the solid content of the solution.
Perovskite thin film preparation
The film-forming process of perovskite precursor solutions directly affects the morphology, coverage and defect density of perovskite crystals. The application of laboratory film coating machine in this link needs to pay special attention to the following points:
First, perovskite solutions are sensitive to oxygen and moisture, so control of the coating environment, such as glove boxes or closed chambers, is critical. Secondly, the auxiliary crystallization steps (such as anti-solvent quenching, airflow purging, or substrate heating) immediately after coating need to be closely coordinated with the coating action, which puts forward requirements for the programmatic control ability of the coating machine. Finally, in order to obtain a uniform film over a large area, the design of the coating head (e.g., slit width, straightness) needs to be optimized to match the substrate size and ensure the flatness and temperature uniformity of the substrate platform.
Optimization of process parameters
By systematically adjusting the coating parameters, researchers can explore their impact on film properties and battery performance. The following example table illustrates a simplified set of study dimensions with more variables and repeated experiments.
| Coating speed adjustment range | Trend of influence on film morphology |
| Lower speed range | The thick wet film may increase the stress within the film and affect the crystallization uniformity |
| Medium speed range | It is conducive to the formation of a dense, full-coverage initial wet film |
| Higher speed range | The wet film becomes thinner, which may affect the final film thickness and coverage |
| Substrate temperature setting range | Trends of influence on drying crystallization kinetics |
| Lower temperature range | The solvent volatilizes slowly, the crystal growth time is prolonged, and the grain size may increase |
| Moderate temperature range | Balance volatilization and nucleation rate, often obtain a uniform dense film layer |
| Higher temperature range | Volatilizing too quickly can lead to pinholes or rough surfaces |
The optimization goal of these parameters is to obtain high-quality perovskite polycrystalline films with moderate grain size and small grain boundaries while ensuring that the film is highly uniform and has no pinholes, thereby increasing the open circuit voltage and filling factor of the battery.
The development and evaluation of laboratory coating process can refer to relevant general standards at home and abroad. For example, for film thickness measurement, reference can be made to standard methods based on optical interferometry or stylus profilers; For film uniformity evaluation, you can refer to standard test procedures for resistance or thickness distribution over large film surfaces. These standards provide a basic framework for process repeatability and data comparability.
Laboratory coating machines are indispensable tools in the study of perovskite battery materials and processes. It provides highly controllable and repeatable film preparation conditions to help researchers understand the film formation mechanism and accelerate the development of high-performance, high-stability perovskite modules. In the future, with the growth of demand for large-area preparation and roll-to-roll processes, the integration of coating technology with other online monitoring and rapid crystallization technologies will become an important development direction.