Perovskite solar cells offer a promising pathway to low-cost, high-efficiency photovoltaics due to their desirable properties: low exciton binding energies, long charge-carrier diffusion lengths, and high absorption coefficients. Their solution processability further enhances their economic potential. While spin-coating is a prevalent deposition method, solvent engineering using antisolvents plays a crucial role in achieving high-quality perovskite films. Previous research highlighted the impact of antisolvent dripping time on film formation, revealing complex dynamics influenced by solvent-antisolvent interactions. However, a comprehensive understanding of the role of various antisolvents and their application parameters remained elusive. Contradictory results regarding optimal antisolvent properties (polarity, boiling point) and application parameters (volume, temperature, dripping delay) were reported. This study aimed to address this knowledge gap by systematically investigating the effect of antisolvent application rate on the performance of perovskite solar cells fabricated with a diverse range of antisolvents.

The literature extensively documents the solvent engineering method for perovskite film deposition, emphasizing the importance of the antisolvent application step. Studies have investigated various parameters such as antisolvent dripping time, volume, temperature, and the use of additives. However, inconsistencies exist regarding the optimal conditions, with reports varying widely across different antisolvents. Some studies favored cold antisolvent treatments, while others reported better results with elevated temperatures. The choice of antisolvent itself also appears arbitrary, with successful devices fabricated using both polar and nonpolar solvents, and with widely varying boiling points. This lack of consistency highlights the need for a deeper understanding of the underlying mechanisms governing antisolvent-assisted perovskite film formation.

The researchers fabricated nearly 800 triple-cation Cs0.05(MA0.17FA0.83)0.95Pb(I0.9Br0.1)3 perovskite solar cells using 14 different antisolvents. A simple method was employed to control the duration of antisolvent application by using micropipettes of different sizes (250 µL and 1000 µL) to dispense the same volume (200 µL) of antisolvent at varying rates. This resulted in 'fast' (Δt = 0.18 s) and 'slow' (Δt = 1.3 s) antisolvent application times. The device architecture was glass/ITO/PTAA/PFN-Br/perovskite/PCBM/BCP/Ag. The perovskite layer was deposited via spin-coating followed by antisolvent treatment. Detailed characterization techniques were employed, including scanning electron microscopy (SEM) to analyze film morphology, X-ray diffraction (XRD) to determine crystal structure and orientation, and X-ray photoelectron spectroscopy (XPS) to determine surface composition. Photovoltaic performance was evaluated by measuring current-voltage (J-V) curves under simulated AM 1.5 illumination. To investigate the role of precursor solubility and miscibility, the researchers tested the solubility and miscibility of methylammonium iodide (MAI) and formamidinium iodide (FAI) in each antisolvent using a 4:1 DMF:DMSO solution. The effects of varying the antisolvent application rate, volume, temperature, and fabrication environment (dry air vs. N2 glovebox) on the photovoltaic performance were also examined. Finally, the impact of precursor stoichiometry variations on device performance was investigated by altering the amount of organic precursors in the perovskite solution, keeping the Pb concentration constant. The range of x value in Cs0.05(FA0.83MA0.17)0.95xPb(I0.9Br0.1)3 was varied from 0.9 to 1.1.

The study revealed a clear categorization of the 14 antisolvents into three types based on their optimal application rate for achieving high PCEs. Type I antisolvents (alcohol series) performed better with fast application, while Type III antisolvents (aromatics) yielded superior results with slow application. Type II antisolvents showed little sensitivity to application rate. The key factors determining antisolvent type were the solubility of organic precursors in the antisolvent and its miscibility with the host solvent. Type I antisolvents exhibited high solubility for organic precursors, leading to their removal during slow application and resulting in poor film quality. Type III antisolvents showed immiscibility with the host solvent, leading to incomplete perovskite conversion during fast application. Type II antisolvents displayed a balance of low precursor solubility and good miscibility, resulting in consistent performance regardless of application rate. Microscopic analysis revealed that the optimal application rate for each antisolvent type resulted in dense, compact perovskite films with minimal PbI2 residue and large, well-connected grains. The study also demonstrated that by using the optimal antisolvent application procedure, high-efficiency devices (PCE >20%) could be fabricated even with a broad range of precursor stoichiometries. Specifically, devices with both excess and deficiency of organic iodides (up to ±6%) showed high efficiency, thus negating the commonly used PbI2 excess.

The findings provide a fundamental understanding of the antisolvent-assisted perovskite film formation process. The classification of antisolvents based on their solubility and miscibility with the precursor solution allows for a predictive approach to optimize perovskite solar cell fabrication. The ability to achieve high-efficiency devices across a range of precursor stoichiometries simplifies the fabrication process and improves reproducibility. The observed differences in microstructure and photovoltaic performance underscore the critical role of careful control over antisolvent application parameters. The results suggest that the common practice of using excess PbI2 might not stem from inherent efficiency benefits, but rather from enhanced reproducibility across different fabrication conditions and researcher variability in antisolvent application rate. This study eliminates the need for excess PbI2, improving both efficiency and stability.

This research demonstrates a general approach to achieve high-efficiency perovskite solar cells using any antisolvent, controlled by the application rate. The identification of key factors governing perovskite film quality simplifies fabrication and improves reproducibility. Future research could focus on expanding this methodology to other perovskite compositions and exploring scalable fabrication techniques for large-area devices.

The study focused on a specific triple-cation perovskite composition. While the applicability to other compositions was partially explored, more comprehensive investigations are needed to confirm broader applicability. The impact of long-term stability under various environmental conditions requires further investigation. Finally, while large-area fabrication was tested on 5x5 cm² substrates, scaling to larger industrial sizes requires further optimization.