“Adv. Energy Mater.” Aerosol-Jet-Assisted Growth of CH3NH3PbI3 Perovskite Thin Films: A Method for Fabricating High-Quality, Defect-Free Films for Efficient Solar Cells
Product Introduction
Equipment Parameters
I. Core Research Summary
- Automated preparation of the air environment: No inert glovebox is required; thin-film deposition can be performed in 30% humidity air. The entire process is fully programmable, eliminating the limitations of manual spin-coating and significantly improving device‑to‑device performance reproducibility.
- Precise grain control, elimination of impurity residues: By employing a nanoporous PbI₂ substrate together with a NaI ink additive, and optimizing the atomization and sheath‑gas flow rates, we have fabricated micron‑scale, continuous perovskite grains free of voids. XRD analysis reveals no extraneous PbI₂ peaks, and carrier lifetimes are significantly extended. The optimized planar p‑i‑n solar cell achieves a power conversion efficiency (PCE) of 15.4% and a fill factor (FF) as high as 76%.
- Pioneering direct printing of perovskites on curved surfaces: Leveraging a 2–10 mm adjustable printing gap and a three-axis coordinated motion platform, the active layer is directly printed onto a hemispherical PET substrate; after flattening, the cell efficiency reaches 5.4%, demonstrating the capability to fabricate 3D‑shaped substrates.
- Universal and Scalable Process: The complete deposition workflow is compatible with various perovskite architectures and transport-layer inks, and can be extended to all‑aerosol‑printed photovoltaics, photodetectors, and flexible light‑emitting devices.
II. Core Operating Principle and Unique Advantages of Aerosol Spraying
(1) Complete Workflow
- Ultrasonic atomization: High-frequency ultrasound breaks down the precursor ink, generating ultrafine droplets measuring 1–2 μm; a nitrogen carrier gas transports the aerosol to the printing nozzle.
- Coaxial sheath gas focusing: A annular protective gas flow compresses the aerosol plume, and the nozzle–substrate gap is adjustable between 2 and 10 mm, preventing nozzle clogging.
- Programmatic Deposition: XY/Z three-axis CAD‑defined paths, with layered printing of two types of precursors—PbI₂ and MAI.
- Fog‑solid reaction: MA‑based aerosol droplets penetrate the solid PbI₂ layer, triggering an in situ solid–fog–solid phase reaction that yields perovskite; gentle annealing then completes crystallization.
(2) Major advantages compared to spin coating, slot-die coating, and inkjet printing
- Non-contact + Curved Surface Compatibility : It does not require direct contact with the substrate, enabling uniform film deposition on textured, hemispherical, and flexible curved surfaces, whereas spin coating is limited to flat, rigid substrates.
- No nozzle clogging : The sheath‑gas encapsulates the ink jet, addressing the pain points of inkjet printing—nozzle clogging due to drying and the inability to sustain long‑term mass production.
- The ink exhibits a broad viscosity compatibility range, requires only minimal consumables, and achieves significantly higher material utilization compared to spin coating.
- Fully automated digital fabrication, eliminating the need for masks, enables precise printing of micrometer-scale photovoltaic pixels.
- Fog‑solid conversion replaces liquid–liquid contact, reducing solvent dissolution and pinhole defects in the intermediate phase, thereby yielding a higher‑purity thin film.
III. Key Technological Innovations
Innovation 1: A Novel Fog–Solid-Phase Perovskite Crystallization Mechanism
Innovation 2: Substrate Structure–Grain Growth Matching
Innovation 3: NaI additive induces ultra-large, pore-free grains
Innovation 4: Precise dual-airflow parameter control over the degree of film conversion.
Innovation 5: Integrated 3D curved-surface printing with three-axis simultaneous motion
IV. Core Process Challenges and Corresponding Solutions
Challenge 1: Imbalance in atomized gas flow and incomplete film conversion, leading to pinholes.
Problem: When the atomization flow rate is too low, the MA supply is insufficient, leaving a large amount of unreacted PbI₂ on the film; when the atomization flow rate is too high, the droplets coalesce and dissolve the substrate, resulting in extensive porosity.
✅ Breakthrough: By confining the current density to a moderate range and integrating a nano‑porous PbI₂ substrate, ion diffusion efficiency is enhanced, striking a balance between conversion efficiency and film integrity.
Challenge 2: High-humidity air conditions readily induce perovskite decomposition.
Problem: In conventional solution‑based fabrication, films prepared in ambient air are prone to water absorption and degradation, resulting in yellowing of the film and a sharp drop in efficiency.
✅ Breakthrough: By using an IPA/DMF‑based MA ink formulation, the atomization and deposition process is significantly shortened. Combined with a 70°C substrate temperature control and relative humidity below 30%, high‑quality thin films can be stably fabricated.
Challenge 3: The dense PbI₂ substrate features fine grains, leading to severe charge recombination.
Problem: The dense lead iodide layer has few pores, making it difficult for MA droplets to penetrate deeply; the perovskite grain size is relatively small, leading to severe carrier recombination and resulting in low open-circuit voltage and current.
✅ Breakthrough: By extending the natural drying time of the PbI₂ thin film, a porous precursor film is prepared, enhancing droplet penetration depth and increasing grain size.
Challenge 4: Non-uniform film thickness and significant efficiency degradation in curved-surface printing.
Problem: The distance between the curved surface and the nozzle varies across different areas, resulting in inconsistent droplet deposition and significant variations in film thickness.
✅ Breaks through the limitations of three-axis simultaneous motion by automatically compensating for Z-axis height, maintaining a stable printing gap of 2–10 mm throughout the process and ensuring uniform mist‑beam coverage on curved surfaces.
Challenge 5: Traditional processes rely on manual operations, resulting in poor device repeatability.
Problem: Even slight variations in spin-coating speed and annealing time can significantly affect battery performance, resulting in high efficiency variability across a batch of 50 cells.
✅ Breaks new ground with fully automated CAD‑controlled management of airflow, speed, and print passes; standardizes process parameters, achieves an extremely narrow device‑to‑device performance spread, and significantly enhances production‑line stability.
V. Future Application Scenarios of Aerosol-Deposited Perovskites
- Wearable flexible photovoltaics
- Architecture / Photovoltaic Systems for Irregular-Shaped Aerospace Structures
- Miniature Embedded Self-Powered Device
- Large-scale roll-to-roll mass-production line
- Expansion of Multifunctional Optoelectronic Devices
Figure 1. a) Simplified schematic of the core components of the aerosol jet (AJ) printer used for perovskite thin-film deposition in this study. Key parameters optimized in this work include the ink formulation, atomizer flow rate, and sheath‑flow velocity. b) Schematic illustrating the fabrication process for forming CH3NH3PbI3 perovskite films within a p‑i‑n planar heterojunction device architecture. c) Time‑dependent sequence of the current AJ operation. d) Relative motion of the AJ print head with respect to the substrate, enabling the creation of rectangular perovskite “pixels” of predefined dimensions. The patterning was achieved using a nozzle with a diameter of 150 µm at a fixed platen temperature.
Figure 2. a) Top-view SEM images of 350-nm perovskite films with a dense lead iodide layer, grown on glass/ITO/PEDOT:PSS substrates under different AJ printing conditions. The films were annealed together with DMF vapor at 100°C for 80 minutes after printing. Scale bars in all images are 2 µm. b) Digital photographs of the corresponding CH3NH3PbI3 films printed on 1-inch × 1-inch square substrates. c) Comparison of XRD patterns of the AJ-printed films.
Figure 3. a) UV–vis absorption spectra of AJ-printed perovskite films prepared under the conditions shown in Figure 2 (black line: SFR = 5; red line: SFR = 15; green line: SFR = 25; blue line: SFR = 35; all flow rates are in sccm). At higher atomization flow rates (i.e., 25 sccm), the film becomes discontinuous, leading to an uneven distribution of light absorption within the film (dashed lines indicate measurements taken from different regions of the sample). b) Dense lead iodide layer and c) nanoporous lead iodide layer: three-dimensional evolution of UV–vis absorbance as a function of AFR and SFR (at a wavelength of 720 nm). All flow rates are in sccm, and absorbance values are expressed in O.D.
Figure 4. Schematic illustration of perovskite formation and thin-film morphology evolution under different AFR (air flow ratio) and SFR (surface flow ratio) conditions during aerosol jet printing.
Figure 5. Top-view SEM images of a 350 nm perovskite film prepared on a glass/ITO/PEDOT:PSS substrate using a nanoporous lead iodide layer under different AJ printing conditions. The scale bar in all images is 2 µm.
Figure 6. a) Top-view SEM image of an AJ-printed perovskite film fabricated on a glass/ITO/PEDOT:PSS substrate, with a nanoporous lead iodide layer; the CH3NH3I ink was supplemented with 2 mol% sodium iodide. b) Representative XRD pattern of one of these films.
Figure 7. a) Device architecture of planar heterojunction solar cells investigated in this study; b) Optimal J–V characteristics of perovskite layers fabricated via defect‑mitigation (AJ printing), using CH3NH3I ink with or without sodium iodide additive: hollow circles denote forward scans, solid circles denote reverse scans; c) Performance distributions of spin‑coated (SC) and AJ‑printed perovskite solar cells, with and without sodium iodide additive; Gaussian fits to the histograms for each device type are superimposed on the same plot.
Figure 8. a) Schematic illustration of the direct printing process of perovskite semiconductors onto the hemispherical surface during aerosol jet printing; b) Photographs of lead iodide and c) CH3NH3PbI3 printed by AJ, deposited on the PET/ITO/PEDOT:PSS surface attached to the hemispherical substrate; d) J–V characteristics of a perovskite solar cell fabricated with an active layer directly printed onto the hemispherical surface, employing a PHJ device architecture based on PET/ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/C60/Al.
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