Perovskite Solar Cells: Spray Coating Commercial Readiness

Spray-coated perovskite solar cells are not yet in commercial modules, but they are the closest they have ever been, with pilot-line demonstrations and clear pathways to mass production emerging within the next few years. The technology has moved from lab-scale spin-coating to roll-to-roll compatible spray deposition, yet challenges in efficiency, stability, and defect control still prevent widespread commercial deployment.

Background: Why Perovskites and Why Spray Coating?

Perovskite solar cells have attracted intense research because they combine high power conversion efficiencies—now exceeding 26% in single-junction lab cells—with low-cost, solution-based manufacturing. Unlike silicon, which requires energy-intensive ingot growth and wafer sawing, perovskites can be deposited from liquid inks at low temperatures, potentially slashing manufacturing costs.

Spray coating is particularly attractive because it is a high-throughput, non-contact deposition method already used in industries like glass coating and automotive painting. It can be scaled to large areas using slot-die, ultrasonic, or airbrush spray systems, making it a natural fit for roll-to-roll production of flexible solar foils. The promise is a solar module that is lightweight, semi-transparent, and cheap enough to deploy on building facades, vehicle roofs, or even tents.

How Spray Coating Works for Perovskites

Spray coating involves dissolving perovskite precursors (typically lead halides and organic ammonium halides) in a solvent, then atomizing the solution into fine droplets that are deposited onto a substrate. The substrate moves under the spray nozzle, and the solvent evaporates, leaving a solid film. A subsequent annealing step crystallizes the perovskite.

Key parameters that must be controlled include:

• Solution concentration – affects film thickness and coverage.
• Spray rate and nozzle pressure – determines droplet size and deposition uniformity.
• Substrate temperature – influences solvent evaporation and crystallization.
• Ambient humidity – perovskites are hygroscopic and degrade in moisture.

Unlike spin-coating, which wastes most of the material and is limited to small areas, spray coating can deposit films over square meters. However, the trade-off is that spray films tend to be rougher and more prone to pinholes, which hurt efficiency and stability.

Current Efficiency and Stability Status

Lab-scale spin-coated perovskite cells have reached efficiencies above 26%, but spray-coated cells lag behind, typically achieving 18–22% for small-area devices. The gap comes from less uniform film morphology and higher defect densities. For modules, the efficiency drops further due to series resistance and inactive areas between cells.

Stability is the bigger hurdle. Perovskites degrade when exposed to moisture, oxygen, UV light, and heat. Encapsulation helps, but the materials themselves are intrinsically unstable. The best encapsulated perovskite modules have demonstrated operational lifetimes of several thousand hours, but silicon modules are warranted for 25–30 years. Perovskite-silicon tandem modules, where a perovskite layer is sprayed on top of a silicon cell, are a promising route because the silicon bottom cell provides stability and the perovskite adds efficiency.

Commercialization Efforts and Pilot Lines

Several companies and research consortia have built pilot lines for spray-coated perovskite modules. For example, a European consortium demonstrated a 200 mm × 200 mm module with 16% efficiency using slot-die coating, which is similar to spray in process complexity. Another startup has shown roll-to-roll spray-coated flexible modules with 12% efficiency on plastic substrates.

These efforts are still pre-commercial. The modules are not yet sold in large volumes, and the industry is waiting for a breakthrough in long-term stability. The U.S. Department of Energy’s Perovskite Startup Prize and similar initiatives have funded companies to accelerate commercialization, but no product has reached the mainstream market as of 2024.

Common Problems and Misconceptions

A common misconception is that spray coating is inherently inferior to spin-coating. In reality, with careful optimization of the spray parameters and post-deposition treatments, spray-coated films can approach the quality of spin-coated ones. The issue is reproducibility: spray coating is sensitive to environmental conditions, and small variations in temperature or humidity can cause defects.

Another problem is lead toxicity. Perovskites contain lead, which raises environmental and health concerns. While the lead is sequestered within the module, any damage or improper disposal could release it. Researchers are exploring lead-free alternatives like tin-based perovskites, but they are less efficient and even less stable.

Finally, the cost advantage of spray coating is not automatic. The perovskite material itself is cheap, but the encapsulation and electrode layers still dominate the cost. For spray coating to win, it must reduce the total module cost, not just the deposition step.

Comparing Spray Coating to Other Deposition Methods

• Spin-coating – best for lab research, but wastes >90% of the material and cannot scale beyond small areas.
• Slot-die coating – similar to spray but uses a continuous film of solution; better for uniform films, but requires precise gap control.
• Inkjet printing – allows digital patterning, but is slow and has nozzle clogging issues.
• Vapor deposition – produces high-quality films but requires vacuum equipment, increasing cost.

Spray coating sits between low-cost solution methods and high-quality vapor methods. It offers the best compromise for large-area, low-cost manufacturing, provided the film quality can be improved.

Cost and Manufacturing Scale-Up

The levelized cost of electricity (LCOE) for perovskite modules is projected to be lower than silicon, but only if manufacturing yields are high and lifetimes reach 15–20 years. Spray coating could enable module costs below $0.30/W, compared to ~$0.20/W for mature silicon, but the perovskite advantage is in building-integrated PV and tandem applications where silicon cannot compete.

Scale-up challenges include:

• Uniform deposition over large areas without defects.
• High-speed annealing to keep up with coating speeds.
• In-line quality control using optical or X-ray inspection.
• Recycling of solvents and lead waste.

Pilot lines are addressing these issues, but full-scale production lines have not been built yet.

Safety and Environmental Considerations

Handling lead halides requires proper protective equipment and ventilation. Spray coating generates aerosols that could be inhaled, so enclosed systems with filtration are necessary. The solvents used (e.g., dimethylformamide, DMSO) are toxic and flammable, requiring careful handling and disposal.

End-of-life recycling is not yet established for perovskite modules. Research is ongoing to recover lead and reuse the substrate, but no commercial recycling infrastructure exists.

Frequently Asked Questions

Are spray-coated perovskite solar cells commercially available?

No. As of 2024, no spray-coated perovskite modules are sold commercially. Several companies have pilot lines and demo products, but they are not yet mass-produced.

How efficient are spray-coated perovskite cells compared to silicon?

Lab-scale spray-coated cells reach 18–22%, while commercial silicon modules are 20–22%. Spray-coated modules are lower, around 12–16%, due to scaling losses.

What is the main barrier to commercialization?

Stability is the main barrier. Perovskites degrade in months, while silicon lasts decades. Encapsulation helps but does not fully solve the problem.

Can spray coating be used for tandem solar cells?

Yes. Spray coating is being developed for perovskite-on-silicon tandems, where the perovskite layer is sprayed on top of a silicon cell. This could boost efficiency above 30%.

Is lead in perovskites a safety concern?

Yes, lead is toxic. However, the lead is contained within the module, and research is exploring lead-free alternatives. Proper recycling and disposal are essential.

When will spray-coated perovskite modules be on the market?

Estimates range from 3 to 10 years, depending on stability improvements. Some analysts predict niche products like building-integrated PV within 5 years.

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