Building-integrated photovoltaics (BIPV), including technologies like luminescent solar concentrators (LSCs), are important for achieving sustainable energy goals in the building sector. LSCs typically utilize glass windows containing luminescent materials to absorb sunlight and guide it to solar cells at the window edges. Yet, conventional LSCs have drawbacks like restricted efficiency, material breakdown over time, high costs, and potential safety concerns with certain materials. Complex manufacturing processes also impede large-area application.  

A New Method: Laser-Nanostructured Glass

Researchers at Aalto University have presented a promising substitute: using femtosecond-laser-nanostructured borosilicate glass for BIPV windows. Instead of depending on luminophores, this technique uses a single-step, scalable laser procedure to generate intricate nanostructures directly on the glass surface. These nanostructures are intended to effectively scatter incoming sunlight towards solar cells placed at the glass edges, working similarly to LSCs but without their disadvantages.  

Optimizing Results

The team used a femtosecond laser working at 520 nm to texture borosilicate glass wafers. By changing the laser scanning speed, they could manage the surface roughness and structure. Slower speeds produced rougher, less transparent surfaces with denser, fibrous nanostructures made through vapor condensation during laser ablation.  

Thorough analysis using methods like SEM, XRD, Raman, and photoluminescence spectroscopy aided in refining the procedure. While the laser treatment introduced minor structural imperfections and increased photoluminescence, the glass stayed mostly amorphous. Optical measurements indicated that laser treatment considerably altered reflection and transmission characteristics, with slower speeds generally raising scattering.  

Image by Aalto University, Materials & Design

Major Findings and Increased Efficiency

A proof-of-concept BIPV setup was constructed to test the nanostructured glass. The outcomes were significant:  

• Optimal Speed: Glass treated at a scan speed of 400 mm/s gave the best outcome.  
• Photocurrent Increase: This optimized glass produced a striking 55-times rise in photocurrent generation compared to untreated glass, showing much better light-guiding efficiency. This performance comes from a balance between the glass’s ability to scatter light well and permit light passage.  
• Estimated Efficiency: Although the prototype reached an optical efficiency of 0.66%, estimates based on light loss measurements point to a potential maximum efficiency near 10%, competitive with current LSC technology.  

Practical Benefits and Future Work

Besides efficiency, the study looked into practical points:

• Material Selection: Borosilicate glass was picked for its low thermal expansion property, preventing cracking during laser treatment, unlike soda-lime glass.  
• Scalability: While the lab work took time, modern industrial lasers could process large areas much quicker, making the technique potentially suitable for scaling up.  
• Transparency vs. Decoration: The lack of transparency can be managed by laser-patterning specific designs, offering aesthetic choices for architectural glass, though the effect on efficiency requires more study.  
• Self-Cleaning: Applying a thin fluoropolymer coating through plasma deposition turned the naturally very water-attracting laser-structured surface into a very water-repellent one. The optimal 400 mm/s sample obtained excellent water repellency (contact angles ~170°) with minimal sticking, allowing a self-cleaning “lotus effect”.  
• Durability: Although femtosecond-laser-treated glass is known for durability, additional tests are required to verify long-term function under real environmental conditions like UV exposure and moisture.