NTU Scientists Unveil Near-Invisible Ultrathin Solar Cells to Transform Windows into Power Generators

Breakthrough in Perovskite Solar Cell Technology at NTU Singapore

In a groundbreaking advancement for renewable energy, researchers at Nanyang Technological University (NTU) in Singapore have developed ultrathin perovskite solar cells that are nearly invisible to the human eye. These innovative cells, with absorber layers as thin as 10 nanometres, promise to turn everyday windows, building facades, and even wearable devices into subtle power generators. This development addresses a key challenge in urban solar energy adoption: harnessing sunlight from vertical surfaces without compromising aesthetics or functionality.

Perovskite solar cells, named after their crystal structure resembling the mineral perovskite, are hybrid materials made from organic and inorganic compounds, typically involving lead halides. They have gained attention since their debut in 2009 for their potential to achieve high power conversion efficiencies at low production costs compared to traditional silicon panels. NTU's latest innovation pushes this technology further by making it ultrathin and semi-transparent, opening doors for widespread building-integrated photovoltaics (BIPV).

The research, published on May 14, 2026, in ACS Energy Letters, demonstrates fully vacuum-processed cells using a p-i-n architecture. This structure includes a hole transport layer, the intrinsic perovskite absorber, and an electron transport layer, all deposited via thermal evaporation—a method that heats source materials in a vacuum chamber to form precise, uniform films without toxic solvents.

How Thermal Evaporation Enables Ultrathin Precision

The fabrication process begins with preparing a substrate, such as indium tin oxide (ITO)-coated glass. A self-assembled monolayer of spiro-TTB serves as the hole transport layer, followed by co-evaporation of methylammonium iodide (MAI) and lead iodide (PbI2) to form the methylammonium lead iodide (MAPbI3) perovskite absorber. Thickness is controlled by evaporation rates, achieving layers from 10 nm to 60 nm. Subsequent layers include C60 for electron transport, BCP buffer, and silver contact.

This vacuum-based approach ensures high optoelectronic quality, with low trap densities that maintain open-circuit voltage and fill factor comparable to thicker cells (300-900 nm). Unlike solution-processing, which can introduce defects, thermal evaporation yields continuous, smooth films, as confirmed by field-emission scanning electron microscopy and atomic force microscopy.

Step-by-step, the process offers scalability for industrial roll-to-roll manufacturing, crucial for commercializing thin-film solar tech. For Singapore's humid, cloudy climate, these cells excel under diffuse light, absorbing specific near-infrared wavelengths while transmitting visible light.

Impressive Performance Metrics and Transparency

Opaque prototypes showcase power conversion efficiencies (PCE) of approximately 7% for 10 nm absorbers, 11% for 30 nm, and 12% for 60 nm—remarkable for such minimal material use. In semi-transparent configurations, a 60 nm cell achieves 7.6% PCE with 41% average visible transparency (AVT), yielding a light utilization efficiency (LUE) of 3.13%. A 30 nm variant promises even higher potential LUE of 5.15%.

LUE, calculated as PCE multiplied by AVT, balances energy generation and light passage, ideal for windows. Color neutrality (color rendering index ~79.7) ensures natural views, unlike tinted panels. Quantum confinement in ultrathin layers widens the bandgap, reducing visible absorption and enhancing transparency up to 65% AVT.

Compared to silicon BIPV (typically 10-15% PCE but opaque), these perovskites offer flexibility and lightness, weighing far less per watt generated.

• 10 nm: High transparency, suitable for wearables
• 30 nm: Optimal LUE balance
• 60 nm: Best PCE-transparency trade-off for windows

Revolutionizing Building-Integrated Photovoltaics in Singapore

Singapore, a land-scarce city-state, aims for 3 gigawatt-peak (GWp) solar capacity by 2030 under the Green Plan 2030, up from the original 2 GWp after early achievement. Traditional rooftop solar covers only ~3% of projected demand; BIPV unlocks vertical surfaces like the 40% glass-covered skyscrapers in Marina Bay and Raffles Place.

A mid-sized office tower could generate hundreds of megawatt-hours annually, powering ~100 four-room HDB flats. Assoc Prof Annalisa Bruno, Cluster Director at ERI@NTU, notes: “The built environment accounts for roughly 40% of global energy consumption, so technologies that seamlessly convert buildings’ surfaces into power-generating assets are gaining urgency.”

First author Dr. Luke White adds: “This opens up new possibilities for sustainable architecture, such as tinted windows that generate electricity.” Independent expert Prof. Sam Stranks from Cambridge praises the control for large-area applications.

Photo by Danist Soh on Unsplash

NTU's Leadership in Perovskite Research

NTU's Energy Research Institute @ NTU (ERI@N) leads in halide perovskites, focusing on low-cost, scalable manufacturing via solution-processing and vacuum evaporation. Assoc Prof Bruno, principal investigator, has pioneered thermally evaporated perovskites, achieving 25.1% PCE with high stability in prior works—retaining 93% after 1,000 hours.

Recent innovations include lead-free stabilizers and tandem silicon-perovskite cells. ERI@N's Renewables & Low-Carbon Solutions cluster drives commercialization, with patents filed via NTUitive. Collaborations with industry validate processes, positioning NTU as a hub for Singapore's solar ecosystem.

In higher education, such research attracts top talent, fostering PhD programs and jobs in materials science and engineering.

Overcoming Perovskite Challenges: Stability and Scalability

Perovskites degrade under moisture, heat, and UV, but vacuum processing minimizes defects. Ultrathin designs reduce material stress, enhancing durability. NTU's inert protective layers from prior studies boost longevity.

Scalability via evaporation suits large substrates, unlike spin-coating. Cost projections: perovskites could undercut silicon by 5x, vital for Singapore's import-dependent energy (95% fossil fuels).

• Benefits: Low-temperature processing (<150°C), no solvents, uniform large-area films
• Risks: Ion migration in thin layers—mitigated by precise control
• Comparisons: Outperforms organic photovoltaics in efficiency, rivals CIGS in flexibility

Real-World Applications Beyond Buildings

Vehicle integration: Car windows/sunroofs charge EV batteries while parked. Wearables: Smart glasses lenses power displays. Facades: High-rises harvest diffuse urban light.

In Singapore, vertical BIPV could add 1 GWp by 2030, per SERIS-NUS estimates. Case studies: NTU's campus added 13,000 panels (S$5.7M investment), generating 70% more solar power.

Stakeholder views: Architects praise aesthetics; policymakers align with net-zero 2050 goals.

Singapore's Solar Ambitions and Higher Education's Role

The Green Plan 2030 quadruples solar to 3 GWp, emphasizing floating, vertical, and urban PV. Universities like NTU drive R&D; ERI@N's tandem cells hit 30%+ efficiency targets.

Higher ed impacts: Trains researchers for green jobs—professor, postdoc, research assistant roles booming. NTU's interdisciplinary programs blend engineering, materials, physics.

Statistics: BIPV market to grow 20% CAGR globally; Singapore leads Asia in per-capita solar patents.

Photo by Moritz Kindler on Unsplash

Future Outlook: Commercialization and Global Impact

NTU teams negotiate with firms for pilots; patent protects novel structure. Challenges: Scale stability testing, lifecycle analysis.

Outlook: By 2030, ultrathin BIPV could cut urban emissions 10-20%. Actionable: Architects specify perovskite glass; policymakers fund R&D.

Bruno envisions: “Our cells can be tuned... reducing carbon footprint.” This positions Singapore—and NTU—as solar innovation leaders.