🔬 Unveiling the Self-Repair Process in High-Efficiency Silicon Solar Cells

Silicon solar cells, the backbone of modern photovoltaic (PV) technology, face a persistent challenge from ultraviolet (UV) radiation in sunlight. This UV-induced degradation (UVID) can weaken the performance of even the most advanced cells, such as Tunnel Oxide Passivated Contact (TOPCon) designs, by disrupting chemical bonds at the surface. Researchers at the University of New South Wales (UNSW) Sydney have now cracked the code on this issue, developing a groundbreaking real-time monitoring technique that captures the self-repair mechanism in action. Their work, published in Energy & Environmental Science, reveals how ordinary visible light triggers atomic-level recovery, restoring efficiency losses of up to 10% observed after accelerated UV exposure equivalent to 2,000 hours.

This discovery is particularly timely for Australia, where rooftop solar installations exceed 43 gigawatts (GW) as of late 2025, making the nation a global leader in PV adoption. With high UV exposure due to the country's sunny climate, innovations like this could extend panel lifespans and boost reliability, supporting the push toward net-zero emissions.

How UV Radiation Damages Solar Cells: A Step-by-Step Breakdown

UVID occurs primarily near the surface passivation layer of silicon solar cells. Passivation layers, often made of silicon oxide or nitride, protect the silicon wafer and minimize recombination losses where charge carriers are wasted as heat. When UV photons hit, they provide enough energy to break silicon-hydrogen (Si-H) bonds and rearrange interactions with boron atoms, creating defects that increase surface recombination.

The process unfolds in stages:

• Initial Excitation: UV light (wavelengths below 400 nm) penetrates the anti-reflective coating and excites electrons in the passivation layer.
• Bond Breaking: Si-H bonds fracture, releasing hydrogen atoms deeper into the material and exposing boron-oxygen complexes.
• Defect Formation: These changes raise the surface recombination velocity, dropping power conversion efficiency (PCE) by 3-11% in lab tests.
• Performance Dip: Current-voltage (I-V) curves show reduced fill factor and open-circuit voltage.

Previous studies noted this degradation but couldn't observe it dynamically without destroying the cell. UNSW's approach changes that completely.

The Revolutionary Ultraviolet Raman Spectroscopy Technique

At the heart of the breakthrough is ultraviolet Raman spectroscopy, a laser-based method that probes molecular vibrations non-destructively. Here's how it works step by step:

1. A UV laser (typically 325 nm) is directed at the operating solar cell.
2. Scattered light shifts in wavelength due to atomic vibrations, creating a spectrum unique to chemical bonds like Si-H or Si-B.
3. Spectra are recorded in real-time as the cell undergoes UV stress followed by visible light soaking.
4. Changes in peak intensities directly correlate with bond reconfiguration and repair.

This 'material camera,' as Dr. Ziheng Liu describes it, operates on intact TOPCon cells under realistic bias and illumination, unlike destructive techniques like secondary ion mass spectrometry (SIMS). The setup detected UV sensitivity in seconds, far faster than traditional days-long tests.

For those interested in hands-on research, UNSW's research jobs in photovoltaics offer opportunities to work with such cutting-edge tools.

Sunlight-Activated Self-Repair: Atomic-Level Insights

Once UV damage sets in, recovery kicks off under visible light (400-700 nm). Hydrogen atoms, freed by UV, migrate back to the surface passivation layer. They re-form Si-H bonds, passivate defects, and restore the original chemical structure. This material-level healing—confirmed for the first time—explains why cells rebound to near-original efficiency after light soaking.

Key findings from the study:

• Reversible degradation tied to passivation layer thickness; thicker layers slow H migration.
• No permanent boron-oxygen defects involved, unlike light-induced degradation (LID).
• Recovery time: minutes to hours under standard irradiance (1000 W/m²).

This mechanism favors designs balancing high initial PCE with robust self-healing over ultra-UV-resistant but costlier alternatives.Read the full paper.

Photo by Markus Winkler on Unsplash

Meet the Minds Behind the Discovery: UNSW's PV Powerhouse

Scientia Professor Xiaojing Hao, a leader in thin-film and silicon PV, spearheaded the project. Her team includes Dr. Ziheng Liu (corresponding author), Dr. Pengfei Zhang, and Dr. Caixia Li, all from UNSW's School of Photovoltaic and Renewable Energy Engineering. Supported by the ARC Research Hub for Photovoltaic Solar Panel Recycling and Sustainability (PVRS), this work builds on UNSW's 50-year legacy.

UNSW, home to 'father of photovoltaics' Professor Martin Green, holds historical records like the first 20% efficient silicon cell (1985) and 25% (2008). Today, their labs push TOPCon toward 27% PCE. Aspiring researchers can explore faculty positions or postdoc roles at such institutions via AcademicJobs.com.

"This new method can be used directly on the production line," Prof. Hao noted, highlighting its industrial potential.

Transforming Solar Manufacturing and Quality Control

The technique promises to revolutionize accelerated aging tests, which often overestimate degradation by inducing irreversible damage absent in field conditions. Manufacturers can now screen cells in seconds for UV vulnerability, optimizing passivation recipes and coatings.

In Australia, with rooftop PV at 26+ GW in the NEM grid, this could slash warranty costs and enhance exports. Check Australian university jobs for PV engineering opportunities.

🌞 Australia's Solar Boom and the Role of University Research

Australia's PV capacity hit 43 GW by 2025, driven by 4+ million installations. Yet high UV flux accelerates UVID, with studies showing 5-11% losses in TOPCon modules. UNSW's insights enable tailored designs for harsh climates, aligning with national goals like 82% renewables by 2030.

Stakeholder views: Industry welcomes faster QC; academics praise mechanistic clarity. For career advice, see how to craft an academic CV.

Future Outlook: Scaling Self-Repair Innovations

Next steps include automating Raman for production lines and testing on tandem cells. PVRS funding will integrate this with recycling, closing the sustainability loop. Globally, as TOPCon dominates (lab PCE ~27%), self-repair could add years to 25-30 year warranties.

• Potential: 1-2% lifetime yield gains.
• Challenges: Scaling UV lasers cost-effectively.
• Solutions: Hybrid AI-spectroscopy analysis.

Students eyeing PV careers should explore postdoc success tips.

Photo by Markus Winkler on Unsplash

Expert Perspectives and Real-World Case Studies

Dr. Liu: "The material itself is repairing at the atomic level." This echoes field data where Australian panels recover post-winter UV dips. Case: A 2025 RETC study found 40% TOPCon modules >5% UVID, recoverable via light soak.

Compared to perovskite self-healing (ion migration), silicon's H-based repair is more robust for mass production. UNSW full announcement. PV Magazine coverage.

Career Pathways in Photovoltaic Research at Australian Universities

This UNSW publication underscores demand for PV experts. Roles span research assistants to professors, with salaries averaging AUD 115k for lecturers.Learn to become a lecturer. Platforms like higher-ed jobs, university jobs, and research jobs list openings at UNSW and beyond. Rate professors via Rate My Professor.

Browse Australian academic opportunities or career advice for actionable insights.