TOPCon Solar Cells Show Near‑Zero Degradation

TOPCon cells degrade barely at all – the bottom line

Researchers at the U.S. Department of Energy’s National Laboratory of the Rockies have shown that light‑ and elevated‑temperature‑induced degradation (LeTID) in industrial n‑type TOPCon silicon solar cells is practically negligible. Even under accelerated LeTID stress, the efficiency loss stayed within typical warranty tolerances, especially when the cells were fired with a slow‑cooling profile or treated with laser‑enhanced contact optimization (LECO).

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Why LeTID was a pain point for older PERC panels

The previous generation of silicon PV was dominated by p‑type PERC cells built on boron‑doped Czochralski (Cz) wafers. Those wafers suffered from two bulk‑defect phenomena: light‑induced degradation (LID) and LeTID. Switching the dopant to gallium eliminated LID, but LeTID persisted, causing noticeable efficiency drops over time in hot climates. This reliability issue has been a major driver for manufacturers to move toward n‑type technologies such as TOPCon, which theoretically avoid both bulk defects.

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How the US lab proved TOPCon’s resilience

The team tested n‑type Cz wafers doped with phosphorus (P), antimony (Sb) and arsenic (As). All wafers received a symmetric SiNₓ:H passivation, were fired at 800 °C, then subjected to a recovery step (20 °C, 2‑sun illumination) before being exposed to LeTID stress (120‑130 °C, 1‑sun illumination). Key findings:

• Defect density: As‑doped wafers showed a higher defect density than P‑ and Sb‑doped wafers, but the absolute values remained well below those reported for p‑type Ga‑doped PERC.
• Degradation magnitude: Across all dopants, the net efficiency loss after extended LeTID stress was small for cells fired with a low cooling rate, and notably less than that observed for legacy PERC cells.
• LECO advantage: Cells that received laser‑enhanced contact optimization exhibited a modest further reduction in open‑circuit‑voltage loss, helping keep total degradation comfortably inside standard warranty limits.
• Recovery benefit: After the LeTID stress, a regeneration step actually increased bulk carrier lifetimes beyond the initial recovery level, indicating that the process can improve material quality.

These results were published in Solar Energy Materials and Solar Cells and corroborated by independent industry analyses that note TOPCon’s superior long‑term stability,.

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What the numbers mean for solar‑module warranties

Most manufacturers guarantee limited power‑output loss over the warranty period. The lab’s TOPCon cells remained well within those limits, whereas legacy p‑type PERC modules can exhibit higher losses in hot, sunny regions, potentially affecting the economic case for long‑term installations.

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What it means for Israel

Israel’s residential solar market typically installs about 10 kWp rooftop systems in the central region, yielding roughly 17 000 kWh / year at the average residential tariff of ₪0.48 /kWh. With an installation cost of about ₪31 500 (≈₪3 150 per kWp), the simple payback is roughly four years over the system’s lifetime. For commercial rooftops, the cumulative savings scale proportionally, reinforcing the business case for adopting TOPCon‑based modules now that their long‑term reliability is demonstrated.

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Outlook: TOPCon set to become the new standard

With LeTID largely mitigated, manufacturers can focus on other performance levers—higher cell efficiencies, bifacial designs, and cheaper wafer production. As the Israeli government pushes toward its 30 % renewable‑electricity target by 2030, the durability advantage of TOPCon will help meet the 20 % target for 2025 without inflating OPEX. Installers and investors should start specifying TOPCon modules, especially for large‑scale rooftop and ground‑mount projects where every percentage point of output matters.

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Sources

• Interview with principal investigator Paul Stradins, pv‑magazine (original source).
• Independent analysis of TOPCon stability, PV‑Tech.
• Peer‑reviewed paper in Solar Energy Materials and Solar Cells.