LID

What is LID

LID, Light-Induced Degradation, is the initial loss of efficiency in crystalline silicon solar cells during the first 100 hours of exposure to sunlight. It is caused primarily by the formation of boron-oxygen complexes in p-type silicon containing both boron dopant and oxygen impurities. The defect traps electrons, reducing open-circuit voltage and short-circuit current, lowering Pmax by 1 to 2.5 percent.

LID was first identified in the 1970s and became a major concern for p-type PERC in the 2010s as module-level efficiencies pushed higher. The mechanism is intrinsic to boron-doped p-type silicon. Switching to gallium doping or to n-type silicon (TOPCon, HJT) eliminates most or all of the mechanism.

For Indian solar, LID is built into all modern warranty curves and yield models. A new module is expected to drop 1 to 2 percent in its first month and then degrade linearly thereafter.

LID explained simply

When you first turn on a solar panel and leave it in the sun, the output drops by about 1.5 percent in the first month and stabilises. After that, the year-on-year degradation is a slower 0.5 percent or so.

The reason: tiny defects form when light hits silicon containing certain impurities. The defects make a small fraction of the silicon less efficient at converting sunlight. Once all the possible defects have formed, the loss stops.

Why LID matters

Warranty curves. Manufacturer linear performance warranty includes LID as the first-year drop.

Yield modelling. P50 yield models apply LID derate in year 1, one of several loss factors covered in Solar Yield in India, kWh-per-kW Benchmarks by State.

Technology comparison. PERC has LID; TOPCon has less; HJT has effectively none.

Cell technology selection. LID is one factor pushing the industry toward n-type cells.

Financial bankability. Lenders model LID conservatively.

How LID works

Mechanism in p-type PERC:

1. Silicon contains boron (dopant) and small amounts of oxygen (impurity from Czochralski growth).
2. Sunlight excites electrons in the silicon.
3. Excited electrons combine with boron-oxygen pairs to form a recombination-active defect.
4. The defect traps subsequent electrons, reducing minority carrier lifetime.
5. Reduced lifetime lowers Voc and Isc, hence Pmax.
6. After 100 hours, all available B-O pairs have formed defects. Degradation stops.

The defect is reversible by thermal annealing in the dark, but in field conditions modules stay illuminated, so reversal is not practical.

Technical deep dive

Magnitude by cell technology

Boron-oxygen defect

The B-O complex involves substitutional boron, interstitial oxygen, and an additional silicon site. Light excitation drives the complex into a metastable state with high recombination activity.

IEC 61215 light-soaking test

The standard module qualification test includes a light-soaking step to stabilise modules before final efficiency measurement. Typical exposure: 5 to 60 hours at 1000 W/m².

Stabilised vs nameplate output

Some manufacturers quote nameplate Pmax including LID effect; others quote pre-LID. Customers should specify “stabilised Pmax” in purchase orders.

Real-world applications

First-year yield modelling for solar plants, often run through tools like SurgePV’s solar simulation software to capture LID derate alongside other loss factors.

Performance warranty enforcement.

Module technology selection.

PPA negotiation around year-one generation.

Indian PR (Performance Ratio) measurement during commissioning year.

Advantages of low-LID modules

Higher first-year yield.

Closer match between nameplate and field output.

Simpler warranty enforcement.

Better PR in commissioning year.

Limitations

LID is intrinsic to p-type silicon. Cannot be eliminated for PERC without doping changes.

Annual degradation continues after LID. Total lifecycle loss is sum of LID + annual.

n-type alternatives (TOPCon, HJT) cost more.

Common problems

Customer perception of underperformance in first year, often attributable to LID.

Yield model not including LID, leading to apparent first-year shortfall.

Performance warranty dispute over what “100 percent” baseline means.

Confusion between LID and soiling (LID is permanent, soiling is recoverable).

Best practices

Specify “stabilised Pmax” in purchase orders.

Apply LID derate in first-year yield models.

Educate customers on expected first-year performance.

Reference IEC 61215 light-soak test in module specifications.

Choose gallium-doped PERC or n-type TOPCon for low-LID applications.

Comparison: LID across silicon types

Indian market context

Indian ALMM-listed modules typically include LID in their performance warranty curves.

Major Indian manufacturers have transitioned to gallium-doped PERC and increasingly to n-type TOPCon, reducing field LID, as with the ALMM-listed mono PERC modules deployed in Punjab Dairy Farm Solar, Replacing Diesel with Clean Energy.

Yield models used in SECI and CPSU tender bids include LID derate in year 1.

Commissioning-year PR measurements should account for LID.

PM Surya Ghar performance expectations are typically computed on stabilised output, not nameplate.

Standards and certifications

Common mistakes

Quoting nameplate Pmax without specifying LID status.

First-year yield model omits LID, causing apparent underperformance.

Customer dispute over first-year output without LID baseline.

Mixing LID-affected and LID-free modules in yield averages.

Confusing LID with LeTID.

Key takeaways

LID is the initial efficiency loss in the first 100 hours of solar exposure for p-type silicon modules. Mainstream PERC loses 1 to 2.5 percent; gallium-doped PERC less; TOPCon and HJT effectively eliminate LID. Modern warranty curves and yield models include LID. The Indian industry is migrating toward n-type cell technologies that minimise LID and provide higher stabilised efficiency.

Further reading

For how LID plays out in real projects, these guides go deeper:

• How to Evaluate Solar Inverter Reliability
• Solar Inverter Commissioning in India: Setup Guide
• Anti-Islanding Protection in Solar Inverters
• Aurora Solar Review 2026: Pricing, Strengths and Where It Falls Short

Sources

• Schmidt J., Aberle A. G., Hezel R., Investigation of carrier lifetime instabilities in Cz-grown silicon, Proceedings of IEEE PVSC, 1997.
• IEC 61215, Module qualification and type approval.
• IEC TS 63209, Extended-stress testing of PV modules.
• IEC TS 61853-4, Performance testing under operating conditions.
• IS 14286, Indian Standard for crystalline silicon PV modules.
• ITRPV Roadmap, latest edition, VDMA.
• NREL Technical Report TP-5J00-78211, PV Module Degradation Rates.
• Glunz S. W., et al., Light-induced degradation in crystalline silicon solar cells, Progress in Photovoltaics, various.
• IEA PVPS Task 13 Report on PV performance and reliability.