Technical notes

OLED material COAs: what 3N, 4N and 5N purity really tell you

Laurand Chem · 9 November 2026 · 7 min read

A certificate of analysis for an OLED intermediate usually carries two purity claims: an HPLC area percent and a grade written in Ns — 3N, 4N, sometimes 5N. Buyers routinely read them as the same measurement. They are not, and the gap between them explains most of the surprises we hear about: a “5N” material that decomposes on the evaporation boat, or a device that darkens after a few hundred hours on material that looked clean on paper.

Two purity numbers that are not the same measurement

The N notation comes from inorganic chemistry, where “4N” means 99.99% total purity and is backed by a traceable analysis of everything that is not your substance. In the organic intermediate trade the same notation is often used as shorthand — sometimes supported by data, sometimes not. Unless the certificate states which method produced it, an N grade tells you about the supplier’s marketing, not the material.

HPLC area percent measures something narrower: organic impurities only, at the chosen detection wavelength, relative to the main peak. A material can read 99.6% by HPLC and still carry 50 ppm of sodium or 0.4% water — neither of which appears in that number. For a device driven by thin films a few dozen nanometres thick, the metals and the water are often the parts that matter most, and they are precisely the parts neither number covers.

What sublimation removes — and what it leaves

Vacuum sublimation is the standard final purification step for OLED transport, host and dopant materials. It is genuinely effective at what it is designed to do: removing non-volatile residues — inorganic salts, catalyst residues, high-boiling tars — and improving the particulate cleanliness of the material. What it does not do is separate structural isomers or close-boiling organic impurities; those co-sublime with the product.

So “sublimed, 5N” is a processing statement, not a purity guarantee. The correct reading is: the material has been through a sublimation step, the non-volatile fraction is low, and the HPLC purity is whatever the chromatogram says. When a supplier quotes a sublimed grade, ask for the chromatogram of the sublimed batch — not the crude material it came from.

What a real electronic-grade COA carries

Test	Method	What to require	What it protects
Organic purity	HPLC (UV) or GC-FID, area%	Chromatogram, wavelength and gradient stated	Device efficiency, lifetime drift
Largest single impurity	Same chromatogram	Identify and limit the largest unspecified peak	Batch-to-batch reproducibility
Metallic impurities	ICP-MS	Elements named (Na, K, Li, Fe, Ni, Cr, Cu), ppm limits, batch-specific	Charge trapping, dark spots, pixel defects
Water	Karl Fischer	Not “loss on drying” for hygroscopic amines and carbazole derivatives	Film quality, hydrolysis on storage
Residual solvents	GC headspace	Declared against ICH Q3C classes	Outgassing, bubble formation in evaporation
Thermal behaviour	TGA / DSC	Onset of decomposition; weight loss at deposition temperature	Decomposition on the evaporation boat

Three of these lines — metals, water and thermal behaviour — are the ones most frequently missing from certificates offered at the “electronic grade” price. They are also the three a device maker notices first.

Why two 4N lots behave differently

Two lots can carry identical HPLC purity and still evaporate differently. The usual suspects, in order of how often we see them:

Thermal stability. A compound that starts to decompose at 30 degrees below its sublimation point will partly crack on the crucible no matter how pure the chromatogram is. TGA is the only line on the certificate that predicts this.
Water content. Hygroscopic amine intermediates pick up moisture in transit; the water leaves as a burst of vapour early in the deposition and disturbs the film.
Metal traces. Sub-visible on HPLC, decisive on a device. A producer without routine ICP-MS cannot control this, whatever the grade label says.

This is why device makers qualify suppliers by an evaporation trial rather than by grade, and why a COA without TGA and ICP-MS data is an incomplete document for anything that goes into a vacuum chamber.

The specification we would ask for

Seven lines, and the quotes come back comparable:

1. Organic purity: HPLC/GC area% with chromatogram, method and wavelength named
2. Largest single unspecified impurity, with a written limit
3. Metallic impurities: ICP-MS, elements and ppm limits, batch-specific
4. Water: Karl Fischer
5. Residual solvents: GC, declared against ICH Q3C
6. Thermal: TGA onset of decomposition and weight loss at deposition temperature
7. Packaging: inert gas, amber glass, headspace volume, retest period

Line 6 is the one buyers leave out most often, and the one that most directly predicts how the material performs in the vacuum chamber. If you sublime in-house from crude material, line 6 applies to your crude spec instead — together with non-volatile content, which becomes your own yield calculation.

Sourcing notes from China

OLED intermediates sit at very different points on the processing curve, and the price reflects processing far more than synthesis:

Crude material is what most producers make and stock. It is chemically the same compound; the difference is everything the certificate does not yet prove. Buying crude and subliming in-house is a legitimate strategy if you have the equipment and the yield loss is priced into your process.
Sublimation capacity is the bottleneck. Vacuum sublimation lines are capital-intensive and slower than synthesis, which is why sublimed lots carry longer lead times and a wider price spread between producers than crude.
Batch variance concentrates in metals and water, not in HPLC purity. A producer who runs ICP-MS on every batch can prove consistency; one who runs it on qualification batches only is asking you to trust an average.
Packaging matters more for these materials than for ordinary fine chemicals: inert gas blanket, amber glass for photolabile carbazoles, minimal headspace, and a retest period stated on the label.

One structural point: “electronic grade” has no universal definition. It is whatever the attached specification defines, so the specification — all seven lines — is the product. We would rather send a complete specification than a bigger grade label.

How we can help

Laurand Chem supplies OLED intermediates — boronic acids, carbazoles, arylamines and host building blocks — from qualified Chinese producers, with batch-specific COAs including chromatograms, ICP-MS data and TGA traces where the application requires them. Send us the seven lines above and we will return a specification sheet and a quote, or tell you plainly which of the seven the grade you need cannot currently support.

Request a quote or specification sheet