Korean Supreme Court upholds LG Chem patent for longer-lasting OLEDs

In a six-year patent invalidation dispute between LG Chem and SFC Co., Ltd., the South Korean Supreme Court has upheld LG Chem’s patent relating to technology for extending the lifetime of organic light-emitting diodes (OLEDs). The ruling is notable not only for its significance to a key OLED material but also for its assessment of demonstrated technical effects and post-filing evidence submitted in support of such effects.

Decision 2024Hu11125, rendered on May 14 2026, also puts LG Chem in the driving seat of a separate, ongoing infringement action against SFC, a domestic joint venture between Samsung Display and Japan’s Hodogaya Chemical Co., Ltd.

In 2019, LG Chem acquired several OLED technologies, including the patent at issue, from US chemical company DuPont. The patent is directed to a deuterated anthracene-based compound useful as a blue OLED host material. Through deuteration, the compound enables a significant improvement in the lifetime of blue OLED without sacrificing other properties.

SFC and Japanese company Idemitsu Kosan, which had been monitoring the technology, promptly initiated invalidation actions before the Intellectual Property Trial and Appeal Board (IPTAB) in the same year, triggering the dispute.

Before the IPTAB, the petitioners argued that the patented invention was substantially identical to inventions disclosed in earlier-filed but later-published patent applications and therefore lacked novelty under the enlarged concept of novelty. They also argued that the invention lacked an inventive step over a combination of prior art references and that the specification failed to satisfy the support and enablement requirements.

In response, LG Chem corrected the claims to limit the claimed compound to one with at least 40% deuteration and strongly refuted the petitioners’ arguments. After three years of proceedings, the IPTAB finally ruled in favour of LG Chem in June 2022. Both petitioners appealed to the Intellectual Property High Court (the IP High Court).

In 2023, LG Chem filed a correction trial seeking to further define the at-least 40% deuterated compound in the claims. In particular, the claims were corrected to require that the compound (of the formula below) be at least 40% deuterated, that substituents R¹ to R⁸ be deuterium, that at least one of Ar¹ to Ar⁴ be deuterated, and that at least one of Ar¹ to Ar⁴ comprise at least one hydrogen.

The IPTAB accepted the correction in October 2023, and the IP High Court accordingly heard the case based on the corrected claims. In September 2024, the IP High Court dismissed the appeals.

When considering the enlarged concept of novelty, the IP High Court found that:

• The earlier-filed but later-published patent applications did not disclose any anthracene-based compound as required by the corrected claims; and

• The patented compounds exhibited a significant improvement in OLED lifetime (measured by Raw T50, the time in hours for a device to reach half its initial luminescence) – showing an average increase of more than double compared with the comparative examples – without showing degradation in other properties such as luminous efficiency, brightness, and operating voltage.

The court considered this improvement – achieved through a high level of deuteration – to constitute a new technical effect.

Accordingly, the court concluded that the patented invention was novel over the earlier-filed but later-published patent applications, as the differences in technical features could not be regarded as mere additions, deletions, or modifications of well-known conventional technologies in the specific means for solving the problem.

With regard to inventive step, the court determined that neither of the prior art references disclosed or suggested the deuteration features required by the corrected claims, let alone the improvement in OLED lifetime through deuteration. The court further found that none of the prior art references disclosed or implied the technical concept of deuterating anthracene compounds for the purpose of improving the lifetime of blue OLEDs. It therefore concluded that the patented invention could not have been easily derived from the combination of the prior art references.

Finally, the court ruled that the specification sufficiently disclosed how to synthesise and identify the claimed compounds, measure their deuteration level, and manufacture OLEDs comprising such compounds. Accordingly, a person skilled in the art could readily prepare the claimed compounds as well as predict and confirm the lifetime-improving effect based on the disclosure and common general knowledge in the art. Furthermore, the court recognised post-filing data submitted by LG Chem in support of the technical effect.

Both petitioners appealed to the Supreme Court, but Idemitsu Kosan subsequently withdrew its appeal.

The Supreme Court upheld the lower court’s decision, reaffirming the established legal principles governing the enlarged concept of novelty, inventive step, and support and enablement requirements. It found no error in the lower court’s application of those principles or its assessment of the relevant facts of the case.

This case highlights the importance of establishing a clear technical effect when defending the validity of patents in Korea. It also illustrates how carefully calibrated claim amendments can strengthen that position mid-litigation. By narrowing the claims to specific deuteration and structural features, LG Chem was able to distinguish the claimed invention from the prior art while tying those differences to a demonstrated significant improvement and a new technical effect.

The court’s consideration of post-filing data in support of the technical effect further suggests that, where properly anchored in the original disclosure, such evidence can have meaningful evidentiary value in a validity dispute.

With the question of validity now out of the way, the focus shifts to the scope of protection of the patent at hand. Following its successful defence of the patent’s validity before the IP High Court, LG Chem filed an infringement lawsuit against SFC in December 2024. The action seeks significant damages as well as injunctions against the production, sale, and importation of the allegedly infringing products, together with disposal of inventory. The infringement action is pending before the Seoul Central District Court.

Given the significant influence that a patent validity decision can have on the outcome of infringement litigation in Korea, the Supreme Court’s final ruling puts LG Chem in a favourable position in the pending infringement action. While it remains to be seen whether SFC’s products ultimately infringe the patent, the outcome of the litigation could have broader implications for the competitive landscape and patent strategies in the OLED industry, particularly given SFC’s role as a supplier of key OLED materials to LG Chem’s domestic competitor, Samsung Display.