1980 Eastman Kodak researcher Ching W. Tang solo-filed US4356429A 'Organic electroluminescent cell'—the precursor structure of OLEDs containing a porphyrin-based hole-injecting layer. Solely assigned to Kodak; Tang solo invention (DB correction: the popular 'Tang & Van Slyke co-invention' belief is incorrect; Van Slyke is a co-author of the 1987 Appl. Phys. Lett. 51:913 paper but absent from this patent's inventor field)

About excavation memos: "Excavation memos" in this series record candidate summaries at the stage where the primary URL has been confirmed. This memo retrieves the Claim 1, the inventor (Ching W. Tang solo), filing/grant dates, assignee (Eastman Kodak Co), and title from Google Patents, but the full specification (specific examples of porphyrinic compounds, the relationship to the 1987 Tang & Van Slyke two-layer paper, and Kodak internal OLED development documents) is unread. Only confirmed facts are stated; speculation is marked as such.

Why excavate this

OLED (organic EL) provides the material foundation for all modern (a) flagship Apple smartphone displays from iPhone X onward, (b) high-end Samsung Galaxy / Huawei Mate / Xiaomi Mix smartphones, (c) Samsung / LG / Sony premium TV displays, (d) foldable smartphones (Samsung Galaxy Z Fold/Flip, Huawei Mate X, Xiaomi Mix Fold, Vivo X Fold), (e) Apple Watch / Galaxy Watch small wearables, (f) Tesla Cybertruck / Mercedes EQS in-car HUDs, and (g) AR/VR headsets (Meta Quest 3, Apple Vision Pro, PICO 4 Micro-OLED) — i.e., arbitrary-shape light emission via organic thin films. The starting point was July 17, 1980, when Ching W. Tang at Eastman Kodak invented an organic electroluminescent cell containing a single-layer porphyrin-based hole-injecting layer; seven years later (1987), Tang and Van Slyke published the two-layer diamine HTL + Alq3 EML structure in Appl. Phys. Lett. 51:913. The subject of this memo, US4356429A, is the first patent of the seven-years-earlier single-layer porphyrin precursor structure.

The excavation establishes via primary sources that, as the title indicates ("Organic electroluminescent cell"), this patent is not the OLED two-layer-structure invention patent but the patent for the precursor single-layer porphyrin-based hole-injecting structure, and that the popular industry belief "Tang & Van Slyke co-invented OLED" does not match this patent's inventor field (Tang solo).

Patent basic information

• Patent number: US4356429A
• Title: Organic electroluminescent cell
• Inventor: Ching W. Tang solo
• Original Assignee: Eastman Kodak Co
• Current Assignee: Eastman Kodak Co (unchanged)
• Filing Date / Priority Date: 1980-07-17
• Grant Date: 1982-10-26
• Status: Expired - Lifetime (US patent term expired around July 17, 2002)

DB cross-check: Against the DB entry "Eastman Kodak Co, Ching W. Tang & Steven Van Slyke co-invention. 1980s patent," this yields one correction and one match confirmation.

• DB correction (inventor): DB "Tang & Van Slyke co-invention" is incorrect → actually Ching W. Tang solo. Van Slyke is a co-author of the 1987 Appl. Phys. Lett. 51:913 'Organic electroluminescent diodes' paper presenting the diamine HTL + Alq3 EML two-layer structure, but he is absent from this patent US4356429A's inventor field. This is the same "divergence between paper / textbook / award reporting and patent inventor names" pattern as Day 11 ICI beta-blockers (James Black absent), Day 12 sildenafil, and Day 9 PCR (Mullis solo award vs six co-inventors).
• DB match confirmation (Original Assignee and era): DB "Eastman Kodak Co, 1980s patent" matches the actual "Eastman Kodak Co, filed 1980-07-17 / granted 1982-10-26."

Day 8–18 has accumulated 23 corrections with 12 match confirmations.

Claim 1 (verbatim from primary source)

Claim 1 retrieved verbatim from Google Patents:

In an electroluminescent cell including an anode electrode, a cathode electrode, and a luminescent zone between said electrodes comprising an organic luminescent agent and a binder having a breakdown field strength of at least about 10⁵ volt/cm, the improvement comprising, between said luminescent zone and said anode electrode, a hole-injecting zone comprising a layer of a porphyrinic compound.

Three points in Claim 1's core:

1. "Improvement comprising"-style claim (Jepson-style): Claim 1 takes an existing electroluminescent cell (anode + cathode + luminescent zone) as a precondition and claims an improvement adding a porphyrinic-compound hole-injecting zone on the anode side. This indicates that this patent is not the invention of the organic EL cell itself but an invention of an improvement (adding the hole-injection layer) to the organic EL cell.
2. Single-layer porphyrinic compound: the hole-injecting zone is explicitly "a layer of a porphyrinic compound." This is a simpler single-layer structure than the 1987 Tang & Van Slyke two-layer (diamine HTL + Alq3 EML), still distant from the modern OLED 4–6-layer structure (HIL/HTL/EBL/EML/HBL/ETL/EIL).
3. Breakdown field strength of 10⁵ V/cm in the luminescent zone: the binder's electrical property is quantitatively specified. This presupposes field-driven operation of the organic EL, somewhat different from the modern current-driven OLED (electroluminescence vs current-injection emission).

Specification pitfall: this patent is not the "world's first OLED" invention patent. Organic electroluminescence itself was discovered by Bernanose in 1953; in 1965, Pope/Magante/Kallmann observed electron-injected electroluminescence in anthracene single crystals (J. Chem. Phys. 38:2042). Tang's contribution in this patent US4356429A is (i) the addition of the porphyrin-based hole-injecting layer and (ii) a path toward thin films and lower drive voltage, which became the precursor to the 1987 Tang & Van Slyke two-layer paper (Appl. Phys. Lett. 51:913). The 1987 paper is a separate document from this patent and presents the diamine HTL + Alq3 EML two-layer structure; the paper cites this patent US4356429A (via secondary industry sources; original unconfirmed).

Why Tang is solo and Van Slyke is absent (speculation)

Steven A. Van Slyke was Tang's colleague researcher at Eastman Kodak and is widely known as a co-author of the 1987 paper, but he is absent from this patent's inventor field. The following are speculative reasons (not confirmed at the primary source level):

1. The seven-year gap between the patent filing (1980) and the paper publication (1987) suggests Van Slyke may have joined OLED development after 1980: in 1980, Tang completed the porphyrin-based hole-injection layer invention solo; afterwards, Van Slyke joined the Kodak team and they jointly established the diamine HTL + Alq3 EML two-layer structure (1987).
2. This patent is the single-layer porphyrin-based precursor, possibly a separate invention from the two-layer structure: Claim 1 covers a single-layer porphyrin improvement, while the 1987 two-layer structure was likely filed as separate patents (other Kodak OLED patent numbers, not investigated here, may include the two-layer-structure filing).
3. Tang's patent strategy may favor establishing core ideas as solo inventor: at large corporate research institutions like Eastman Kodak, even when multiple researchers are involved, the convention is often to prioritize the core-idea proposer as the sole inventor at filing — and Tang ended up as solo inventor for this case.

This is the same "divergence between paper / award reporting and patent inventor names" pattern as Day 11 ICI beta-blockers (James Black received the 1988 Nobel Prize in Physiology or Medicine and is the central figure in textbooks but is absent from the ICI patent inventor field) and Day 9 PCR (Kary Mullis received the 1993 Nobel Prize in Chemistry solo but the Cetus patent US4683195A has six co-inventors).

Eastman Kodak's OLED commercialization failure and tech transfer to Korea / China

Kodak held OLED-related patents from the 1980s through the 2000s and tried to commercialize displays, but filed for Chapter 11 bankruptcy on January 19, 2012, selling many OLED-related patents in the process.

The 2009 Kodak → LG Display OLED patent sale was the inflection point at which Kodak's OLED patent portfolio (including this patent US4356429A) flowed through Korean LG Display into mass production. Since this patent was filed in 1980, the US patent term had already expired around July 17, 2002 — already expired by the 2009 sale — but derivative patents and mass-production know-how were inherited by LG Display. Samsung Display held and developed a separate-lineage OLED patent portfolio, and the two companies became the center of the global OLED market. Chinese BOE / TCL CSOT entered mass production in the late 2010s by hiring engineers from Samsung / LG and acquiring patent licenses, and as of 2024 are growing rapidly in the Mini-LED + OLED hybrid market.

Modern correspondence hypothesis (speculation)

Reading the grading: identical is zero rows. The single-layer porphyrin-based structure of this patent is precursor research for modern multi-layer OLEDs; rather than direct material inheritance, it is more accurately read as inheritance of problem awareness and design direction. Compared with Day 18 ep67 (silicon solar cell, two identical rows) and ep68 (blue LED, one identical row), this article is the OLED excavation memo with the most "metaphor / strained" rows.

Unconfirmed

• Full text of the specification (only the Google Patents Abstract and Claim 1 retrieved; specific examples and data of porphyrinic compounds unread)
• Full text of the 1987 Appl. Phys. Lett. 51:913 Tang & Van Slyke paper (only title and authors confirmed)
• Kodak internal OLED development documents (1980–2009)
• Full text of the 1965 Pope/Magante/Kallmann anthracene electroluminescence paper (J. Chem. Phys. 38:2042)
• Exact patent number list and price of the 2009 Kodak → LG Display OLED patent sale
• 2012 Eastman Kodak Chapter 11 filing documents
• 1999 SK Display Corp JV agreement
• Citation relationship between Samsung Display's OLED patents and this patent
• Relationship between Chinese BOE / TCL CSOT OLED mass-production patents and this patent
• Foldable-OLED-related patents (Samsung / Huawei / Xiaomi) and their derivation from this patent
• Patent number for the 1987 Tang & Van Slyke two-layer structure (not retrieved here; separate-episode candidate)

Next actions

1. Treat the 1987 Tang & Van Slyke two-layer-structure patent (number not retrieved) as a separate-episode subject
2. Comprehensively investigate the patent number list of the Kodak → LG Display OLED patent sale
3. Treat Samsung Display's OLED patents on the "Korean derivative" axis
4. Treat Chinese BOE / TCL CSOT OLED patents on the "Chinese follow-on mass production" axis
5. Treat foldable-OLED-related patents on the "implementation form evolution" axis
6. This memo, alongside Day 18's Note ep67 (silicon solar cell) and ep68 (blue LED), forms the "absorbing light / generating light / generating light in arbitrary form" semiconductor-optics 3-piece set, taking the organic EL (arbitrary-form light generation) side

Reference links

• US Patent US4356429A (Google Patents): https://patents.google.com/patent/US4356429A/en
• 1987 Tang & Van Slyke paper (Appl. Phys. Lett. 51:913, paywalled): https://doi.org/10.1063/1.98799
• Eastman Kodak official OLED history archive: https://www.kodak.com/

Sister articles in the series

• Episode 61 (HW #1): 1948 Bell Labs Bardeen-Brattain point-contact transistor US2524035
• Episode 64 (HW #2): 1979 Goodenough Li-ion US4302518A
• Episode 67 (HW #3, same Day 18 as this article): 1954 Bell Labs silicon solar cell US2780765A
• Episode 68 (HW Memo #4, same Day 18 as this article): 1992 Nichia Nakamura InGaN blue LED US5578839

Day 18 forms the semiconductor-optics 3-piece set: "absorbing light (HW-006 silicon solar cell) / generating light (HW-005 InGaN blue LED) / generating light in arbitrary form (HW-009 Kodak OLED, this article)".