A Brief History of OLEDs—Emitter Development and Industry Milestones

Abstract

Organic light‐emitting diodes (OLEDs) have come a long way ever since their first introduction in 1987 at Eastman Kodak. Today, OLEDs are especially valued in the display and lighting industry for their promising features. As one of the research fields that equally inspires and drives development in academia and industry, OLED device technology has continuously evolved over more than 30 years. OLED devices have come forward based on three generations of emitter materials relying on fluorescence (first generation), phosphorescence (second generation), and thermally activated delayed fluorescence (third generation). Furthermore, research in academia and industry toward the fourth generation of OLEDs is in progress. Excerpts from the history of green, orange‐red, and blue OLED emitter development on the side of academia and milestones achieved by key players in the industry are included in this report.

Efficient Red Electroluminescence From Phenanthro[9,10‐d]imidazole‐Naphtho[2,3‐c][1,2,5]thiadiazole Donor‐Acceptor Derivatives

“…Efficient blue, green and red emission are essential for full-color displays. [1][2][3][4][5][6][7] For organic light-emitting diodes (OLEDs), long lasting intense efforts have been devoted to develop efficient blue emitters. [8] In contrast, organic fluorescent red emitters receive less attention partially owing to the fact that redemitting phosphorescent Ir-or Pt complexes have already achieved high performance.…”

“…Efficient blue, green and red emission are essential for full‐color displays [1–7] . For organic light‐emitting diodes (OLEDs), long lasting intense efforts have been devoted to develop efficient blue emitters [8] .…”

Multichromophore Molecular Design for Efficient Thermally Activated Delayed Fluorescence Emitters with Near-Unity Photoluminescence Quantum Yields

“…Given their huge potential in displays and solid-state lighting technologies, there remains continued strong interest in improving the performance of organic light-emitting diodes (OLEDs). [1][2][3][4] The emitters utilized in OLEDs dictate the performance and efficiency of the electroluminescent (EL) device. Over the years, researchers have explored different classes of emitters in OLEDs.…”

“…[15][16][17] The highly tunable emission, high photoluminescence (PL) quantum yields (FPL), and ready availability of the compounds at frequently low expense have earned TADF-based OLEDs the title of the third generation of OLEDs. 4 Efficient TADF emitters rely on a small singlet-triplet energy splitting (DEST) to achieve high RISC rates. [18][19][20] The molecular design is based on a small exchange integral between frontier molecular orbitals that is frequently obtained by separating and/or electronically decoupling the donor and acceptor fragments of the TADF molecule.…”

Electron-withdrawing Group Modified Carbazolophane Donors for Deep Blue Thermally Activated Delayed Fluorescence OLEDs

“…The development of purely organic thermally activated delayed fluorescence (TADF) emitters is considered as one of the most promising approaches to utilize singlet and triplet excitons to access highly efficient organic light-emitting diodes (OLEDs). 1,2,3,4 The design principle of generating a structure with spatially separated donor and acceptor moieties to limit the exchange integral between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) thereby leading to a small singlet and triplet excited state energy difference, ΔEST, has been a reliable and fruitful strategy to construct TADF emitters. To obtain a small ΔEST, there are at present at least six design strategies, which are twisted donor-acceptor, 1 multi-resonance, 5 spiro-conjugation, 6 exciplex, 7 excited-state intramolecular proton transfer (ESIPT) 8 and through space-conjugation.…”