Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

Abstract

Daniel Volz, "Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays," J. Photon. Energy 6(2), 020901 (), doi: 10.1117/1.JPE.6.020901. Abstract. Thermally activated delayed fluorescence (TADF) is an emerging hot topic. Even though this photophysical mechanism itself has been described more than 50 years ago and optoelectronic devices with organic matter have been studied, improved, and even commercialized for decades now, the realization of the potential of TADF organic light-emitting diodes (OLEDs) happened only recently. TADF has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence. In this review, the TADF concept is introduced in terms that are also understandable for nonchemists. The basic concepts behind this mechanism as well as state-of-the-art examples are discussed. In addition, the future economic impact, especially for the lighting and display market, is addressed here. We conclude that TADF materials are especially helpful to realize efficient, durable deep blue and white displays.

Elucidating the Spatial Arrangement of Emitter Molecules in Organic Light‐Emitting Diode Films

“…[2] However,c urrently available experimental methods lack the resolution required to locate each Ir(ppy) 3 guest molecule within the film, and thus there is little direct experimental evidence that the guest molecules are isolated or evenly distributed. NR measurements,f or example,c annot distinguish between whether the Ir(ppy) 3 are isolated or form dimers or even larger clusters in the film. Thes patial distribution of the guest and host molecules in af ilm is important for understanding the behavior of phosphorescent emitters used in OLEDs,a s well as other materials such as thermally-activated delayed fluorescence emitters [3,4] and low donor content solar cells.…”

“…NR measurements,f or example,c annot distinguish between whether the Ir(ppy) 3 are isolated or form dimers or even larger clusters in the film. Thes patial distribution of the guest and host molecules in af ilm is important for understanding the behavior of phosphorescent emitters used in OLEDs,a s well as other materials such as thermally-activated delayed fluorescence emitters [3,4] and low donor content solar cells. [5] Films of phosphorescent light-emitting materials can undergo triplet-triplet annihilation (TTA), with the level dependent on the spatial distribution of the emitters.…”

“…[1] It is generally assumed that at the low concentrations [1-10 weight percent (wt %)] used, the emissive guests are evenly distributed throughout the host. Indeed, neutron reflectometry (NR) measurements show that the archetypical phosphorescent emissive layer, 6-12 wt %o ffac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy) 3 ]i n4 ,4'-bis(N-carbazolyl)biphenyl (CBP), has an even concentration of Ir(ppy) 3 throughout the depth of the film. [2] However,c urrently available experimental methods lack the resolution required to locate each Ir(ppy) 3 guest molecule within the film, and thus there is little direct experimental evidence that the guest molecules are isolated or evenly distributed.…”

“…[11] Ratcliff et al [12] have mimicked the process of deposition of an 8wt% Ir-(ppy) 3 :CBP blend using aM onte Carlo procedure in which individual molecules with af ixed geometry were added sequentially in af ixed order to ag rowing layer. The coordinates of each molecule added were then frozen, which ensured the emitter molecules were uniformly distributed within the matrix.…”

Recent progress of pyrimidine derivatives for high-performance organic light-emitting devices

“…[11][12][13] Recently, thermally activated delayed fluorescence (TADF) emitters based on pure organic compounds have been considered as an alternate technology to phosphorescent counterparts to realize an IQE of 100%. [14][15][16][17][18][19][20][21][22][23][24][25] Until recently, several TADF OLEDs have achieved a high EQE of over 30% at maximum. [26][27][28][29][30][31][32] The efficiency of the TADF-based OLEDs is expected to exceed that of OLEDs based on phosphorescent emitters due to the unlimited molecular design of pyrimidine derivative-based TADF emitters.…”