Magnetic Field Enhancement of Organic Light‐Emitting Diodes Based on Electron Donor–Acceptor Exciplex. (17th November 2015)

• Record Type: Journal Article
• Authors: Basel, Tek; Sun, Dali; Baniya, Sangita; McLaughlin, Ryan; Choi, Hyeonho; Kwon, Ohyun; Vardeny, Z. Valy
• Is Part Of: Advanced Electronic Materials. Volume 2:Number 2(2016)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2015-11-17
• Subjects: exciplexes -- magneto‐electroluminescence -- magneto‐photoluminescence -- organic light‐emitting diodes -- thermally activated delayed fluorescence; Materials -- Electric properties -- Periodicals; Materials science -- Periodicals; Magnetic materials -- Periodicals; Electronic apparatus and appliances -- Periodicals; 537
• DOI: 10.1002/aelm.201500248
• Languages: English
• ISSNs: 2199-160X

Abstract

Abstract : Reverse intersystem crossing (RISC) from triplet to singlet states has been recently introduced to photophysics of organic chromophores. One type of RISC occurs in donor (D)–acceptor (A) composites that form an exciplex manifold in which the energy difference, Δ E ST between the lowest singlet (S1 ) and triplet (T1 ) levels of the exciplex is small (<100 meV) thus allowing RISC at room temperature. This adds a delayed component to the photoluminescence emission that is widely known as thermally activated delayed fluorescence. Here, it is found that the electroluminescence in organic light‐emitting diodes (OLED) based on electron D–A exciplex is significantly enhanced (up to ≈40%) by applying magnetic field, due to the existence of an additional spin‐mixing channel between singlet and triplet states in the exciplex. The large magneto‐electroluminescence (MEL) in N, N, N ′, N ′‐tetrakis(4‐methoxyphenyl)benzidine: tris‐[3‐(3‐pyridyl)mesityl]borane [D–A] based OLEDs is demonstrated. These results are supported by magneto‐photoluminescence (MPL) measurements, and density functional theory calculations. Importantly, it is found that both MEL and MPL are thermally activated indicating the dominant role of the RISC process. The MEL( B ) response using the Δ g mechanism is analyzed, where the electron and hole g ‐values are different from each other because they reside in different molecules. Abstract : Pristine organic light‐emitting diodes based on donor–acceptor exciplexes show significant magneto‐electroluminescence (MEL) up to 40% at room temperature. The EL intensity, MEL, and magneto‐photoluminescence are all thermally activated, showing that the emission is determined by thermally activated delayed fluorescence. The large MEL is based on spin‐mixing related to thermally activated reverse intersystem crossing from the exciplex triplet to luminescent singlet.