A periphery cladding strategy to improve the performance of narrowband emitters, achieving deep-blue OLEDs with CIEy < 0.08 and external quantum efficiency approaching 20%

Abstract

Deep-blue thermally activated delayed fluorescence (TADF) emitters with National Television System Committee (NTSC) standard (0.14, 0.08) and narrowband emission have been one of the challenging issues for organic light-emitting diodes (OLEDs). In this work, a novel molecular design strategy, periphery cladding, was used to design and synthesize three deep-blue multi-resonance TADF emitters, N,N, 5,9-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1- de ]anthracen-7-amine ( PAB ), 2,12-di- tert -butyl-5,9-bis(4-( tert -butyl)phenyl)- N , N -diphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1- de ]anthracen-7-amine ( 2tPAB ) and 2,12-di- tert -butyl-N,N,5,9-tetrakis(4-( tert -butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1- de ]anthracen-7-amine ( 3tPAB ). By cladding large steric hindrance tert -butyl unit at periphery of multi-resonance emitter, the intermolecular interactions were suppressed, thus reducing aggregation-induced emission quenching and improving the PLQY of emitter. 3tPAB with full periphery cladding exhibited higher PLQY (74.7%). As a result, the device based on 3tPAB acquired the best performance by using 1,3-di(9 H -carbazol-9-yl)benzene (mCP) with low polarity as host. The maximum external quantum efficiency (EQE max ), CIE coordinates, and full-width at half-maximum (FWHM) of 3tPAB -based device were 19.3%, (0.141, 0.076), and 26 nm, respectively. To our knowledge, this is the first report about narrowband TADF OLEDs with single host that EQE max approaches 20% while CIE coordinates meet the NTSC blue-light standard. • Three deep-blue multi-resonance TADF emitters were designed and synthesized. • A useful strategy was demonstrated to improve the performance of multi-resonance TADF emitter. • EQE max and CIE coordinates of the device based on 3tPAB exhibited 19.3% and (0.141, 0.076), respectively.