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The development of efficient metal-free organic emitters with thermally activated delayed fluorescence (TADF) properties for deep-blue emission is still challenging. A new family of deep-blue TADF emitters based on a donor-acceptor architecture has been developed. The electronic interaction between donor and acceptor plays a key role in the TADF mechanism. Deep-blue OLEDs fabricated with these TADF emitters achieved high external quantum efficiencies over 19.2 % with CIE coordinates of (0.148, 0.098).

Efficient organic emitters in the deep‐red region are rare due to the “energy gap law”. Herein, multiple boron (B)‐ and nitrogen (N)‐atoms embedded polycyclic heteroaromatics featuring hybridized π‐bonding/ non‐bonding molecular orbitals are constructed, providing a way to overcome the above luminescent boundary. The introduction of B‐phenyl‐B and N‐phenyl‐N structures enhances the electronic coupling of those para‐positioned atoms, forming restricted π‐bonds on the phenyl‐core for delocalized excited states and thus a narrow energy gap. The mutually ortho‐positioned B‐ and N‐atoms also induce a multi‐resonance effect on the peripheral skeleton for the non‐bonding orbitals, creating shallow potential energy surfaces to eliminate the high‐frequency vibrational quenching. The corresponding deep‐red emitters with peaks at 662 and 692 nm exhibit narrow full‐width at half‐maximums of 38 nm, high radiative decay rates of ca. 108 s−1, ≈100 % photo‐luminescence quantum yields and record‐high maximum external quantum efficiencies of ca. 28 % in a normal planar organic light‐emitting diode structure, simultaneously.

Metal halide perovskites are an emerging class of solution processable materials that have exhibited remarkable optoelectronic properties, such as high carrier mobility 1 , long diffusion length 2,3 , bandgap tunability 4,5 , high luminescence efficiency 6 and narrow emission bandwidth 7 . These properties, along with the ease of preparation of halide perovskite materials, have led to great advances in applications such as solar cells [8][9][10][11] , photodetectors 12,13 and light-emitting diodes (LEDs) [14][15][16][17] . The development of perovskite LEDs (PeLEDs) has, in particular, been rapid: in 2014 we reported electroluminescence (EL) from halide perovskites 14 and by 2018 we and others had achieved external quantum efficiencies of >20% 18-21 .