Efficient CsPbBr₃ Inorganic Perovskite Light-Emitting Diodes via Lewis Acid–Base Reaction with Organic Small Molecule mCP

CsPbBr3 all-inorganic perovskite light-emitting diodes (PeLEDs) have received increasing attention in recent years due to their unique luminescent property and superior thermal stability. However, the low solubility of bromide precursors and the fast crystallization of perovskites usually cause the formation of discontinuous CsPbBr3 films with rough grains and large pinholes. This would increase the defects and nonradiative recombination and severely degrade the device electroluminescence (EL) performance. To tackle this issue, herein, the 1,3-bis(9H-carbazol-9-yl)benzene (mCP) small molecule was elaborately selected as an effective additive to enhance the film-forming ability of CsPbBr3 emissive layers. With the addition of mCP, the submicrometer-sized CsPbBr3 grains were reduced to nanometer range, and the resulting perovskite films became uniform and continuous. It was found that the electron pairs of N2– in mCP would donate to metal Pb2+ in CsPbBr3. Thus, the so-called Lewis acid–base reaction occurred, which could retard the fast crystallization process and contribute to the connection of perovskite grains. As such, the film roughness was decreased from 8.28 to 1.62 nm, and the carrier lifetime was increased from 2.49 to 68.39 ns. The CsPbBr3:mCP device with an optimized mass ratio of 1:0.10 exhibited a maximum luminance (L) of 21008 cd/m2, a maximum current efficiency (CE) of 3.74 cd/A, and the corresponding maximum external quantum efficiency (EQE) of 1.21%, far surpassing the EL performance of the pristine CsPbBr3 PeLEDs.