Ethylenediammonium-asisted phase control and in-situ passivation of all-bromine quasi-2D perovskite for efficient pure-blue light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskites with pure bromine components have emerged as promising candidates for blue light-emitting diodes (LEDs). However, the broad-width distribution of quantum wells generally results in sky-blue emission due to the cascade energy transfer. The presence of low-n phases (n defined as the number of inorganic monolayers) are also feasible to induce electron–phonon coupling and subsequent non-radiative recombination loss. Thus, the elaborate control over the phase distribution of quantum wells and effective in-situ passivation have been essential factors to achieve high-performance pure-blue quasi-2D perovskite LEDs (PeLEDs). In this work, we report a novel organic spacer ligand ethylenediammonium trifluoroacetate (EDATFAc 2 ) to simultaneously modulate the emission wavelength and passivate defects of quasi-2D perovskite. The large spacer EDATFAc 2 can interact with PbBr 6 4- octahedra and PEA + cations to slow down the crystallization kinetics and facilitate homogenous distribution of precursor components, finally eliminating both small-n domains and large-n domains. Such concentrated phase distribution and robust defect passivation contribute to high-performance blue quasi-2D perovskite emitter. This work clearly shows that the functional spacer ligand can provide powerful strategy to achieve blue quasi-2D PeLEDs with pure bromine components.