Efficient sky-blue perovskite light-emitting diodes by regulating the quantum well distribution of quasi-2D perovskites by suppressing lattice distortion

The quantum confinement effect is an effective strategy to broaden the bandgaps of quasi-2D perovskites for achieving efficient blue perovskite light-emitting diodes (PeLEDs). However, reducing the quantum well (QW) width in quasi-2D PEA₂Cs_n−1Pb_nBr_3n+1 perovskites always induces a disordered QW distribution, which is detrimental to its electroluminescent performance. We disclose that low-n quasi-2D perovskites tend to freely distort octahedra forming γ-phase perovskites due to the lattice mismatch brought by small-size Cs⁺ ions. The short-chain ligand ethylammonium (EA) is then used to suppress the distortion of [PbBr₆]⁴⁻ octahedra by partially entering the A-site interspace as a larger cation. The quasi-2D perovskites prepared with the mixed EA/PEA ligands exhibit a narrow diffraction peak with little octahedral distortion, uniform QW distribution and efficient energy transfer process. The sky-blue PeLEDs prepared with the proposed strategy of mixed EA/PEA ligands achieve a remarkable external quantum efficiency of 14.14%.