Mixed 2D/3D perovskite with fine phase control modulated by a novel cyclopentanamine hydrobromide for better stability in light-emitting diodes

The mixed 2D/3D perovskite has been proved to be a promising candidate to increase the exciton binding energy in perovskite light-emitting diodes (PeLEDs). However, the complex phase distribution and impurity (usually referring to ligands) limit the stability of the corresponding PeLEDs. Here, a novel molecule, cyclopentanamine hydrobromide (CyPA·HBr), is adopted to construct a mixed 2D/3D perovskite by partial substitution of FA with CyPA, realizing fine phase control for improved device stability. The adoption of CyPA·HBr helps to tune perovskite grain growth and passivate the defect, resulting in high coverage and smooth thin film with improved photoluminescence property. The PeLEDs with an optimized CyPA·HBr concentration of a molar ratio of 40% exhibit a pure green emission with a full width at half maximum of 22 nm, an external quantum efficiency of 6.55%, and a maximum brightness of 9408 cd m⁻² simultaneously. Interestingly, the CyPA·HBr-based device shows a half-lifetime two times longer than the one based on the most commonly used ligand of phenethylammonium bromide (PEA·HBr), assigned to the better phase control ability of CyPA·HBr in 2D/3D perovskite. Those results testify the importance of ligands to modulate perovskite phase along with efficient passivation defects for better stability of PeLEDs.