Multifunctional Additives with Cation−π Interactions Enable High-Performance Blue Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites, interspersed with organic intercalating cations, demonstrate significant potential in blue perovskite light-emitting quasi-2D perovskites, with organic intercalating cations, and show potential in blue perovskite light-emitting diodes (PeLEDs). However, the broad distribution of quantum wells, especially low-n phases, hinders energy transfer and device performance. Additionally, imperfect crystal quality and rough film surfaces further limit the efficiency. This study demonstrates that quaternary ammonium halides, like betaine hydrochloride (betaine HCl), can control phase distribution, passivate defects, and enhance crystallization in perovskite films. The cation−π interaction between betaine HCl and phenylethylammonium (PEA⁺) reduces low-n phases, while interactions with the C═O group and Pb²⁺ reduce defects and regulate crystallization. These improvements result in an enhanced radiative recombination. The devices achieve a maximum external quantum efficiency (EQE) of 17.09% at 478 nm and 22.66% at 485 nm, one of the highest reported for blue PeLEDs. This work provides new insights into the phase distribution in quasi-2D perovskites.