Multi-functional ion-pairing additive for efficient quasi-2D perovskite light-emitting diodes and solar cells.

[Display omitted] • EMCH-TFA additive improves the film morphology and passivates defects. • The addition of EMCH-TFA suppresses the formation of the small n phase. • The quasi-2D PeLED yields an EQE of 19.77 % and a current efficiency of 66.7 cd/A. • EMCH-TFA-treated MAPbI 3 -based PeSCs exhibits improved performance. Due to their unique quantum confinement, dielectric coupling, and tunable high-efficiency electroluminescence, quasi-two-dimensional (quasi-2D) perovskite light-emitting diodes (PeLEDs) have attracted considerable attention. However, imperfections in perovskite thin films introduced during the solution-based fabrication process lead to significant non-radiative recombination, hindering device performance. Addressing this challenge is crucial for realizing high-performance quasi-2D PeLEDs. In this study, we introduce an ion-pairing-type additive, 6-maleimidohexanehydrazide trifluoroacetate (EMCH-TFA), designed to cooperatively passivate defects in quasi-2D perovskites. The diverse functional groups (–COOH, –NH 2 , -CF 3) on EMCH-TFA could provide disparate modification to perovskite, among which the C O group tends to coordinate with the uncoordinated Pb2+ ions, thereby passivating the defects in the perovskite crystal. Additionally, the –NH 2 and -CF 3 groups establish hydrogen bonds with Br- ions and BA+ spacer cations, respectively. This multifaceted approach suppresses the formation of the small n phase and induces alterations in the crystalline state by interacting with numerous sites in perovskites, including A', B, and X sites. Consequently, the quasi-2D PeLED based on BA 2 Cs n-1 Pb n Br 3n+1 exhibits enhanced brightness, achieving a current efficiency of 66.7 cd/A and an impressive external quantum efficiency of 19.77 %. [ABSTRACT FROM AUTHOR]