Device performance improvements in all-inorganic perovskite light-emitting diodes: the role of binary ammonium cation terminals

Abstract

All-inorganic perovskites, like CsPbBr₃, have gained particular concern due to their excellent material stability. However, aside from the general defect issue in perovskite materials, all-inorganic perovskites also suffer from poor film quality, leading to low device efficiency, especially of perovskite light-emitting diodes (PeLEDs) employing a thin perovskite film as the emission layer. Herein, 1,4-phenyldimethylammonium dibromide (phDMADBr), which has ammonium cations (NH₃⁺) on both terminals, is introduced as the additive in the precursor solution. It is proved that phDMADBr can improve the film coverage; meanwhile, it also presents a more intense passivation effect on point defects than a similar additive with a single NH₃⁺ terminal. As demonstrated by density functional theory (DFT) calculations, phDMADBr tends to anchor onto the Br-dangling bond with both NH₃⁺ tails and enhances the adhesion to the perovskite grain surface. The exposed hydrophobic aryl also protects the perovskite from detrimental environmental factors. Correspondingly, the maximum luminance (L_max), current efficiency (CE), and device stability of the PeLEDs are enhanced. This work offers special guidance for screening passivation additives for inorganic perovskites.