Tribenzyl Organic Cations Carried Multidentate X-Type Lewis Soft Base for High-Performance Foldable Perovskite Light-Emitting Diodes

Lead-halide perovskite nanocrystals (PNCs) exhibit significant potential for advancing foldable perovskite light-emitting diodes (F-PLEDs) due to their discrete crystalline morphology, bright emission across an extensive color gamut, and remarkable color purity; however, their progression remains in the early stages with the concerns of inadequate performance and mechanical instability. This study proposes a ligand strategy employing tribenzyl organic cation (tribenzylamine, TBA) carried multidentate X-type Lewis soft base (sodium acid pyrophosphate, SAPP) to address the challenges above simultaneously. Specifically, the use of multibranched aromatic ligands considerably improved the adhesion force between PNCs and adjacent layers, enhancing mechanical stability during folding, while the control sample shows deleterious cracks. Additionally, TBA-SAPP ligands effectively eliminate the defects in PNC film, yielding exceptional photoluminescence properties with a near-unity quantum yield. Consequently, the multifunctional ligands improved F-PLEDs to achieve a record-high external quantum efficiency (EQE) of 16.2% compared to the previously reported pure-red flexible PLEDs and display substantially improved spectral and operational stability. Equally important, these devices demonstrate robust mechanical properties, enduring a small folding radius of 1 mm for 5000 cycles. This ligand strategy is anticipated to inspire relevant research in PNCs and promote the realization of highly efficient and mechanically stable F-PLEDs.