Unveiling the Role of Additive Molecular Characteristics in Regulating Chlorine Loss and Phase Distribution for Blue Perovskite Light‐Emitting Diodes

Abstract Perovskite light‐emitting diodes (PeLEDs) have garnered extraordinary attention in displaying field owing to their excellent luminescence properties. Although exogenous additives are extensively employed for optimizing PeLEDs, their comprehensive regulation including side effects still lacks in‐depth study. Here for the first time, it is demonstrated that the deprotonation degree of additives significantly influences the performance of blue PeLEDs. Benzenesulfonic acid (BSA) and ammonium benzenesulfonate (ABS) with similar molecular structures while distinctly different acid dissociation constants (pK_a) are used for modifying blue perovskites. By comparison, high‐pK_a ABS holds greater potential in boosting device performance, contributing to an improved peak external quantum efficiency of 18.8%. This discrepancy is ascribed to the fact that low‐pK_a BSA is prone to induce prominent perovskite chlorine loss owing to its intense deprotonation, while high‐pK_a ABS significantly suppresses chlorine vacancy formation. Meanwhile, the adsorption energy of organic spacer onto perovskite is greatly reduced due to the strong intermolecular hydrogen bonding with ABS, contributing to a concentrated phase arrangement for smooth exciton energy transfer. Additionally, ABS modification further suppresses trap‐mediated nonradiative recombination by coordinating with the undercoordinated lead (II) ions at grain boundaries. This work provides valuable guidelines for optimizing additive screening toward high‐performance blue PeLEDs.