Effective passivation of perovkiste grain boundaries by a carboxylated polythoiphene for bright and stable Pure-Red perovskite light emitting diodes

High luminance and operative stability are essential parameters for realizing the commercialization of perovskite-based light-emitting diodes (PLEDs). However, the optoelectronic properties of PLEDs are still limited owing to the un-optimized charge transport behavior of perovskite films arising from severe defect densities and imperfect lattice structure at grain boundaries. To retrieve the morphological imperfection, we herein suggest a carboxylated polythiophene (P3CT) as a novel passivating agent of perovskite films in PLEDs. The carboxylic acid groups of P3CT enable Lewis acid-base interactions with the defective surface of perovskites such as under-coordinated Pb²⁺ sites or halide deficiencies, leading to efficient defect passivation and stabilization of the perovskite film surface. The P3CT-passivation successfully fabricates pinhole-free perovskite films with diminished defects at grain boundaries, bringing enhanced optoelectronic properties of red electroluminescence EL emission with a peak current efficiency and external quantum efficiency (EQE) values up to 11.15 % and 4 %, respectively. Moreover, the operative stability of the passivated PLEDs is markedly improved due to the stabilization and increased hydrophobicity of perovskite films by the inclusion of P3CT. The present findings provide a new perspective for developing stable red-PLEDs with efficient luminescence.