Enhancing Sky-Blue Perovskite Light-Emitting Diode Performance through Guanidinium-Based Dual-Functional Molecular Engineering

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for next-generation display and lighting technologies due to their high photoluminescence quantum yield, tunable emission characteristics, and narrow spectral bandwidth. However, achieving efficient and stable blue emission remains a significant challenge, primarily due to poor phase purity, excessive trap density, and unfavorable energy level alignment. Herein, we propose a dual-functional molecular engineering strategy utilizing 4-guanidinobenzoic acid hydrochloride (GBAC) as both a buried interfacial layer and a bulk additive. When employed at the buried interface, GBAC enhances surface wettability and precursor spreading, thereby improving film morphology and crystallinity. This additional layer also helps optimize energy level alignment between the hole transport layer and the perovskite emissive layer, reducing the injection potential barrier. Simultaneously, when acting as an additive in the bulk phase, GBAC's guanidinium group binds to undercoordinated Pb²⁺ trap states via electrostatic coordination, suppressing nonradiative recombination; while its carboxylic group forms hydrogen bonds with the ammonium end of phenethylammonium bromide, reducing the formation of low-<i>n</i> (<i>n</i> = 1-2) phases and promoting growth in the medium-to-high n-value domains, thereby enhancing energy funneling efficiency. Leveraging these advantages, the device fabricated with dual GBAC treatment exhibits enhanced spectral stability, reduced turn-on voltage, and achieves an external quantum efficiency of up to 10.6% in the sky-blue emission band (∼489 nm), representing <i>a</i> > 60% improvement over the pristine device.