Researchers from Hebei University of Technology, the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences, and the Chinese University of Hong Kong have developed a fabrication method for perovskite light-emitting diodes (PeLEDs) that works entirely in open air, lifting the photoluminescence quantum yield (PLQY) of the emissive film from 6% to 64% and yielding devices with a peak external quantum efficiency (EQE) of 10.5% and an operational lifetime of 125.6 minutes.
PeLEDs are attractive for next-generation displays and lighting thanks to their narrow emission linewidths, high color purity and solution processability, and devices spanning blue, green, red and near-infrared have already achieved EQEs above 20%. However, perovskite films are highly sensitive to atmospheric moisture and oxygen, which normally forces fabrication into tightly controlled inert atmospheres - adding cost and complexity that stands in the way of scaling the technology up commercially. One common workaround adds hydrophobic organic ammonium halides to the perovskite precursor, which induce quasi-2D structures that confine excitons and make the film more moisture-tolerant. But conventional versions of this approach, built on hydrophobic long-chain ligands, bring their own problems: the ligands' bulk widens the spacing between quantum wells in a way that hampers carrier injection and interlayer energy transfer, and ligand aggregation tends to produce an excess of low-n phases that introduce additional non-radiative recombination. Producing well-regulated quasi-2D films has also typically required precisely controlled antisolvent dripping using toxic, volatile solvents such as diethyl ether or chlorobenzene - a process sensitive to timing, solvent diffusion and humidity, giving a narrow processing window and poor reproducibility, especially in ambient conditions.
The team's alternative combines two elements. The first is vacuum flash-assisted solution processing (VASP), a technique already used to control crystallization in perovskite solar cells but rarely applied to PeLED emissive layers. Lowering the pressure around the wet precursor film reduces the boiling point of the residual solvent, allowing it to be extracted quickly and promoting uniform nucleation across the film, without the liquid-liquid diffusion step that antisolvent methods rely on. In this process, a CsPbBr3 precursor solution is spin-coated in air, the wet film is transferred to a flash evaporator to rapidly remove residual solvent, and the film is then exposed to ambient air at 20-40% relative humidity, promoting room-temperature crystallization and grain growth without antisolvents or thermal annealing.
The second element is guanidinium bromide (GABr), added into the CsPbBr3 precursor as a spacer cation. The GA+ cations form hydrogen bonds with perovskite intermediates, moderating crystal growth and helping produce compact, high-quality films, while the lone-pair electrons on GA+'s amino and imino groups coordinate with undercoordinated Pb2+ sites, suppressing non-radiative recombination centers. By tuning the GABr concentration, the team produced compact, localized quantum-well structures that confine excitons effectively while still allowing efficient energy transfer between wells and charge transport through the film - avoiding the wide well-spacing and excess low-n phase problems of conventional long-chain-ligand additives.
Combining VASP-driven crystallization with GABr-mediated defect passivation raised the film's PLQY from 6% to 64%, and PeLEDs built from these ambient-processed films reached a peak EQE of 10.5% with an operational lifetime of 125.6 minutes - demonstrating, according to the researchers, a viable route to fabricating high-performance perovskite LEDs entirely in air.
