In-situ molecular passivation enables pure-blue perovskite LEDs via vacuum thermal evaporation

(Press-News.org) Researchers report an in-situ passivation strategy for pure-blue perovskite light-emitting diodes (PeLEDs), promising for next-generation displays, fabricated by vacuum thermal evaporation. Co-evaporating a phenanthroline ligand (BUPH1) with perovskite precursors coordinates Pb(II) and suppresses halide-vacancy defects, reducing non-radiative losses and spectral drift.  Their work is published in the journal Industrial Chemistry & Materials on August 25.

Metal halide perovskites are rapidly emerging as candidates for the next generation of displays thanks to their narrow emission linewidths, tunable bandgaps, high photoluminescence quantum yields, and compatibility with scalable manufacturing. Unlike many solution-processed emitters, perovskites can be vacuum-thermally evaporated on the same toolsets used for OLED production, enabling precise thickness control, fine patterning, uniform films, and fully dry processing—key requirements for industrial adoption.

Within this landscape, pure-blue emission is particularly prized for wide-gamut, high-definition displays. The Rec.2020 blue point lies near 468 nm in the CIE 1931 space, placing the 460–475 nm window in an optimal range for vivid color without the eye fatigue often associated with deeper blue (<460 nm) or the washed-out appearance of sky blue (>475 nm). Yet this region is challenging: higher Cl/Br ratios can trigger phase segregation and spectral drift, and the human eye’s lower sensitivity here tends to depress apparent brightness. In vacuum-processed perovskites, unsaturated Pb(II) defects formed under halide-deficient conditions further act as non-radiative centers that erode efficiency.

The team addresses these bottlenecks with an in-situ passivation approach during vacuum thermal evaporation. A phenanthroline-based small molecule, BUPH1 (4,7-di(9H-carbazol-9-yl)-1,10-phenanthroline), is co-evaporated with the perovskite precursors so that, as the film grows, BUPH1’s nitrogen lone pairs coordinate Pb(II) and passivate halide-vacancy defects, helping to suppress ion migration without extra processing steps. In parallel, the halide composition is precisely tuned by co-evaporating lead(II) bromide (PbBr2), cesium chloride (CsCl), and cesium bromide (CsBr) to target the pure-blue window.

“As perovskites compatible with vacuum thermal evaporation are compelling for next-generation displays, low efficiency has remained a persistent bottleneck,” said Byungha Shin, corresponding author and professor at the Korea Advanced Institute of Science and Technology (KAIST). “By passivating under-coordinated Pb(II) during growth, we identify a practical path toward overcoming that hurdle—achieving color-stable pure-blue emission while staying aligned with industry-standard fabrication.”

As a result, the devices emit at 472 nm with a 19 nm FWHM and reach an EQE of 3.1%, among the highest reported for thermally evaporated pure-blue PeLEDs to date. Importantly, the emission remains color-stable under electrical bias, supporting Rec.2020, the ITU-R wide-gamut UHDTV standard. Because the strategy is compatible with mainstream OLED-class vacuum tools, it offers a practical route toward industrially relevant, high-color-purity blue pixels.

Looking ahead, the team will pursue additional passivation strategies to further raise luminance and extend operational lifetime, with the goal of fully thermally evaporated device stacks suited for manufacturing. 

The research team includes Jiyoung Kwon, Yunna Kim, Nakyung Kim, Jinu Park, Sukki Lee, Seoyeon Park, and Byungha Shin from KAIST, and Sunwoo Kang from Dankook University. This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT).

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. ICM publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials. Check out the latest ICM news on the blog.

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