Efficient All-Inorganic Perovskite Light-Emitting Diodes with Improved Operation Stability

Area of Science:

• Materials Science
• Optoelectronics
• Solid-State Chemistry

Background:

• Perovskite light-emitting diodes (PeLEDs) show promise, but stability remains a critical challenge despite high external quantum efficiencies (EQEs).
• All-inorganic cesium lead iodide (CsPbI3) offers better stability than hybrid counterparts but is prone to phase transitions.
• The desirable α-CsPbI3 phase is unstable at room temperature, transitioning to a non-emissive yellow δ-phase.

Purpose of the Study:

• To stabilize the α-CsPbI3 phase for improved PeLED performance and longevity.
• To develop a method for creating stable, nanostructured CsPbI3 films for emissive layers.
• To investigate the impact of bulky organoammonium halides on CsPbI3 phase stability and device characteristics.

Main Methods:

• In situ formation of perovskite nanocrystals (NCs) within a CsPbI3 matrix.
• Incorporation of 4-fluoro-phenylmethylammonium iodide (4-F-PMAI) at a specific ratio.
• Fabrication of stable α-CsPbI3 films using a one-step spin-coating technique.

Main Results:

• Stable α-CsPbI3 films with nanometer-sized crystals were successfully obtained.
• PeLEDs utilizing these films exhibited pure red emission at 692 nm with a high EQE of 14.8%.
• EQE was further enhanced to 18.6% by using a CsPbI2.8Br0.2 emissive layer, alongside improved device lifetime (>1200 min) and shelf stability (>2 months).

Conclusions:

• The in situ formation of CsPbI3 NCs, stabilized by 4-F-PMAI, effectively prevents phase transitions.
• This approach yields highly stable red-emitting PeLEDs with competitive EQEs and significantly enhanced operational and shelf lifetimes.
• The developed method offers a viable strategy for advancing stable and efficient perovskite optoelectronic devices.