Weakly Confined Perovskite Nanocrystal Films for Energy-Efficient Electroluminescence Devices.

High wall-plug efficiency (WPE) and long-term operational stability are major hurdles for perovskite light-emitting diodes (PeLEDs) toward low-power practical applications. This work presents high-WPE PeLEDs utilizing in situ fabricated weakly confined perovskite nanocrystal films with boosted stability. Reducing the proportion of bulky organic cations increases the nanocrystal size, causing a red-shift of the emission peak. A small-molecule salt is further introduced to regulate crystallization, reducing surface trap-state density and electron-phonon coupling strength. The resulting weakly confined nanocrystal films retain high WPE and an ultranarrow emission line width, while showing markedly better thermal and structural stability. Optimized device achieves a low turn-on voltage of 1.8 V, a peak WPE of 28.7%, and an ultranarrow electroluminescence line width of 17.6 nm. Notably, the device exhibited a T50 operational lifetime exceeding 10,000 h at 100 cd m-2. This study proves weakly confined perovskite nanocrystal engineering can synergistically enhance efficiency, stability, brightness and color purity, providing a feasible route to high-performance PeLEDs.