Researchers at Nanjing Tech University (NanjingTech) and South China University of Technology have demonstrate a layer-by-layer (LBL) thermal-evaporation strategy to fabricate high-quality perovskite-emitting films with tunable emission wavelengths.
Schematic diagram of sequential thermal evaporation of perovskite thin films. Image credit: Nature Communications
Thermal-evaporated perovskite light-emitting diodes are highly promising for future display and lighting. However, current multi-source co-evaporation methods face challenges such as difficulty in regulating crystallinity, especially for red perovskite light-emitting diodes, whose external quantum efficiencies are still less than 2%.
In this recent work, the team used an LBL evaporation technique to sequentially deposit the organic halide formamidine hydroiodide (FAI), the metal halide CsBr, 5-aminovaleric acid (5-AVA) additive, and the metal halide lead iodide (PbI2) as the solid precursor. Through a subsequent post-annealing process, the scientists achieved the complete diffusion, reaction, and crystallization of the thin solid precursor layer (~50 nm) to form high-quality perovskite thin films. They noted that the introduction of 5-AVA could effectively suppressed in-situ interfacial reactions during vacuum deposition and slow down the crystallization process during post-annealing, significantly enhancing the crystalline quality of perovskite thin films. Additionally, 5-AVA could form coordination bonds with uncoordinated Pb²⁺, suppressing defect-induced non-radiative recombination.
The optimized emission film exhibited uniform optoelectronic properties with improved radiative recombination efficiency. As a result, the team achieved the efficient fully thermal evaporated red-PeLEDs (CsxFA1−xPbIyBr3−y), with a maximum EQE of 9% and a brightness exceeding 1500 cd m−2 (670 nm).
LBL evaporation allowed for continuous tuning of emission spectra by controlling the elemental ratios. The resulting deep-red PeLED (CsxFA1−xPbI3) showed an EQE of 7.27% (730 nm) and a high radiance of 204.71 W s−1 m−2.
Moreover, by taking advantage of the large-area uniformity of the sequential thermal evaporation, the scientists realized large-area (50 × 50 mm2) and patterned emissive thin films and devices.
This could provide a scalable and cost-effective approach for the production of high-performance PeLEDs, bridging the gap toward their commercialization in next-generation display and lighting technologies.
