Crystal Facet Engineering in Thermally Evaporated Ytterbium-Doped Perovskite Near-Infrared Light-Emitting Diodes

Quantum-cutting CsPbCl 3:Yb perovskites represent a compelling class of emitters for high-performance near-infrared (NIR, >950 nm) light-emitting diodes (LEDs). The intrinsic anisotropy in dielectric response, surface termination chemistry, and strain fields across different crystallographic facets significantly influences perovskite optoelectronic performance. However, precise control over facet-selective growth in CsPbCl 3:Yb thin films remains challenging due to pronounced disparities in surface and formation energies. Here, we introduce a thermal evaporation strategy to achieve controlled crystallographic orientation of CsPbCl 3:Yb films for enhanced NIR emission. By modulating thermodynamic and kinetic processes, we enable selective growth of (100)- and (110)-oriented films. Comparative analysis reveals that (110)-oriented films provides a more favorable dielectric environment, resulting in stronger exciton binding and enhanced energy transfer to Yb 3+ ions. Leveraging this facet-guided design, our optimized device delivers an external quantum efficiency (EQE) of 7.05% and a radiance of 639 mW/sr/m 2 for vacuum-processed NIR (>950 nm) LEDs.