Unlocking High External Quantum Yield for Broadband Near-Infrared Emission From Lead-Free Perovskite Variant Solid Solutions Cs₂Te_1‒ _xMo_xCl₆.

Abstract

Broadband near-infrared (NIR) phosphor-converted LEDs are efficient light sources for imaging, sensing, and security. However, the development of NIR phosphors has been limited by a strategy that prioritizes internal quantum efficiency (IQE) while leaving absorption efficiency (AE) largely underexplored, causing the external quantum efficiency (EQE) to plateau. Here, we break from this convention and demonstrate an absorption-engineered, single-component solid solution, Cs₂Te_0.92Mo_0.08Cl₆, designed under a new strategy that synergistically optimizes AE and IQE. The material delivers broadband NIR emission spanning 750-1350 nm with an IQE of 97.4% and a record-high EQE of 65.6% for broadband NIR phosphors beyond 900 nm. This performance originates from the synergistic effect of strong photon harvesting, low phonon energy (138 cm^-1), and a Type-I band alignment, as confirmed by experimental and theoretical studies. Notably, Cs₂Te_0.92Mo_0.08Cl₆ maintains outstanding stability, enabling NIR LED fabrication on 395 nm UV chips. The fabricated device achieves a electro-optical conversion efficiency of 15.2% and an optical output of 112 mW, setting a new benchmark for NIR light sources. Practical demonstrations in ethanol concentration detection, solar energy harvesting, night vision, and anti-counterfeiting confirm its utility, thereby establishing a transformative design platform for next-generation optoelectronics.