Complementary Advantages: Construction of Rare‐Earth‐Free Sunlight Conversion CsMnCl₃(H₂O)₂/Cs₃SbCl₆ Heterojunction for Energy‐Saving Agricultural Cultivation

Abstract Development of efficient sunlight conversion materials is critical for advancing sustainable agricultural practices, but current solutions often face challenges such as poor stability, high cost, and reliance on rare‐earth elements. This study presents a rare‐earth‐free xCsMnCl 3 (H 2 O) 2 /(1−x)Cs 3 SbCl 6 heterojunction ( x = 1−0.65) synthesized via an eco‐friendly mechanochemical method. By strategically combining Cs 3 SbCl 6 as a UV‐absorbing donor with CsMnCl 3 (H 2 O) 2 as an efficient red emitter. The optimized heterojunction achieves a remarkable 36‐fold enhancement at 626 nm (Full width at half maxima (FWHM) = 88 nm), perfectly matching chlorophyll a's absorption spectrum. Comprehensive experimental and theoretical analyses, including UV–vis absorption, photoluminescence (PL) spectroscopy, and density functional theory (DFT) calculations, reveal a dual enhancement mechanism: i) efficient interfacial electron‐hole transfer and ii) suppression of non‐radiative recombination through defect passivation. The practical application is demonstrated through a sunlight conversion film fabricated by embedding the 0.75CsMnCl 3 (H 2 O) 2 /0.25Cs 3 SbCl 6 composite in Ecoflex‐0030, which exhibits exceptional environmental stability (90% PL retention after 90 days) and mechanical durability (500% tensile strain). The plant growth experiments confirm the film's agricultural efficacy, with chives and green cabbage growth rates increasing by 1.5‐ and 1.3‐fold, respectively, compared to natural light conditions. This work not only addresses the limitations of existing light‐conversion materials but also establishes a rare‐earth‐free, eco‐friendly platform for energy‐efficient agriculture.