Hypophosphite-assisted ball milling enables broadband self-trapped exciton emission in copper halides for self-powered smart windows.

Metal halide perovskites have shown remarkable potential in photovoltaic and optoelectronic applications due to their excellent light absorption, high defect tolerance, and long carrier diffusion lengths. In this study, we systematically investigate copper-based metal halides and introduce a hypophosphorous acid-assisted mechanochemical ball milling strategy to construct highly stable copper halide systems. Leveraging the broadband emission characteristics of self-trapped excitons (STE), we explore the controlled synthesis and optoelectronic applications of these materials. Using DPCu4Br6 (DP = p-phenylenediamine) as a representative compound, we achieved outstanding optical performance, including broadband emission (FWHM = 120 nm), minimal reabsorption, ultrahigh photoluminescence quantum yield (PLQY = 98.38%), and a long exciton lifetime of 47.62 µs. Remarkably, the material retained over 80% of its PLQY after six months of exposure to ambient air, demonstrating superior environmental stability. Based on these results, a 6 × 6 cm2 luminescent solar concentrator (LSC) was fabricated, achieving an optical conversion efficiency (η opt) of 12.43%, and successfully integrated with electrochromic smart windows to enable self-powered light modulation through a synergistic system design.