<p>Lead halide perovskites hold great promise for a wide range of applications owing to their exceptional characteristics. Nevertheless, the inherent toxicity of lead and poor stability concerns considerably restrict their real-world use. Although lead-free halide perovskites reduce toxicity, they experience a substantial decrease in photoluminescence quantum yield (PLQY). To tackle these challenges, Cs₃Cu₂I₅ nanocrystals (NCs) were initially synthesized via a one-step ultrasonic method, followed by the use of amphoteric polymer polyethylene glycol-polycaprolactone (PEG-PCL) to coat the Cs₃Cu₂I₅ NCs, resulting in Cs₃Cu₂I₅/PEG-PCL composites that exhibited a remarkable improvement in stability and PLQY (~ 74.7%). Several characterization techniques were utilized to confirm the successful formation of the perovskite composites and explore the reasons for its high performance.&#xa0;The enhancement in PLQY may be primarily attributed to the passivation effect of PEG on the perovskite. The synthesized composites were then employed for the construction of a highly sensitive fluorescence sensor for H₂S detection, achieving a detection limit as low as 0.70 µmol/L. This study not only offers a novel strategy for enhancing the PLQY of lead-free halide perovskite materials but also demonstrates their promising application in food analysis.</p> Graphical Abstract <p></p>