CTAB-assisted surface passivation of lead-free Cs2AgBiCl6 double perovskite for defect suppression and enhanced photophysical properties

Lead-free halide perovskites have attracted significant attention as environmentally friendly alternatives to lead-based perovskites, owing to their low toxicity and tunable electronic and optical properties, which offer potential for diverse optoelectronic and sensing applications. In this study, we report the synthesis of the lead-free halide double perovskite Cs 2 AgBiCl 6 and the cationic surfactant cetyltrimethylammonium bromide (CTAB)- passivated CTAB@Cs 2 AgBiCl 6 . Structural, morphological, and optical studies confirmed the successful incorporation of CTAB without altering the structural properties. The CTAB@Cs 2 AgBiCl 6 exhibited improved crystallinity, larger grain size, an enhanced average carrier lifetime from 3.20 ns to 17.86 ns, and greater water stability than the pristine material, indicating defect passivation and improved photophysical properties. The CTAB-modified sample shows a slightly reduced optical bandgap of 2.47 eV, compared with 2.55 eV for pristine Cs 2 AgBiCl 6 . We further performed DFT calculations on pristine Cs 2 AgBiCl 6 and CTAB@Cs 2 AgBiCl 6 to provide theoretical insight into the experimental observations. These findings show that CTAB modification significantly improves the optical performance and environmental stability of Cs 2 AgBiCl 6 , highlighting its potential for future lead-free optoelectronic and sensing applications.