Correlated optical and ionic transport signatures of photoactivated defects in Cs3Bi2Br9 single crystals
摘要
A comprehensive electrical, vibrational and optical investigation of the Cs3Bi2Br9 single crystals emphasizes their unique light-responsive behavior. Strong electron–phonon coupling and thermally-activated exciton delocalization are shown through a narrowing of the full width at half maximum (FWHM) from 0.080 to 0.063 eV while, with an emission peak shifting from 2.48 eV at 77 K to 2.53 eV at 300 K, the broad self-trapped exciton emission is revealed by temperature-dependent photoluminescence (PL). A redshift of ~ 0.005–0.015 eV and a pronounced photoluminescence quenching exceeding 50% are demonstrated under continuous illumination. This agrees with the negative photoconductivity-like behavior concluded from photoluminescence quenching. With systematic redshifts of up to ~ 1.3 cm−1, the light-induced phonon softening and the linewidth broadening associated with Vk centers and lattice distortions are revealed by Raman spectroscopy. With an activation energy declining in the dark from ~ 220 meV to ~ 180 meV under illumination, the electrochemical impedance spectroscopy indicates illumination-enhanced ionic transport to a greater degree. Therefore, the ionic mobility rises to ~ 5 × 10−8 cm2·V−1 s−1 at 400 K, whereas the ionic diffusion coefficient reaches up to 3.9 × 10−13 m2 s−1. This material is established as a promising lead-free platform for light-responsive optoelectronic applications since this work is a rare and quantitative demonstration of light-accelerated ion dynamics in bulk Cs3Bi2Br9, to the best of our knowledge.