Photoresponsive Charge-Lattice Interplay in Layered Lead-Free Cs₃Sb₂Cl₉ Perovskite Crystals

The search for stable, nontoxic alternatives to lead-based halide perovskites has directed significant attention toward the Cs₃Sb₂Cl₉ compound, a promising lead-free material with a layered crystal structure. In this study, we comprehensively investigate the structural, thermal, optical, vibrational, and electrical properties of high-quality Cs₃Sb₂Cl₉ single crystals. X-ray diffraction (XRD) analysis confirms the formation of a well-crystallized trigonal phase (P-3m1), with lattice parameters consistent with prior reports. Thermogravimetric analysis (TGA) reveals thermal stability up to 321 °C. Optical absorption measurements reveal an indirect bandgap of 2.76 eV and an Urbach energy of 0.37 eV, indicating moderate static disorder and exciton-phonon coupling within the layered 2D framework. Photoluminescence (PL) spectra under dark and illuminated conditions exhibit pronounced intensity enhancement and redshift upon photoexcitation, supported by Voigt profile analysis revealing reduced line widths under illumination. Raman spectroscopy reveals characteristic vibrational modes associated with Sb-Cl bonding, with illumination inducing spectral sharpening and enhanced mode intensities, indicative of dynamic lattice stabilization. Electrochemical impedance spectroscopy (EIS) highlights improved charge transport and reduced recombination losses under illumination, supported by decreased activation energies and suppressed ionic diffusion. These findings reveal a strong interplay between light exposure and charge-lattice dynamics, demonstrating Cs₃Sb₂Cl₉'s potential for optoelectronic applications where environmental stability and photophysical responsiveness are critical.