Synthesis and Characterization of CH3NH3SnI3 and CH3NH3SnICl2 Tin-Based Halide Perovskite Films

In this study, hybrid tin-based perovskite films of CH3NH3SnI3 and CH3NH3SnICl2 were synthesized and systematically characterized to evaluate the influence of partial halide substitution. Atomic Force Microscopy (AFM) and Optical Microscopy (OM) revealed that chloride incorporation improves surface uniformity and increases grain size. X-ray diffraction (XRD) analysis showed that CH3NH3SnI3 contains the expected tetragonal perovskite phase together with minor secondary phases. Fourier Transform Infrared Spectroscopy (FTIR) confirmed characteristic CH3NH ₃⁺ vibrational modes with slight shifts resulting from lattice modification induced by halide substitution. UV–V is absorption measurements revealed tunable optical properties, with a band gap of 1.35 eV for CH3NH3SnI3 and 1.55 eV for CH3NH3SnICl2. Photoluminescence (PL) spectra showed stronger and narrower emission for CH3NH3SnICl2 (~820 nm) compared to CH3NH3SnI3 (~920 nm), indicating reduced trap-state density and improved radiative recombination. The novelty of this work lies in the direct comparative analysis of nanoscale CH3NH3SnI3 and mixed-halide CH3NH3SnICl2 films synthesized under identical conditions, demonstrating that partial I– → Cl– substitution significantly improves structural quality, optical performance, and stability. These findings identify CH3NH3SnICl2 as a promising lead-free candidate for next-generation optoelectronic and photovoltaic devices.