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

Abstract

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.