MASnI3

MASnI3, or methylammonium tin iodide, is an organic–inorganic lead-free perovskite with the chemical formula CH3NH3SnI3. It belongs to the ABX3 family of perovskites, where the A-site is the methylammonium cation (MA+), B-site is tin in the +2 oxidation state, and X-site is iodide. MASnI3 has attracted interest as a potential alternative to lead-based perovskites for photovoltaic and optoelectronic applications due to its tunable optical properties and reduced toxicity concerns.

The material adopts the characteristic perovskite structure, comprising corner-sharing SnI6 octahedra with MA+ cations occupying interstitial sites. This framework yields a direct bandgap, typically in the vicinity of 1.2 to 1.3 eV, which is favorable for light absorption and solar energy conversion. The electronic and structural properties are sensitive to temperature, composition, and synthesis conditions, and tin-based perovskites often show different phase behavior compared with their lead counterparts.

Fabrication of MASnI3 thin films commonly uses solution-processing techniques such as spin coating under inert atmosphere, with strategies to mitigate tin(II) oxidation. Additives like SnF2 and partial substitutions or mixed-cation/halide approaches are employed to improve film quality and stability. Processing challenges include controlling Sn2+ to Sn4+ oxidation, rapid crystallization, and moisture sensitivity, all of which can introduce deep defects and hinder device performance.

Stability is a major limitation for MASnI3. Exposure to air, oxygen, and moisture promotes Sn2+ oxidation to Sn4+, creating defects that trap charge carriers and cause rapid degradation. Encapsulation, reducing environments, and chemical engineering of the composition are active research areas aimed at extending device lifetimes.

Applications of MASnI3 focus on solar cells and photodetectors, with ongoing work to enhance efficiency and longevity. While record performance lags behind lead-based perovskites, MASnI3 remains a candidate for lead-free tandem cells and sustainable optoelectronic devices.