Effect of Monovalent Metal Iodide Additives on the Optoelectric Properties of Two-Dimensional Sn-Based Perovskite Films

The application of organic–inorganic perovskites has recently attracted increasing interest due to their excellent optoelectronic properties. As an emerging semiconductor, the doping capability and efficiency of these materials require further clarification but have rarely been studied previously. In this study, diverse monovalent cations, Cu⁺, Na⁺, and Ag⁺, are incorporated into phenethylammonium tin iodide ((PEA)₂SnI₄) perovskite, and the resultant lattice structural variation, film properties, and thin-film transistor performance are systematically investigated by combining theoretical and experimental methods. Owing to their unique composition and octahedral unit, perovskite semiconductors possess strong ‘substitution doping tolerance’ with the aliovalent cation dopants. Theoretical studies claim that the hypothetical monovalent cation substitution on the Sn²⁺ B-site creates undesired vacancies and destabilizes the perovskite lattice structure. The experimental results show that the incorporated foreign aliovalent cations are not doped inside the perovskite lattice but segregated along the grain boundaries. Benefiting from the excellent hole transport property and passivation effect of copper iodide (CuI), the CuI–(PEA)₂SnI₄ heterostructure composite channel layers exhibit much improved film properties and device performance, including doubled field effect mobility, compared with the pristine ones.