Pure Deep Red Electroluminescence in Mixed Phase Quasi‐2D Tin Iodide Perovskite Heterostructure

Abstract Mixed cation quasi‐2D tin iodide perovskites are promising materials for deep‐red to NIR emitting light‐emitting diode (LED) applications. However, phase purity remains the major concern to avoid mixed emissions from two or more wavelengths. This work presents the evolution of pure deep red electroluminescence (EL) centred at ≈700 nm corresponding to the emission of pure n = 2 2D crystalline phase. However, structural and optical studies evidenced the formation of mixed‐phase heterostructures consisting of n = 1, n = 2, and n = ∞ phase (i.e., FASnI ₃ ). It is observed that altering the mixed cation ratio, phase distribution is modified, affecting the EL behavior, causing the observation or absence of the n = 1 2D phase EL emission peak. Selective charge transport and their cascade mechanism illustrates the pure color EL evolution with the support from transient absorption spectroscopic studies. In this regard, a case study is provided along with the supportive rationalities behind the exceptional evolution of pure deep red EL even from the mixed‐phase perovskite, reported for the first time in case of quasi‐2D tin iodide perovskite.