Optimized Photoemission from Organic Molecules in 2D Layered Halide Perovskites

In recent years, hybrid organic-inorganic metal halides have been at the forefront of materials research. Typically, the functional (e.g., optoelectronic) properties of hybrid halides are derived from the inorganic structural part, whereas the organic structural units can add extra advantages in terms of stability, rigidity, and processability. Here, we report the design, synthesis, and characterization of two new hybrid materials in which the outstanding photophysical properties originate from the organic structural part. The new compounds, (C₁₅H₁₆N)₂CdCl₄ and ((Br)C₁₅H₁₅N)₂CdCl₄, have 2D layered Ruddlesden-Popper-type perovskite structures. These hybrids are blue-white light emitters just like their corresponding pure organic salts, but with much improved emission efficiencies. Optical spectroscopy and density functional theory (DFT) studies confirm that photoemission comes from the trans-stilbene organic cations. The photoluminescence quantum yield (PLQY) values of these new materials are among the highest known, 50.83% and 26.60% for (C₁₅H₁₆N)₂CdCl₄ and ((Br)C₁₅H₁₅N)₂CdCl₄, respectively. This is up to a 5-fold increase as compared to the light emission efficiency of the precursor salt C₁₅H₁₆NCl (PLQY of 10.33%). Alongside their outstanding optical properties, their environmental and thermal stability allow their consideration for potential practical applications such as radiation detection. This work shows that hybrid metal halides can be compositionally and structurally engineered to have highly efficient photoemission originating from the organic components for fast scintillation applications.