Balancing Structural Properties to Improve Quantum Yields in Zinc‐Based Halometallate Films

Lead halide perovskites are highly sought after for optoelectronic applications due to their tunable bandgaps and high quantum yields. However, concerns regarding lead toxicity and stability have driven research toward alternative materials, such as organic–inorganic metal halides or halometallates. Among these, low‐dimensional, zero‐dimensional structures show significant promise. Zinc has emerged as an abundant, low‐cost, nontoxic candidate to replace lead, particularly for blue light emission. While previous studies focused on nonconjugated organic cations yielding “ultrastable” materials, this article investigates the impact of using light‐absorbing, conjugated organic cations instead. The optical properties of 15 different conjugated materials were studied in both the solution phase and as thin films. By varying naphthalimide isomers with piperidinyl organic pendants having different cation steric bulk and anion size, the study examines emissive properties in spin‐coated amorphous Zn‐based OIMH films to show that photoluminescence efficiency in these materials can be improved, ultimately leading to films with PLQYs of up to 29% of an HCl salt of the organic cation and 26% for one of the hybrid materials.