Stabilized photoemission from organic molecules in zero-dimensional hybrid Zn and Cd halides

Abstract

This work explores the utilization of a photoactive organic cation for the preparation of R₂MCl₄ (M = Zn, Cd; R = (E)-4-styrylpyridinium, C₁₃H₁₂N⁺). The zero-dimensional crystal structures of R₂MCl₄ contain isolated tetrahedral anions [MCl₄]²⁻ separated by the organic cations R⁺, leading to flat bands around the optical band gap. In R₂MCl₄, the inorganic band gaps are sufficiently large to accommodate the organic molecular levels within, and therefore, the optical properties of R₂MCl₄ are determined by the organic cation. Our combined optical spectroscopy and density functional theory (DFT) studies confirm the attribution of the bright green photoluminescence demonstrated by R₂MCl₄ to the organic molecular emission. Importantly, the incorporation of the photoemissive organic cation R⁺ into the hybrid framework in R₂MCl₄ leads to a nearly two-fold enhancement of the light emission efficiency with the measured photoluminescence quantum yield (PLQY) values of 6.04%, 10.40% and 11.21% for RCl, R₂ZnCl₄ and R₂CdCl₄, respectively. In addition, the crystal structure of the hybrid R₂MCl₄ ensures a stabilized PL emission, preventing the occurrence of the harmful organic photodimerization, which is a notorious problem for this class of organic emitters.