Structural and Optical Investigations of Quasi-0D Lead-Free Hybrid Halide Crystals: (C6H16N)2ZnI4 and (C6H16N)2CdI4

With excellent optoelectronic behavior, organic-inorganic hybrid perovskites have become leading contenders in the development of future photovoltaic and optoelectronic devices. Herein, two new lead-free, quasi-0D OIHPs, (C 6 H 16 N) 2 ZnI 4 and (C 6 H 16 N) 2 CdI 4 , are synthesized, and both crystallize in the monoclinic system (P2 1 /n space group) as confirmed via single-crystal X-ray diffraction analysis. Optical bandgaps are measured to be 4.595 eV for (C 6 H 16 N) 2 ZnI 4 and 4.255 eV for (C 6 H 16 N) 2 CdI 4 , which align well with those from first-principles calculations. Photoluminescence studies on (C 6 H 16 N) 2 ZnI 4 and (C 6 H 16 N) 2 CdI 4 show peaks at 393 and 382 nm, respectively, which are attributed to self-trapped exciton (STE) transitions induced by lattice distortion. Notably, (C 6 H 16 N) 2 CdI 4 exhibits unusual blue emission (quantum yield: 1.41%, lifetimes: 168.5 ps), while (C 6 H 16 N) 2 ZnI 4 shows blue luminescence with enhanced efficiencies (quantum yields: 19.64%, lifetimes: 473.7 ps). These findings broaden the application prospects of 0D OIHP materials in renewable energy and photonics.