Azetidinium as cation in lead mixed halide perovskite nanocrystals of optoelectronic quality

Previous theoretical calculations show that azetidinium has the right radial size to form a 3D perovskite with lead halides [G. Kieslich et al., Chem. Sci. 5, 4712 (2014)] and has been shown to impart, as the A-site cation of the ABX3 unit, beneficial properties to ferroelectric perovskites [B. Zhou et al., Angew. Chem., Int. Ed. 50, 11441 (2011)]. However, there has been very limited research into its use as the cation in lead halide perovskites to date. In this communication, we report the synthesis and characterization of azetidinium-based lead mixed halide perovskite colloidal nanocrystals. The mixed halide system is iodine and chlorine unlike other reported nanocrystals in the literature, where the halide systems are either iodine/bromine or bromine/chlorine. UV-visible absorbance data, complemented with photoluminescence spectroscopy, reveal an indirect-bandgap of about 2.018 eV for our nanocrystals. Structural characterization using transmission electron microscopy shows two distinct interatomic distances (2.98 Å ± 0.15 Å and 3.43 Å ± 0.16 Å) and non-orthogonal lattice angles (≈112°) intrinsic to the nanocrystals with a probable triclinic structure revealed by X-ray diffraction. The presence of chlorine and iodine within the nanocrystals is confirmed by energy dispersive X-ray spectroscopy. Finally, light-induced electron paramagnetic resonance spectroscopy with PCBM confirms the photoinduced charge transfer capabilities of the nanocrystals. The formation of such semiconducting lead mixed halide perovskites using azetidinium as the cation suggests a promising subclass of hybrid perovskites holding potential for optoelectronic applications such as in solar cells and photodetectors.