Abstract
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.
Highlights
Organic/inorganic lead halide perovskites (LHPs), using earthabundant elements, have shown tremendous potential in achieving lab-scale efficiencies of solar cells approaching that of the crystalline silicon solar cells.1 The current high-performing LHPs are composed of methylammonium (MA), formamidinium (FA), and caesium (Cs) as the A-site cations in ABX3, which form a 3D structure
Our work has shown the suitability of azetidine in forming perovskite-type NCs with lead iodide and revealing properties with the potential for optoelectronic applications
This points toward the formation of lead mixed halide perovskites with chlorine and iodine observed for the first time in NCs, and not seen before with Cs, MA, or FA cations, with azetidinium as the cation which seems to play a role in driving such formation, implying that not just the size and the geometry of the molecule, affecting the rotational degrees of freedom, could play a role in perovskite formation
Summary
Organic/inorganic lead halide perovskites (LHPs), using earthabundant elements, have shown tremendous potential in achieving lab-scale efficiencies of solar cells approaching that of the crystalline silicon solar cells. The current high-performing LHPs are composed of methylammonium (MA), formamidinium (FA), and caesium (Cs) as the A-site cations in ABX3, which form a 3D structure. The current high-performing LHPs are composed of methylammonium (MA), formamidinium (FA), and caesium (Cs) as the A-site cations in ABX3, which form a 3D structure. This dimensionality, i.e., 3D, 2D, or 1D, estimated in terms of the Goldschmidt tolerance factor, is dependent on the size of the cation with all others remaining the same. Given the ideal size of Az to form a 3D perovskite with lead halides, research into utilizing this molecule as the cation in LHPs has been, surprisingly, very limited In this regard, we explore the utilization of Az in the synthesis of perovskite colloidal nanocrystals (NCs). Electronic transport is observed in the form of charge transfer to phenyl-C61-butyric acid methyl ester (PCBM) characterized using light-induced electron paramagnetic resonance (LEPR) spectroscopy
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