Interplay between Perovskite Magic-Sized Clusters and Amino Lead Halide Molecular Clusters

Abstract

Recent progress has been made on the synthesis and characterization of metal halide perovskite magic-sized clusters (PMSCs) with ABX3 composition (A=CH3NH3+ or Cs+, B=Pb2+, and X=Cl−, Br-, or I-). However, their mechanism of growth and structure is still not well understood. In our effort to understand their structure and growth, we discovered that a new species can be formed without the CH3NH3+ component, which we name as molecular clusters (MCs). Specifically, CH3NH3PbBr3 PMSCs, with a characteristic absorption peak at 424 nm, are synthesized using PbBr2 and CH3NH3Br as precursors and butylamine (BTYA) and valeric acid (VA) as ligands, while MCs, with an absorption peak at 402 nm, are synthesized using solely PbBr2 and BTYA, without CH3NH3Br. Interestingly, PMSCs are converted spontaneously overtime into MCs. An isosbestic point in their electronic absorption spectra indicates a direct interplay between the PMSCs and MCs. Therefore, we suggest that the MCs are precursors to the PMSCs. From spectroscopic and extended X-ray absorption fine structure (EXAFS) results, we propose some tentative structural models for the MCs. The discovery of the MCs is critical to understanding the growth of PMSCs as well as larger perovskite quantum dots (PQDs) or nanocrystals (PNCs).

Varying the Concentration of Organic Acid and Amine Ligands Allows Tuning between Quantum Dots and Magic-Sized Clusters of CH3NH3PbBr3 Perovskite: Implications for Photonics and Energy Conversion

“…Based on the previous study from our group, this peak can be attributed to molecular clusters (MCs). 26,63 A similar trend is observed in the PL spectra. Initially, for 0.050 mM OcAm, there was one broad emission peak at 513 nm, which was attributed to PQDs.…”

“…With 6.25 mM OcAm, an additional absorption peak was observed at 396 nm. Based on the previous study from our group, this peak can be attributed to molecular clusters (MCs). , …”

Synthesis and Optical Properties of Mn2+-Doped Amino Lead Halide Molecular Clusters Assisted by Chloride Ion

“…For the undoped PbBr 2 –OcAm sample, the UV–vis absorption spectrum exhibits a strong and sharp electronic absorption band peak at 405 nm, whereas the PL spectrum has an emission band peak at 410 nm. We attributed these absorption and emission bands to MCs based on our previous work . The PLE spectra collected at 410 nm emission shows a peak near 400 nm that is close to the electronic absorption peak.…”

“…Recently, in our effort to understand the growth mechanism of PNCs and related magic sized clusters (MSCs), a new species named amino lead halide molecular clusters (MCs) was discovered . Compared with PNCs, MSCs and MCs are single sized and/or very narrow size distributed particles that are smaller and more uniform in size and shape.…”

“…Importantly, there is an equilibrium existing between MSCs and MCs. MSCs are converted spontaneously over time into MCs, and MCs can revert back to MSCs under the right experimental conditions . MCs can be viewed as important precursors in the formation of MSCs or PNCs. , Their unique characteristics, including small and supposedly single size as well as relatively strong photoluminescence (PL), make them intriguing for fundamental research , and potentially useful for photonics applications such as blue single photon emitters.…”