Simultaneous Ligand and Cation Exchange of Colloidal CdSe Nanoplatelets toward PbSe Nanoplatelets for Application in Photodetectors

Abstract

Cation exchange emerged as a versatile tool to obtain a variety of nanocrystals not yet available via a direct synthesis. Reduced reaction times and moderate temperatures make the method compatible with anisotropic nanoplatelets (NPLs). However, the subtle thermodynamic and kinetic factors governing the exchange require careful control over the reaction parameters to prevent unwanted restructuring. Here, we capitalize on the research success of CdSe NPLs by transforming them into PbSe NPLs suitable for optoelectronic applications. In a two-phase mixture of hexane/Nmethylformamide, the oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH 4 I and a cation exchange reaction to PbSe. Their morphology and crystal structure are well-preserved as evidenced by electron microscopy and powder X-ray diffraction. We demonstrate the successful ligand exchange and associated electronic coupling of individual NPLs by fabricating a simple photodetector via spray-coating on a commercial substrate. Its optoelectronic characterization reveals a fast light response at low operational voltages.

Nonblinking Colloidal Quantum Dots via Efficient Multiexciton Emission

“…Classified as solution-processed semiconductor nanocrystals with size- and shape-dependent luminescence emission, colloidal quantum dots (QDs) cover a spectral range from ultraviolet to near-infrared due to the quantum confinement effect. , To date, extensive attention has been paid to research on how to synthesize high-quality QDs with a near-unity photoluminescence quantum yield (PLQY) and color-pure emission, demonstrating their potential for applications in a variety of optoelectronic devices such as lasers, light-emitting diodes, , photodetectors, , liquid-crystal displays, and single-photon sources . Although stable luminescence emission plays an essential role in their widespread applications in these fields, most synthesized QDs are prone to blinking at the single-particle level, , which is especially significant at high excitation intensities.…”

Halometallates Bind as Z-Type Ligands on Wurtzite CdSe Nanoplatelets

“…Semiconductor nanocrystals are typically synthesized with ligands containing long alkyl chains, such as oleate and n -octylamine, which impede inter-nanocrystal electronic coupling and carrier transport in nanocrystal solids . Consequently, effort has been committed to replacing these native ligands with smaller, inorganic ligands. − These studies have included halometallate ligands of general formula MX n z– , with CdCl 3 – and PbI 3 – as some specific examples. − Kovalenko and co-workers demonstrated that halometallate ligation of semiconductor nanocrystals stabilized their dispersions in polar solvents and retained high nanocrystal photoluminescence efficiencies . Talapin and co-workers reported that CdCl 3 – ligands afforded high-concentration CdTe nanocrystal inks and also functioned as grain-growth promoters in sintered films, which were employed in high-efficiency solar cells .…”

Chemical Transformations of Colloidal Semiconductor Nanocrystals Advance Their Applications

“…A partial Cd 2+ -to-Pb 2+ cation exchange applied to CdSe tetrapods yielded heterostructured PbSe-tipped CdSe tetrapods with PL maxima tunable from 1000 nm to more than 2000 nm . A facile procedure recently developed by Galle et al combines ligand and cation exchanges on CdSe NPLs (Figure a) . In this process, oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH 4 I and a cation exchange reaction to PbSe in a two-phase mixture of hexane/MFA under mild conditions, preserving their morphology and crystal structure.…”

“…Tracing of the frequency-dependence and determination of the cutoff frequency of the device using a blue LED and a signal generator to modulate the light (f). Adapted with permission from ref . Copyright 2021 American Chemical Society.…”

“…64 A facile procedure recently developed by Galle et al combines ligand and cation exchanges on CdSe NPLs (Figure 7a). 65 In this process, oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH 4 I and a cation exchange reaction to PbSe in a two-phase mixture of hexane/MFA under mild conditions, preserving their morphology and crystal structure. The resulting PbSe NPLs after purification and dissolving in DFP were processed into thin films by spray-coating onto a commercial platinum electrode, forming a simple photodetector, whose structure and performance are presented in panels b and c−f of Figure 7, respectively.…”