Switching between Plasmonic and Fluorescent Copper Sulfide Nanocrystals

Abstract

Control over the doping density in copper sulfide nanocrystals is of great importance and determines its use in optoelectronic applications such as NIR optical switches and photovoltaic devices. Here, we demonstrate that we can reversibly control the hole carrier density (varying from >1022 cm–3 to intrinsic) in copper sulfide nanocrystals by electrochemical methods. We can control the type of charge injection, i.e., capacitive charging or ion intercalation, via the choice of the charge compensating cation (e.g., ammonium salts vs Li+). Further, the type of intercalating ion determines whether the charge injection is fully reversible (for Li+) or leads to permanent changes in doping density (for Cu+). Using fully reversible lithium intercalation allows us to switch between thin films of covellite CuS NCs (Eg = 2.0 eV, hole density 1022 cm–3, strong localized surface plasmon resonance) and low-chalcocite CuLiS NCs (Eg = 1.2 eV, intrinsic, no localized surface plasmon resonance), and back. Electrochemical Cu+ ion intercalation leads to a permanent phase transition to intrinsic low-chalcocite Cu2S nanocrystals that display air stable fluorescence, centered around 1050 nm (fwhm ∼145 meV, PLQY ca. 1.8%), which is the first observation of narrow near-infrared fluorescence for copper sulfide nanocrystals. The dynamic control over the hole doping density and fluorescence of copper sulfide nanocrystals presented in this work and the ability to switch between plasmonic and fluorescent semiconductor nanocrystals might lead to their successful implementation into photovoltaic devices, NIR optical switches and smart windows.

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

“…In the big family of Cu chalcogenide compounds, Cu vacancies commonly exist by ambient exposure, [34] which probably stems from its superionic nature [35] and thus weak Cu-S bonding. The deficiency of Cu ions, which serve as electron donor in semiconductor, leads to the self-doping of high density (up to 10 21 cm −3 ) holes in Cu 2−x S. [36] Consequently, in theory the conductivity of Cu 9 S 5 is high. The electrical transport property of the Cu 9 S 5 nanoflakes was measured using a back-gated FET configuration on a p-type silicon substrate that was covered by 300 nm thick SiO 2 as dielectric layer.…”

Ultrasmall aqueous starch-capped CuS quantum dots with tunable localized surface plasmon resonance and composition for the selective and sensitive detection of mercury(ii) ions

“…9 Stam et al reported that Cu + ions intercalation leads to permanent phase transition from CuS to Cu 2 S NCs, whereas Li + ions interaction leads to reversible transition between CuS and CuLiS structures. 18 Recently, Liu et al reported the reversible nanoscale interconversion from CuS to Cu 2 S nanocrystals (NCs) and vice versa. 14 It is well known that Hg 2+ ions have strong affinity towards sulfur ligands and sulfur anions (S 2À ) due to so-so interactions.…”

Electrochemical Fingerprint of CuS-Hexagonal Chemistry from (Bis(N-1,4-Phenyl-N-(4-Morpholinedithiocarbamato) Copper(II) Complexes) as Photon Absorber in Quantum-Dot/Dye-Sensitised Solar Cells

“…Copper monosulfide (CuS) has distinguished itself among metal sulfides owing to its different band gap and various morphologies. This makes CuS a hot-spot semiconductor material with great potential in the field of photocatalytic and photovoltaic applications [18][19][20][21][22][23][24][25][26]. Hexagonal covellite-CuS with a bandgap of ∼2 eV and a p-type-enhances absorber abilities to cover the entire solar spectrum [18,19].…”