The micropatterning of layers of colloidal quantum dots with inorganic ligands using selective wet etching

Abstract

The micropatterning of layers of colloidal quantum dots (QDs) stabilized by inorganic ligands is demonstrated using PbS core and CdSe/CdS core/shell QDs. A layer-by-layer approach is used to assemble the QD films, where each cycle involves the deposition of a QD layer by dip-coating, and the replacement of the native organic ligands by inorganic moieties, such as OH(-) and S(2-), followed by a thorough cleaning of the resulting film. This results in a smooth and crack-free QD film on which a photoresist can be spun. The micropatterns are defined by a positive photoresist, followed by the removal of uncovered QDs by selective wet etching with an HCl/H3PO4 mixture. The resulting patterns can have submicron feature dimensions, limited by the resolution of the lithographic process, and can be formed on planar and 3D substrates. It is shown that the photolithography and wet etching steps have little effect on the photoluminescence quantum yield of CdSe/CdS QDs. Compared with the unpatterned CdSe/CdS QD film, only a 10% degradation in the quantum yield is observed. These results demonstrate the feasibility of the proposed micropatterning method to implement the large-scale device integration of colloidal quantum dots.

Air-stable short-wave infrared PbS colloidal quantum dot photoconductors passivated with Al2O3 atomic layer deposition

“…Homogenous and crack-free QD films are obtained by a layer-by-layer (LBL) approach, where each cycle involves a QD layer deposition through dip coating, followed by a replacement of the native organic ligand by a metal-free inorganic ligand, such as OH À and S 2À Ref. 10. Afterwards, a thorough cleaning procedure is used to remove impurities.…”

“…For surface illuminated detectors, the QD films are formed on prefabricated interdigitated electrodes, where selective wet etching is used to pattern the QD film. 10 The resulting photodetectors are then passivated with an aluminum oxide coating through ALD. [11][12][13][14] Long term air-stable PbS colloidal QD photodetectors with a 2.4 lm cut-off wavelength are obtained this way.…”

“…After the synthesis, the OlAm ligands were replaced by oleic acid (OlAc) to obtain a ligand shell that withstands successive purification cycles. 10,15 The ligand exchange was realized by adding OlAc to a PbS QD in toluene suspension with a volume ratio of 1.5:10 (OlAc: toluene). Afterwards, the suspension was purified using methanol (MeOH) and toluene as the non-solvent and the solvent, respectively.…”

“…The photodetectors were fabricated by 15 times LBL deposition. Afterwards a selective wet-etching approach was used to realize micropatterned QD films on prefabricated electrodes, 10 resulting in PbS QD films of 130 lm by 104 lm. Then atomic layer deposition of Al 2 O 3 was used to passivate the devices.…”

Active Liquid Crystal Tuning of Metallic Nanoantenna Enhanced Light Emission from Colloidal Quantum Dots

“…Colloidal QDs constitute ideal emitters for this purpose as they offer sharp and tunable emission properties, even at ambient or higher temperatures, in combination with a versatile processability. 43 The active tuning is achieved by changing the temperature of the sample. Above a critical temperature T c , the orientation of the LC becomes randomized, and the effective refractive index switches from birefringent to isotropic.…”