Deposition Mechanism of Aluminum Oxide on Quantum Dot Films at Atmospheric Pressure and Room Temperature

Abstract

Stability of quantum dot (QD) films is an issue of concern for applications in devices such as solar cells, LEDs, and transistors. This paper analyzes and optimizes the passivation of such QD films using gas-phase deposition, resulting in enhanced stability. Crucially, we deposited alumina at economically attractive conditions, room temperature and atmospheric pressure, on (1,2-ethanediamine) capped PbSe QD films using an approach based on atomic layer deposition (ALD), with trimethylaluminum (TMA) and water as precursors. We performed coating experiments from 1 to 25 cycles on the QD films, finding that alumina formed from the first exposure of TMA. X-ray photoelectron spectroscopy points to the presence of oxygen-rich compounds on the bare QD films, most likely from entrapped solvent molecules during the assembly of the QD films. These oxygenated compounds and the amine groups of the organic ligands react with TMA in the first cycle, resulting in a fast growth of alumina. Using 10 cycles resulted in a QD film that was optically stable for at least 27 days. Depositing alumina at ambient conditions is preferred, since the production of the QD films is also carried out at room temperature and atmospheric pressure, allowing combination of both processes in a single go.

CsPbBr3 QD/AlOx Inorganic Nanocomposites with Exceptional Stability in Water, Light, and Heat

“…[17,38] An alternative explanation for this quenching effect at higher irradiation densities is the photoinduced desorption of surface ligands and the subsequent formation of carrier trapping defects,a sp reviously reported for chalcogenide QD films. [2,25,[41][42][43][44][45][46] On the contrary,n oa dditional XRD peaks were observed for the nanocomposites.H owever,adecrease of 20 %i nt he full width at half maximum (FWHM) of the (200) peak suggests that necking of those QDs not fully covered by the alumina might occur (Figures S20 and S21). Upon annealing, the pristine QD film shows clear sintering and additional peaks that are consistent with the presence of the thermodynamically stable orthorhombic phase (Figures S20 and S21).…”

“…[11] Silica has also been used as am atrix to protect inorganic perovskite QDs. [16][17][18][20][21][22][23][24][25] However,n oa pplication to perovskite QDs has been reported thus far.T he high sensitivity to moisture,t emperature,a nd light of this class of QDs makes the development of an optimal ALD process not trivial. Thebottom line is that while for organic-inorganic perovskites,d ifferent stabilizing approaches have been successfully implemented, which are based mostly on polymers,noreliable approach exists for inorganic perovskite QDs.…”

“…Thus the two signals,w hich overlap in EDX, could be mapped, confirming the presence of not only ap ure Alcontaining overcoat, but also of the AlO x deposited at the bottom substrate layer. [25] Thus it is suggested that in the initial stage of nucleation, the TMA reacts with the partially oxidized QD surface.U pon saturation of the oxidized surface sites,t he TMA molecules intercalate at the hydrophilic ligand/QD interface as recently proposed by Li and co-workers. TheXPS data also gave some insight into the stoichiometry of the amorphous alumina matrix.…”

Suppressing the Photocatalytic Activity of TiO2 Nanoparticles by Extremely Thin Al2O3 Films Grown by Gas-Phase Deposition at Ambient Conditions

“…The high reactivity of TMA facilitates the deposition of Al 2 O 3 in a broad range of temperature on various types of substrates and materials with any geometries, including flat surfaces [21], high-aspect-ratio structures [41,42,43], porous media [44,45,46,47], nanoparticles [29,32,34,40], fibers [48], carbon nanotubes [49,50], graphene [51,52,53], polymers [54], and biomaterials [55]. The reaction mechanism in ALD of Al 2 O 3 using TMA and H 2 O has been intensively investigated in the past decades, both theoretically and experimentally [21,56,57,58,59,60,61,62,63,64,65,66,67].…”

Atomic Layer Deposition of ZnO on InP Quantum Dot Films for Charge Separation, Stabilization, and Solar Cell Formation

“…Previous studies on ALD coating of QD films have looked at Al 2 O 3 or ZnO growth on PbS(e) and CdSe QDs, and have mostly focused on enhancing their (air) stability, rather than on making a functional coating that results in charge separation. Here we grow a functional electron transport layer of either TiO 2 or ZnO via ALD on Pb‐ and Cd‐free InP QDs.…”