Transparent Conductive Oxide Nanocrystals Coated with Insulators by Atomic Layer Deposition

Abstract

Thin films comprised of transparent conductive oxide (TCO) nanocrystals are attractive for a number of optoelectronic applications. However, it is often observed that the conductivity of such films is very low when they are in contact with air. It has recently been demonstrated, somewhat surprisingly, that filling in initially insulating films comprised of TCO nanocrystals with another insulator by atomic layer deposition (ALD) dramatically increases the conductivity by many orders of magnitude. This work aims to elucidate the mechanism by which the ALD coating increases conductivity. We examined the effect of removing two adsorbed oxygen species (physisorbed molecular water and chemisorbed hydroxide) on sheet resistance and compared this result to the results with thin films comprised of ZnO nanocrystals coated with Al2O3 and also HfO2 by ALD. Although both insulating infills decrease the sheet resistance and increase the stability of the films, there is a stark discrepancy between the two. From the in situ measurements, it was found that coating with Al2O3 removes both physisorbed water and chemisorbed hydroxide, resulting in a net reduction of the ZnO nanocrystals. Coating with HfO2 removes only physisorbed water, which was confirmed by Fourier transform infrared spectroscopy. A similar phenomenon was observed when thin films comprised of Sn-doped In2O3 nanocrystals were coated, suggesting Al2O3 can be used to reduce and stabilize metal oxide nanocrystals in general.

Impacts of surface depletion on the plasmonic properties of doped semiconductor nanocrystals

“…Surface depletion and associated band bending in NCs strongly impacts their potential applications in sensing, electro-optics, and transparent conductors. Surface depletion could also strongly impact carrier transport through NC-based transparent conductors by imposing a potential barrier at NC-NC interface53 .Strong dependence of LSPR modulation, sensitivity to the surrounding, and near-field enhancement on size and doping concentration of the NCs -all due to surface depletionhighlights the importance of rational choice of the NCs for a given application. For smart window applications12,15 , where the maximum LSPR frequency and intensity modulation is desirable, low doped and small sized NCs are preferable.…”

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

“…[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.…”

“…[16][17][18][19] Previous works have shown that metal oxide matrices (Al 2 O 3 and ZnO) improve the oxidative and photothermal stability of other QDs (PbSe,P bS,C dSe, CdSe@ZnS,a nd CdTe). [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. Fore xample,l ow temperature and short water pulses are mandatory to avoid QD degradation.…”

Nanocrystal‐based inorganic nanocomposites: A new paradigm for plasma‐produced optoelectronic thin films

“…The authors suggested that the ALD treatment removed electron trap states at the nanocrystal surface associated with hydroxyl (OH) groups, which reacted with the trimethylaluminum precursor to form aluminum–oxygen bonds. Other studies suggested that the removal of physisorbed water [ 41 ] and surface bonded carboxylate groups [ 42 ] was also important in decreasing the density of electron trap states.…”