11 research outputs found
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Development of solution processed, flexible, CuInSeâ‚‚ nanocrystal solar cells
Clean sources of energy, especially photovoltaics (PVs), are urgently needed to cope with global energy shortage and environmental pollution. For PVs to play a significant role in energy production, the current prices must be brought down. Thin film PVs made using layered Mo or Au/CuInGaSeâ‚‚(CIGS)/CdS/ZnO/ITO have already shown high efficiencies. Traditionally, most layers in CIGS solar cells are deposited using high-cost techniques requiring high temperatures and ultra-low pressures. By replacing the traditionally processed CIGS with a nanocrystal layer that can be deposited at mild processing conditions, the fabrication cost can be reduced. In this study, a high yielding synthesis method for CuInSeâ‚‚ nanocrystals has been developed which gives the best efficiency (3.1%), so far, for low-temperature processed CuInSeâ‚‚ nanocrystal PVs. An important challenge that nanocrystal solar cells currently face is low device efficiency, resulting in higher operating cost. CuInSeâ‚‚ nanocrystals can remain suspended in solution because of the long chain organic ligands attached to the surface. However, these ligands hinder charge transfer between nanocrystals causing low device efficiency. These ligands have been successfully replaced with smaller sulfide ions thereby improving the best efficiency of low-temperature processed CuInSeâ‚‚ nanocrystal solar cells from 3.1 % to 3.5%. Another approach to reducing the cost of CuInSeâ‚‚ PVs is by replacing the glass support medium with cheaper alternatives like paper. Flexible CuInSeâ‚‚ nanocrystal solar cells are successfully fabricated on paper with efficiencies reaching up to 2.25%. This is the first time a nanocrystal solar cell has been fabricated on paper. There is no significant loss in PV device performance after more than 100 flexes to 5 mm radius, and the devices continue to perform when folded into a crease. Apart from the absorber layer, the replacement of other high-temperature and vacuum processed device layers with ambient solution-processed layers lowers the manufacturing cost. This has been achieved by spin coating suitable nanomaterials as device layers. Lastly, for commercialization of CuInSeâ‚‚ nanocrystal solar cells, multiple devices need to be connected to achieve the desired current and voltage. A fabrication process has been developed for building multiple nanocrystal PVs on a single substrate using 3D printed masksChemical Engineerin
Uniform selenization of crack-free films of Cu(In,Ga)Se2 nanocrystals
Crack-free films of Cu(In,Ga)Se2 (CIGS) nanocrystals were deposited with uniform thickness (>1 ÎĽm) on Mo-coated glass substrates using an ink-based, automated ultrasonic spray process, then selenized and incorporated into photovoltaic devices (PVs). The device performance depended strongly on the homogeneity of the selenized films. Cracks in the spray-deposited films resulted in uneven selenization rates and sintering by creating paths for rapid, uncontrollable selenium (Se) vapor penetration. To make crack-free films, the nanocrystals had to be completely coated with capping ligands in the ink. The selenization rate of crack-free films then depended on the thickness of the nanocrystal layer, the temperature, and duration of Se vapor exposure. Either inadequate or excessive Se exposure leads to poor device performance, generating films that were either partially sintered or exhibited significant accumulation of carbon and selenium. The deposition of uniform nanocrystal films is expected to be important for a variety of electronic and optoelectronic device applications.Fil: Harvey, Taylor B.. Texas A&M University; Estados UnidosFil: BonafĂ©, Franco PaĂşl. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; ArgentinaFil: Updegrave, Ty. University of Texas at Austin; Estados UnidosFil: Voggu, Vikas Reddy. University of Texas at Austin; Estados UnidosFil: Thomas, Cherrelle. University of Texas at Austin; Estados UnidosFil: Kamarajugadda, Sirish C.. University of Texas at Austin; Estados UnidosFil: Stolle, C. Jackson. University of Texas at Austin; Estados UnidosFil: Pernik, Douglas. University of Texas at Austin; Estados UnidosFil: Du, Jiang. University of Texas at Austin; Estados UnidosFil: Korgel, Brian A.. University of Texas at Austin; Estados Unido
Orientationally ordered silicon nanocrystal cuboctahedra in superlattices
This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlUniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices
Bubble Assemblies of Nanocrystals: Superlattices without a Substrate
A method was developed
to create free-standing nanocrystal films
in the form of solidified bubbles. Bubbles of octadecanethiol-capped
gold nanocrystals were studied by in situ grazing incidence small-angle
X-ray scattering (GISAXS) to determine how the absence of an underlying
substrate influences a disorder–order transition of a nanocrystal
superlattice. We find that the presence of the substrate does not
significantly change the nature of the disorder–order transition
but does lead to reduced interparticle separation and reduced thermal
expansion. Bubble assemblies of silicon and copper selenide nanocrystals
are also demonstrated
Orientationally ordered silicon nanocrystal cuboctahedra in superlattices
This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlUniform silicon nanocrystals were synthesized with cuboctahedral shape and passivated with 1-dodecene capping ligands. Transmission electron microscopy, electron diffraction, and grazing incidence wide-angle and small-angle X-ray scattering show that these soft cuboctahedra assemble into face-centered cubic superlattices with orientational order. The preferred nanocrystal orientation was found to depend on the orientation of the superlattices on the substrate, indicating that the interactions with the substrate and assembly kinetics can influence the orientation of faceted nanocrystals in superlattices
Cooling Dodecanethiol-Capped 2 nm Diameter Gold Nanocrystal Superlattices below Room Temperature Induces a Reversible Order–Disorder Structure Transition
We recently observed
that a disordered assembly of octadecanethiol-capped
gold (Au) nanocrystals can order when heated from room temperature
to 60 °C [Yu, Y.; Jain, A.; Guillaussier, A.; Voggu, V. R.; Truskett,
T. M.; Smilgies, D.-M.; Korgel, B. A. <i>Faraday Discuss.</i> <b>2015</b>, <i>181</i>, 181–192]. This “inverse
melting” structural transition was reversible and occurred
near the melting-solidification temperature of the capping ligands.
To determine the generality of this phenomenon, we studied by in situ
grazing incidence small-angle X-ray scattering (GISAXS) the structure
of assemblies of Au nanocrystals with shorter C<sub>12</sub> and C<sub>5</sub> alkanethiol capping ligands that form ordered superlattices
at room temperature and have a ligand melting-solidification temperature
below room temperature. Superlattices of dodecanethiol-capped Au nanocrystals
disorder when cooled below 260 K, which is the melting-solidification
temperature for dodecanethiol. Au nanocrystals capped with even shorter
pentanethiol ligands that have a melting transition below 100 K (the
lowest experimentally accessible temperature) do not undergo the disorder
transition
Flexible CuInSe<sub>2</sub> Nanocrystal Solar Cells on Paper
Solar
cells on paper have the potential to be inexpensive and portable
due to several unique features of the substrate: paper is cheap, flexible,
lightweight, biodegradable, and manufactured by roll-to-roll processing.
Here, we report the first nanocrystal photovoltaic devices (PVs) made
on paper. Using spray-deposited CuInSe<sub>2</sub> nanocrystals as
the absorber material on substrates composed of bacterial cellulose
nanofibers synthesized by the microorganism <i>Gluconacetobacter
hansenii</i>, these devices demonstrate exceptional electrical
and mechanical integrity. There is no significant loss in PV device
performance after more than 100 flexes to 5 mm radius, and the devices
continue to perform when folded into a crease. The practical use of
these paper PVs is demonstrated with a prototype device powering liquid
crystal displays (LCDs) mounted to various kinds of surfaces
Silicon Nanocrystal Superlattice Nucleation and Growth
Colloidal
dodecene-passivated silicon (Si) nanocrystals were dispersed
in hexane or chloroform and deposited onto substrates as face-centered
cubic superlattices by slowly evaporating the solvent. The uniformity
of the nanocrystals enables extended order; however, the solvent and
the evaporation protocol significantly influence the self-assembly
process, determining the morphology of the films, the extent of order,
and the superlattice orientation on the substrate. Chloroform yielded
superlattices with step-flow growth morphologies and (111)<sub>SL</sub>, (100)<sub>SL</sub>, and (110)<sub>SL</sub> orientations. Hexane
led to mostly island morphologies when evaporated at room temperature
with exclusively (111)<sub>SL</sub> orientations. Higher evaporation
temperatures led to more extensive step-flow deposition. A model for
the surface diffusion of nanocrystals adsorbed on the superlattice
surface is developed
Orientationally Ordered Silicon Nanocrystal Cuboctahedra in Superlattices
Uniform silicon nanocrystals
were synthesized with cuboctahedral shape and passivated with 1-dodecene
capping ligands. Transmission electron microscopy, electron diffraction,
and grazing incidence wide-angle and small-angle X-ray scattering
show that these soft cuboctahedra assemble into face-centered cubic
superlattices with orientational order. The preferred nanocrystal
orientation was found to depend on the orientation of the superlattices
on the substrate, indicating that the interactions with the substrate
and assembly kinetics can influence the orientation of faceted nanocrystals
in superlattices