fabrication-fully-solution-processed-inorganic-nanocrystal

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

localized-bathless-metal-composite-plating-via-electrostamping

Localized Bathless Metal-Composite Plating via Electrostamping

Composite plating with particles embedded into the metal matrix can enhance the properties of the metal coating to make it more or less conductive, hard, ...

St. Mary's College of Maryland

Layered K(4)Nb(6)O(17) is a known UV-light-driven photocatalyst for overall water splitting, with a band gap of 3.5 eV. Following ion exchange and exfoliation with tetrabutylammonium hydroxide, the layered material separates into nanosheets that coil into 1.0±0.5 μm long and 10±5 nm wide nanoscrolls to reduce their surface energy. Pt and IrO(x) (x=1.5-2) nanoparticles were photochemically deposited onto the surface of the nanoscrolls to produce two- and three-component photocatalysts. Under UV irradiation, the nanostructures produced H(2) from pure water and aqueous methanol, with turnover numbers ranging from 2.3 and 18.5 over a 5 h period. The activity of the catalysts for H(2) evolution can be directly correlated with the varying overpotentials for water reduction (210-325 mV). From water, no oxygen is evolved. Instead, the formation of surface-bound peroxides in a 1:1 stoichiometry with H(2) is observed. Slow photochemical oxygen evolution can be achieved with the sacrificial electron acceptor AgNO(3), and under an electrochemical bias. The electrochemical water oxidation overpotentials are ca. 600 mV across the series of scrolls. From the photo onset potential the conduction band edge for the unmodified scrolls is estimated as -0.75 V at pH 7. Deposition of a co-catalyst is found to depress this value by 58 mV (IrO(x)), 148 mV (Pt/IrO(x)), and 242 mV (Pt). However, because water oxidation remains rate-limiting, this does not affect the overall performance of the catalysts.

Improved niobate nanoscroll photocatalysts for partial water splitting.

Rutile IrO(2) is known as being among the best electrocatalysts for water oxidation. Here we report on the unexpected photocatalytic water oxidation activity of 1.98 nm ± 0.11 nm succinic acid-stabilized IrO(2) nanocrystals. From aqueous persulfate and silver nitrate solution the nonsensitized particles evolve oxygen with initial rates up to 0.96 μmol min(-1), and with a quantum efficiency of at least 0.19% (measured at 530 nm). The catalytic process is driven by visible excitations from the Ir-d(t(2g)) to the Ir-d(e(g)) band (1.5-2.75 eV) and by ultraviolet excitations from the O-p band to the Ir-d(e(g)) (>3.0 eV) band. The formation of the photogenerated charge carriers can be directly observed with surface photovoltage spectroscopy. The results shed new light on the role of IrO(2) in dye- and semiconductor-sensitized water splitting systems.

Photocatalytic water oxidation with nonsensitized IrO2 nanocrystals under visible and UV light.

The photocatalytic hydrogen production of CdSe nanocrystals (1.75-4.81 nm) in the presence of aqueous sodium sulphite depends exponentially on the bandgap of the particles, confirming that the material's activity is controlled by the degree of quantum confinement.

Quantum confinement controlled photocatalytic water splitting by suspended CdSe nanocrystals.

SrTiO(3) (STO) is a large band gap (3.2 eV) semiconductor that catalyzes the overall water splitting reaction under UV light irradiation in the presence of a NiO cocatalyst. As we show here, the reactivity persists in nanoscale particles of the material, although the process is less effective at the nanoscale. To reach these conclusions, Bulk STO, 30 ± 5 nm STO, and 6.5 ± 1 nm STO were synthesized by three different methods, their crystal structures verified with XRD and their morphology observed with HRTEM before and after NiO deposition. In connection with NiO, all samples split water into stoichiometric mixtures of H(2) and O(2), but the activity is decreasing from 28 μmol H(2) g(-1) h(-1) (bulk STO), to 19.4 μmol H(2) g(-1) h(-1) (30 nm STO), and 3.0 μmol H(2) g(-1) h(-1) (6.5 nm STO). The reasons for this decrease are an increase of the water oxidation overpotential for the smaller particles and reduced light absorption due to a quantum size effect. Overall, these findings establish the first nanoscale titanate photocatalyst for overall water splitting.

Nanoscale strontium titanate photocatalysts for overall water splitting.

Soluble inorganic nanocrystals offer a potential route to the fabrication of all-inorganic devices using solution deposition techniques. Spray processing offers several advantages over the more common spin- and dip-coating procedures, including reduced material loss during fabrication, higher sample throughput, and deposition over a larger area. The primary difference observed, however, is an overall increase in the film roughness. In an attempt to quantify the impact of this morphology change on the devices, we compare the overall performance of spray-deposited versus spin-coated CdTe-based Schottky junction solar cells and model their dark current-voltage characteristics. Spray deposition of the active layer results in a power conversion efficiency of 2.3 ± 0.3% with a fill factor of 45.7 ± 3.4%, Voc of 0.39 ± 0.06 V, and Jsc of 13.3 ± 3.0 mA/cm(2) under one sun illumination.

Inorganic photovoltaic devices fabricated using nanocrystal spray deposition.

Solution-synthesized inorganic cadmium telluride nanocrystals (∼4 nm; 1.45 eV band gap) are attractive elements for the fabrication of thin-film-based low-cost photovoltaic (PV) devices. Their encapsulating organic ligand shell enables them to be easily dissolved in organic solvents, and the resulting solutions can be spray-cast onto indium-tin oxide (ITO)-coated glass under ambient conditions to produce photoactive thin films of CdTe. Following annealing at 380 °C in the presence of CdCl2(s) and evaporation of metal electrode contacts (glass/ITO/CdTe/Ca/Al), Schottky-junction PV devices were tested under simulated 1 sun conditions. An improved PV performance was found to be directly tied to control over the film morphology obtained by the adjustment of spray parameters such as the solution concentration, delivery pressure, substrate distance, and surface temperature. Higher spray pressures produced thinner layers (<60 nm) with lower surface roughness (<200 nm), leading to devices with improved open-circuit voltages (Voc) due to decreased surface roughness and higher short-circuit current (Jsc) as a result of enhanced annealing conditions. After process optimization, spray-cast Schottky devices rivaled those prepared by conventional spin-coating, showing Jsc = 14.6 ± 2.7 mA cm(-2), Voc = 428 ± 11 mV, FF = 42.8 ± 1.4%, and Eff. = 2.7 ± 0.5% under 1 sun illumination. This optimized condition of CdTe spray deposition was then applied to heterojunction devices (ITO/CdTe/ZnO/Al) to reach 3.0% efficiency after light soaking under forward bias. The film thickness, surface morphology, and light absorption were examined with scanning electron microscopy, optical profilometry, and UV/vis spectroscopy.

Impact of nanocrystal spray deposition on inorganic solar cells.

The effects of solution (sol) processed contacts of indium tin oxide (ITO-sol) and gold (Au-sol) on solar cells are tested. When combined with solution processed active layers of CdTe/CdSe, all-inorganic fully solution processed solar cells are produced on non-conductive glass substrates. Under AM 1.5G illumination, open circuit voltages (Voc), short circuit currents (Jsc) and efficiencies (η) of solar cells processed with evaporated Au and commercial ITO were found to be (Voc = 0.56 ± 0.04 V, Jsc = 17.2 ± 2.2 mA cm(-2), η = 3.8 ± 0.4%), with Au-sol replacement (Voc = 0.54 ± 0.03 V, Jsc = 12.6 ± 1.0 mA cm(-2), η = 2.0 ± 0.1%), with ITO-sol (Voc = 0.38 ± 0.04 V, Jsc = 12.3 ± 0.8 mA cm(-2), η = 1.3 ± 0.2%), and with each layer solution processed (Voc = 0.49 ± 0.01 V, Jsc = 10.0 ± 1.5 mA cm(-2), η = 1.5 ± 0.2%) with the champion fully-solution processed all-inorganic device showing η = 1.7%. Layers and devices were characterized with UV/Vis spectroscopy, optical profilometry, XRD, XPS and SEM. The results indicate that the reduced performance of the all-solution devices results primarily from increased roughness of the Au film and decreased conductivity of the ITO layer.

ArticleTotal : 2	Year
Publication title Cited by 4	2016
Publication title Cited by 1	2020

Article	Year
Improved niobate nanoscroll photocatalysts for partial water splitting. ChemSusChem\| PubMed ID: 21246751	2011
Photocatalytic water oxidation with nonsensitized IrO2 nanocrystals under visible and UV light. Journal of the American Chemical Society\| PubMed ID: 21524069	2011
Quantum confinement controlled photocatalytic water splitting by suspended CdSe nanocrystals. Chemical communications (Cambridge, England)\| PubMed ID: 22083249	2012
Nanoscale strontium titanate photocatalysts for overall water splitting. ACS nano\| PubMed ID: 22816530	2012
Inorganic photovoltaic devices fabricated using nanocrystal spray deposition. ACS applied materials & interfaces\| PubMed ID: 24007356	2013
Impact of nanocrystal spray deposition on inorganic solar cells. ACS applied materials & interfaces\| PubMed ID: 24755091	2014
Fully solution processed all inorganic nanocrystal solar cells. Physical chemistry chemical physics : PCCP\| PubMed ID: 24983645	2014

Troy K. Townsend

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