Abstract

Self-assembled TiO2 foam-like films, were grown by the water based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). The morphology of the ∼1 µm thick films consists of a tangled ropy structure with individual strands of ∼ 200 nm diameter and open pores of 0.1 to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprising CH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers, all deposited by SPEED. Lateral film resistivity is in the range 20 - 200 kΩ-cm, increasing with growth temperature, while sheet resistance is in the range 2 − 20 × 108 Ω/Sq. Xray diffraction confirms presence of TiO2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy shows high transmission below the expected 3.2 eV TiO2 bandgap. Transmittance increases with growth temperature. This is a Ropy TiO2 thin film. We also prepared a Smooth TiO2 thin film. Self-assembled TiO2 film deposited by aqueous-spray deposition was investigated to evaluate morphology, crystalline phase, and infrared optical constants. The Anatase nano-crystalline film had ∼10 nm characteristic surface roughness sparsely punctuated by defects of not more than 200 nm amplitude. The film is highly transparent throughout the visible to wavelengths of 12 µm. The indirect band gap was determined to be 3.2 eV. Important for long-wave infrared applications is that dispersion in this region is weak compared with the more commonly used dielectic SiO2 for planar structures. The low-cost, large-area, atmosphericpressure, chemical spray deposition method allows conformal fabrication on flexible substrates for long-wave infrared photonics. For comparison TiO2 films deposited by electron-beam evaporation were evaluated to determine morphology, crystalline phase, and optical transparency. The evaporated TiO2 film was amorphous but crystallized into Anatase phase after annealing. Such film is attractive as electron conductor of unprecedented thinness and flexibility for proposed perovskite solar cell comprising CH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers. The spray deposition method would allow conformal solar cell fabrication on flexible substrates for wearable power generation. Band gap of Evaporated TiO2 film is 4.0 eV. We prepared BaTiO3 thin film to know infrared pyroelectric response. Self-assembled nano-crystalline BaTiO3 films on stainless steel foil substrates, were grown by the water based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). SPEED is an aqueous process that deposits self-assembled nano-crystalline inorganic thin films over large areas, without a vacuum, providing a scalable and manufacturing friendly process to fabricate durable films. The morphology of the ∼1µm thick films comprises single crystals of micron dimensions imbedded in a matrix of nanocrystals. XRD confirms presence of BaTiO3 crystals of hexagonal phase for samples annealed at 500◦C. Subsequent annealing at 600◦C transforms the film to the cubic phase. Potential applications include dielectric layers, capacitors, waveguides, ferroelectric RAM, pyroelectric infrared detectors, and phosphors. Characterization of infrared pyroelectric response at 10µm wavelength shows an initially good sensitivity that reversibly decays over a period of days due to water vapor absorption. A short-lived photo-response due to poling of the hydrated sample is also observed. We studied BaTiO3 to know hysteresis loop. Pyroelectric photoresponse of aqueous spray deposited thin films containing BaTiO3 nano-crystals is reported. X-ray diffraction data indicate the presence of hexagonal BaTiO3 nano-crystals with ∼20 nm crystalline domains in a matrix of some as yet unidentified nano-crystalline material. When the film is annealed at 600◦C, the X-ray pattern changes significantly and indicates a conversion to one of the non-hexagonal phases of BaTiO3 as well as a complete change in the matrix. With suitable amplifier, the measured photoresponse was 40V/W. Ferroelectric hysteresis on a film with significant presence of hexagonal BaTiO3 shows saturated polarization which is about 5-times smaller than for the bulk tetragonal phase.

Notes

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Graduation Date

2017

Semester

Summer

Advisor

Peale, Robert

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Electrical Engineering and Computer Engineering

Degree Program

Electrical Engineering

Format

application/pdf

Identifier

CFE0006710

URL

http://purl.fcla.edu/fcla/etd/CFE0006710

Language

English

Release Date

August 2017

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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