MIST DEPOSITION, PATTERNING AND APPLICATIONS OF CADMIUM SELENIDE NANOCRYSTALLINE QUANTUM DOT FILMS
Open Access
- Author:
- Sabeeh, Ala Hamza
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 26, 2019
- Committee Members:
- Jerzy Ruzyllo, Dissertation Advisor/Co-Advisor
Jerzy Ruzyllo, Committee Chair/Co-Chair
Osama O Awadelkarim, Committee Member
Noel Christopher Giebink, Committee Member
Joshua Alexander Robinson, Outside Member - Keywords:
- Nanocrystalline Quantum Dots
Mist Deposition
Patterning
Lift-off Process
Downshifting
Silicon Solar Cell
micro-patterns
thin film - Abstract:
- Nanocrystalline quantum dots (NQD) have gained attention because of their unique properties, including a tunable energy gap, broad emission spectra, and high photoluminescence, which have made them of interest in various photoelectronic device applications. A challenge in the NQD-based device fabrication process is to create ultrathin films featuring well-defined micropatterns, and to integrate them with functional devices. This study is concerned with a technology using CdSe NQD films in the manufacture of functional devices. It uses the mist deposition technique to create monolayer and multilayer films of CdSe NQD. Various patterning methods accompanied with mist deposition to create well-defined NQD-micropatterned films are considered in this thesis. Also, the effectiveness of mist deposited CdSe NQD films in fabricating functional devices is illustrated.The first phase of the investigation concerns NQD film formation by means of mist deposition toward full control over film thickness. The mist deposition method proves its effectiveness, as compared with available deposition technique, in controlling NQD film thickness varying from 10 nm up to 100 nm, with uniform and low roughness surface.The second phase of the investigation examines how to create NQD patterned films by different methods, including mechanical mask patterning, self-assembly monolayer patterning, and lift-off patterning. Mechanical mask patterning is explored in terms of the effects of mask materials and electric field on the NQD patterned films formation. The results illustrate that masks made of an insulating material allow uniform film deposition,while electrically conductive mask material prevent deposition. The resolution of the patterned NQD films are varied from several millimeters down to 100 μm. The self-assembly monolayer patterning (a bottom-up process) is performed by means of surface functionalization and explored in terms of chemical composition, rapid optical surface treatment (ROST), and ultraviolet (UV) exposure of the surface to study its effect on NQD film selective deposition. The results obtained demonstrate a successful area selective deposition of patterned NQD films using both ROST and UV surface treatments on different substrates, with the resolution of about 100 μm. The lift-off patterning method is implemented in gas-phase (oxygen plasma exposure) and liquid-phase (acetone immersion) to produce high resolution NQD patterned films. The results illustrate NQD’s well-defined patterns with resolution of about 1 μm, regardless of the lift-off ambient used. The obtained NQD patterned films were characterized further by means of fluorescence characterization and image processing tool to study the light intensity of NQD patterned surface. The results obtained indicate the effectiveness of the liquid-phase lift-off in patterning NQD films with uniform surface intensity as compared with the gas-phase lift-off. The effects of lift-off parameters such as photoresist thickness, solvent composition, and substrate surface are investigated in terms of their effect on NQD film coverage. The results indicate that at least 3:1 ratio of photoresist thickness to NQD film thickness is needed to assure adequate coverage of NQD patterned films after lift-off. The third phase of the investigation explores the effectiveness of mist-deposited downshifting CdSe NQD films both continuous and patterned on the performance of single-crystal silicon solar cells. Different thicknesses of NQD films are explored in an attempt to improve cell efficiency in the UV range (below 400 nm) of the solar spectrum. The results obtained indicate that the maximum UV absorption is observed with a 50 nm thick NQD film, as reflected by an increase of 45% in the average UV external quantum efficiency (EQE) as compared with solar cell without NQD film. The patterned NQD films show improved performance in the visible range as compared with continuous NQD films, without compromising cell performance in the UV range of the solar spectrum. Also, an increase in power conversion efficiency by 12.5% is observed using patterned CdSe NQD films on the solar cell surface. A conclusion from this investigation is that the mist deposition of NQD film can effectively supplement other deposition methods, such as spin-on, in the film thickness regime below 100 nm. It is also demonstrated that the mist-deposited NQD films are compatible with a range of patterning techniques.