Controlling SALD-Deposited ZTO Nanofilm Composition and Implications for their use as Perovskite Solar Cell Transport Layers

This thesis is concerned with the study of new nanofilm electron transport layers for use in perovskite solar cells, one of the thin film solar cell technologies in the research and very early commercial phases. Spatial atomic layer deposition (SALD) is a method of nanofilm growth that is particularly well-suited to metal oxide fabrication, yielding high-quality uniform films in less time and without the cumbersome vacuum requirements of conventional atomic layer deposition. An important attribute of a performant electron transport layer is the appropriate matching of its conduction and valence band energy levels to those of the perovskite in contact with it, to favour electron extraction into the transport layer and prevent the entry of holes. Different absorber layers, with lead halide perovskites as only one example, will exhibit different energy levels; thus being able to tune the bandgap of the transport layer to better match the specific perovskite or other light absorber layer in use is very useful to be able to optimise a variety of solar cell designs for commercialisation. This was investigated in the context of zinc-tin oxide, a mixture of two of the most praised metal oxide electron transport layers for perovskite cells - ZnO and SnO2. The hope was that the bandgap of zinc-tin oxide, as deposited by SALD using an ozone-oxygen mixture, would vary with the Sn content (or Sn atom concentration relative to total metal atom concentration). Zinc-tin oxide was grown for the first time with SALD using different reactor head slits for each of the precursors - TDMASn and DEZ. For the oxide produced using the deposition conditions and compositions from this study, there is doubt as to whether a clear bandgap correlation with film composition was found, yet the results do point to other deposition conditions or post-deposition heat treatments that are likeliest to allow bandgap engineering, if such a relationship is valid for zinc-tin oxide. A wider range of zinc-tin oxide compositions by SALD was reported in this study than ever before (28% to 97% Sn content), and a detailed theory explaining the relationship between the deposition conditions and Sn content of the films is put forward, suggesting Sn and Zn precursor flow rates to be selected according to the desired film composition. Nor was a clear trend with composition identified for as-deposited films for transmittance, refractive index, defect and majority carrier densities, or film morphology. Photoluminescence quenching to compare the electron extraction efficiencies of different oxide compositions pointed to an Sn content of 97% being least effective. Atomic layer depositions straight onto perovskite are confirmed to be completely incompatible with the use of ozone as the oxidiser

Electrochemical removal of anodic aluminium oxide templates for the production of phase-pure cuprous oxide nanorods for antimicrobial surfaces.

Antimicrobial surfaces are ones that incapacitate or kill pathogens landing on them, which could allow for self-sanitising surfaces for hospitals or implants, ensuring healthier stays and procedures. Cuprous compounds such as Cu2O are especially effective at incapacitating both viruses and bacteria, and nanorod arrays have been shown to prevent the adhesion of pathogens and mechanically deform bacteria to the point that their cell walls rupture. A Cu2O nanorod array should therefore allow for the exploitation of both of these effects. In the present work, an electrochemical method is introduced, where Cu2O nanorods formed in a substrate-supported anodic aluminium oxide (AAO) template are held at a stable electrochemical potential throughout the removal of the AAO template. This avoids the partial reduction of the nanorods from Cu2O to Cu that was observed during chemical removal of the template, which was attributed to the presence of residual aluminium from the template fabrication process that reacts with the etchant and lowers the electrochemical potential of the nanorods to a value that favours reduction. Using the electrochemical removal method, the reliable production of phase-pure, free-standing, crystalline Cu2O nanorod arrays on ITO/glass substrates is demonstrated. This simple method is compatible with nanorod arrays of any size

Robust, Conformal ZnO Coatings on Fabrics via Atmospheric-Pressure Spatial Atomic Layer Deposition with In-Situ Thickness Control

This is the peer reviewed version of the following article: Gurbandurdyyev, G., Mistry, K., Delumeau, L. V., Loke, J. Y., Teoh, C. H., Cheon, J., Ye, F., Tam, K. C., & Musselman, K. P. (2023). Robust, conformal zno coatings on fabrics via atmospheric‐pressure spatial atomic layer deposition with in‐situ thickness control**. ChemNanoMat, 9(2)., which has been published in final form at https://doi.org/10.1002/cnma.202200498. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Zinc oxide (ZnO) is a promising material for functionalization of textiles. It can add a range of functionalities, including UV protection, antimicrobial activity, flame retardancy, hydrophobicity and electrical conductivity. Commercialization of ZnO – coated textiles is still limited due to the cost and challenges related to their manufacture. Moreover, making robust coatings on textiles and measuring their thickness is also challenging. In this work, atmospheric-pressure spatial atomic layer deposition (AP-SALD) systems are utilized for the first time to coat synthetic spun-bond polypropylene (PP) and natural cotton fabrics with ZnO. The coatings are found to be conformal and uniform, forming complete shells around the fabric fibers. The growth rate is measured to be ~0.24 nm/cycle using an in-situ reflectance setup and Virtual Interface (VI) model, which enable precise control of the coating thickness. The coatings are shown to provide UV-protection and render cotton fabric hydrophobic. No damage is observed after washing, linear abrasion, adhesion, twisting and bending tests, indicating that the coatings are robust. Aerosol-penetration tests indicate the coatings do not impact the filtering efficiency of fabrics used in N95 respirators. The results are encouraging for industrialization of the AP-SALD technique for functional textiles.The polypropylene fabrics were provided by Eclipse Automation. The authors thank Joe Paquette and Rob Shwery at Eclipse Automation for providing helpful information about the polypropylene fabrics. K.P.M. acknowledges funding from NSERC Alliance (ALLRP 554383-20), NSERC Discovery (RGPIN-2017-04212, RGPAS-2017-507977), Canada Foundation for Innovation John R. Evans Leaders Fund (Project 35552), Canada Foundation for Innovation Exceptional Opportunities Fund COVID-19 (Project 41017), and Ontario Ministry of Research, Innovation and Science Low Carbon Innovation Fund (Project Perovskite Photovoltaics)

Tuning the band gap and carrier concentration of titania films grown by spatial atomic layer deposition: a precursor comparison.

Spatial atomic layer deposition retains the advantages of conventional atomic layer deposition: conformal, pinhole-free films and excellent control over thickness. Additionally, it allows higher deposition rates and is well-adapted to depositing metal oxide nanofilms for photovoltaic cells and other devices. This study compares the morphological, electrical and optical properties of titania thin films deposited by spatial atomic layer deposition from titanium isopropoxide (TTIP) and titanium tetrachloride (TiCl4) over the temperature range 100-300 °C, using the oxidant H2O. Amorphous films were deposited at temperatures as low as 100 °C from both precursors: the approach is suitable for applying films to temperature-sensitive devices. An amorphous-to-crystalline transition temperature was observed for both precursors resulting in surface roughening, and agglomerates for TiCl4. Both precursors formed conformal anatase films at 300 °C, with growth rates of 0.233 and 0.153 nm s-1 for TiCl4 and TTIP. A drawback of TiCl4 use is the HCl by-product, which was blamed for agglomeration in the films. Cl contamination was the likely cause of band gap narrowing and higher defect densities compared to TTIP-grown films. The carrier concentration of the nanofilms was found to increase with deposition temperature. The films were tested in hybrid bilayer solar cells to demonstrate their appropriateness for photovoltaic devices

Low-temperature open-atmosphere growth of WO₃ thin films with tunable and high-performance photoresponse

Acknowledgements: Zhuotong Sun, Ming Xiao, and Judith L. MacManus-Driscoll thank the Royal Academy of Engineering grant, CIET1819_24, for funding. Subhajit Bhattacharjee thanks the Cambridge Trust (HRH The Prince of Wales Commonwealth Scholarship) for funding. Judith L. MacManus-Driscoll and Rob Jagt also thank Bill Welland for funding, as well as EPSRC grant EP/N509620/1 for funding a PhD studentship. Megan Hill thanks the Herchel Smith Foundation for a research fellowship. Kevin Musselman and Louis-Vincent Delumeau thank the Canada Foundation for Innovation Exceptional Opportunities Fund, Project 41017, for funding. The authors also thank Babak Bhakit for facilitating the ToF-ERDA analysis of the film, Yang Li on Raman characterization, and Qingshen Jing and Nives Strkalj for fruitful discussion on the figures. In-situ orientation tuning of WO3 thin films with high crystallinity is achieved with a low-temperature and open-atmosphere deposition technique. The fabricated devices showed a significant change in photo-response for film orientation.</jats:p

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

International audienc

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

International audienc