Translation effects in fluorine doped tin oxide thin film properties by atmospheric pressure chemical vapor deposition

In this work, the impact of translation rates in fluorine doped tin oxide (FTO) thin films using atmospheric pressure chemical vapour deposition (APCVD) were studied. We demonstrated that by adjusting the translation speeds of the susceptor, the growth rates of the FTO films varied and hence many of the film properties were modified. X-ray powder diffraction showed an increased preferred orientation along the (200) plane at higher translation rates, although with no actual change in the particle sizes. A reduction in dopant level resulted in decreased particle sizes and a much greater degree of (200) preferred orientation. For low dopant concentration levels, atomic force microscope (AFM) studies showed a reduction in roughness (and lower optical haze) with increased translation rate and decreased growth rates. Electrical measurements concluded that the resistivity, carrier concentration, and mobility of films were dependent on the level of fluorine dopant, the translation rate and hence the growth rates of the deposited films

Chemical and physical vapour deposition of optoelectronic metal oxide thin films

Metal oxide thin films feature prominently in virtually every optoelectronic device including photovoltaics, for harnessing solar energy, and LED displays, as seen ubiquitously in every smartphone, television, smartwatch, information display, etc.. These materials perform an important function in such devices as transparent electrodes enabling the flow of current through the device whilst permitting incident or emitted light to pass freely and uncoloured between the central optoelectronic element and the external medium. Such materials are known as transparent conducting oxides (TCOs), and owe their transparency to a wide optical band gap exceeding the energy of visible photons (> 3.1 eV), and their electrical conductivity to a sufficiently high free electron density and mobility. Free electrons in these materials originate from crystal defects, which can be deliberately introduced by doping. Transition metal (TM) dopants have recently come to light as enabling greater electron mobility in TCOs compared to traditional main- group dopants, while widening their optical transparency window into both the UV and IR. The commercial standard TCO material for most applications is Sn-doped In2O3, therefore the first objective of this thesis is to explore and compare to Sn some transition metal dopants (Zr, Hf, Mo) for In2O3 in terms of electronic and optical behaviour. The commercial supply risk associated with indium, being a naturally scarce element, leads to the second objective, which is to explore TM doping of SnO2 using Ta. This is carried out using commercial scale-up syntheses via atmospheric-pressure chemical vapour deposition (APCVD) with a view to creating a more competitive indium-free TCO. Finally, gallium(III) antimonates (Ga2xSb2-2xO4) are explored via APCVD as ternary indium- free, wide-bandgap host matrices for TCO and TFT applications

Improved FTO/NiOx interfaces for inverted planar triple cation perovskite solar cells

Front electrodes of fluorine doped tin oxide (FTO) thin films and hole transporting layers of nickel oxide thin films have been combined to fabricate 1.063 cm2 inverted planar solar cells with cesium-containing triple cation perovskites as absorber layers. Using atmospheric pressure chemical vapor deposition FTO layers were obtained with low sheet resistance, decreased root mean squareroughness, increased transmission,and reduced optical haze values compared to a widely used commercial FTO substrate. Cell performance outperformed the equivalent cells fabricated using the commercial FTO. With full illumination under maximumpowerpoint tracking, a stabilized power conversion efficiency of 13.78 % was obtained for the champion device

n-Type doped transparent conducting binary oxides: an overview

This article focuses on n-type doped transparent conducting binary oxides – namely, those with the general formula MxOy:D, where MxOy is the host oxide material and D is the dopant element. Such materials are of great industrial importance in modern materials chemistry. In particular, there is a focus on the search for alternatives to indium-based materials, prompted by indium's problematic supply risk as well as a number of functional factors. The important relationship between computational study and experimental observation is explored, and an extensive comparison is made between the electrical properties of a number of the most interesting experimentally-prepared materials. In writing this article, we aim to provide both an accessible tutorial of the physical descriptions of transparent conducting oxides, and an up-to-date overview of the field, with a brief history, some key accomplishments from the past few decades, the current state of the field as well as postulation on some likely future developments

APCVD of dual layer transparent conductive oxides for photovoltaic applications

We report the atmospheric pressure chemical vapour deposition (APCVD) of a dual layer transparent conductive oxide (TCO). This combines a fluorine doped tin oxide (FTO) base layer with a fluorine doped zinc oxide (FZO) top layer, where we seek to utilise the respective advantages of each material and the differences in their associated industrial deposition process technologies. Deposition of a 250 nm thick FZO layer on FTO was enough to develop features seen with FZO only layers. The crystallographic orientation determined by the FZO dopant concentration. Changes to the deposition parameters of the underlying FTO layer effected stack roughness and carrier concentration, and hence optical scattering and absorption. Photovoltaic cells have been fabricated using this TCO structure showing promising performance, with efficiencies as high as 10.21% compared to reference FTO only values of 9.02%. The bulk of the coating was FTO, providing the majority of conductivity and the large surface features associated with this material, whilst keeping the overall cost low by utilising the very fast growth rates achievable. The FTO was capped with a thinner FZO layer to provide a top surface suitable for wet chemical or plasma etching, allowing the surface morphology to be tuned for specific applications

Influencing FTO thin film growth with thin seeding layers: a route to microstructural modification

We report on the seeded growth of fluorine doped tin oxide (FTO) polycrystalline transparent conducting oxide (TCO) thin films on float glass using a novel two-step chemical vapour deposition (CVD) method. Aerosol-assisted CVD (AACVD) was used to grow a seed layer to direct and promote full film growth via an atmospheric pressure CVD (APCVD) overlay. The method allowed for reproducible control over morphology and denser, rougher, higher-performing TCO at a relatively low growth temperature (500 °C). Growth promotion depended on seeding time with an optimal seeding time being present, below which morphology control and conformal coverage was unavailable. The film properties and functional characteristics were characterised by SEM, AFM, XRD, XPS, UV-Vis-Near IR transmittance-reflectance and Hall Effect probe measurements. Highly transparent and electrically conductive films, comparable to commercial materials and with high roughness and low transmission haze values indicate the process yields high quality films with a controllable morphology that can be tuned to desired application. The versatile method provides a route towards the morphological control of high-quality FTO thin films with high optical clarity and low-emissivity properties and can be readily extended to a variety of different substrates and metal oxide materials

Thin Films of Tin Sulphide for Application in Photovoltaic Solar Cells

Tin sulphide (SnS) is a promising new material for use in photovoltaic solar cells. With a direct energy band gap of about 1.3 eV, and a high optical absorption coefficient, only a few microns of SnS are needed to absorb most of the incident light. Not only is SnS made of abundant, environmentally acceptable elements, it is also amphoteric giving flexibility to device design. Structures that can be envisioned include p-type SnS (absorber layer) / n-type (window layer) heterojunction devices, buried p-n junction devices made using SnS and p-i-n structure devices where the i-layer is SnS. It is most likely that the grain boundaries in SnS can be passivated either by counter-doping the grain boundaries, or by oxidizing the grain boundaries to form wide energy bandgap n-type SnO2 within p-type SnS, as dopants or oxygen will diffuse preferentially down the grain boundaries and react first at the grain boundary surfaces. Thin film solar cell devices based on the use of SnS have now been produced with efficiencies > 2 %; these and other promising results indicate that it is most likely that devices with efficiencies > 10% will be produced in the near future. Given that tin layers are routinely coated in industry over large area substrates and that industrial sulphidization processes are also well established, the industrialization of this technology should be more straightforward than that encountered with the already commercialised cadmium telluride and copper indium gallium diselenide thin film technologies. This review discusses the chemical and physical properties of SnS, the methods of producing both bulk crystals and thin films of SnS, the literature available on studies of SnS2 based photovoltaic solar cell devices, and progress made so far in developing this exciting new material

Advances in Chemical Vapor Deposition

Pursuing a scalable production methodology for materials and advancing it from the laboratory to industry is beneficial to novel daily-life applications. From this perspective, chemical vapor deposition (CVD) offers a compromise between efficiency, controllability, tunability and excellent run-to-run repeatability in the coverage of monolayers on substrates. Hence, CVD meets all of the requirements for industrialization in basically all areas, including polymer coatings, metals, water-filtration systems, solar cells and so on. The Special Issue “Advances in Chemical Vapor Deposition” is dedicated to providing an overview of the latest experimental findings and identifying the growth parameters and characteristics of perovskites, TiO2, Al2O3, VO2 and V2O5 with desired qualities for potentially useful devices