A promising route to increase the performance of hematite (alpha-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20 nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5 nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63 mA cm(-2) at 1.5 V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells.

Controlling Photoactivity in Ultrathin Hematite Films for Solar Water-Splitting

This critical review focuses on the solution deposition of transparent conductors with a particular focus on transparent conducting oxide (TCO) thin-films TCOs play a critical role in many current and emerging opto-electronic devices due to their unique combination of electronic conductivity and transparency in the visible region of the spectrum Atmospheric-pressure solution processing is an attractive alternative to conventional vacuum-based deposition methods due to its ease of fabrication, scalability, and potential to lower device manufacturing costs An introduction into the applications of and material criteria for TCOs will be presented first, followed by a discussion of solution routes to these systems Recent studies in the field will be reviewed according to their materials system Finally, the challenges and opportunities for further enabling research will be discussed in terms of emerging oxide systems and non-oxide based transparent conductors (341 references)

Solution processing of transparent conductors: from flask to film

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.

/pdf/n-type-doped-transparent-conducting-binary-oxides-an-1sftw3pood.pdf

n-Type doped transparent conducting binary oxides: an overview

The interfaces between the electrodes and the photoactive layer significantly influence the efficiency and stability of polymer solar cells (PSCs). By choosing suitable interfacial materials, the energetic barrier height at the interface could be reduced to form an ohmic contact with less series resistance, inducing high charge collection efficiency of the corresponding electrodes for holes or electrons. Solution-processable metal compounds, especially metal oxides and transition metal chelates, have the advantages of high charge carrier mobility, suitable work function, low cost, and high environmental stability, which make them attractive for applications as cathode and anode interfacial materials for efficient and stable PSCs. In this paper, we reviewed the recent progress on solution processable metal oxides and metal chelates as buffer layers in conventional and inverted PSCs. In the introduction section, we introduced the operating principles of conventional and inverted PSCs, followed by introducing the energy levels, optical properties, processing methods and characterization techniques of the buffer layers. In the second and third parts, we reviewed recent progress in materials for both anode and cathode buffer layers. Finally, we drew a conclusion and gave a perspective. We believe that solution-processable metal oxides and metal chelates will play a key role as buffer layers in the future fabrication of large area and flexible PSCs with high performance and long term stability.

Solution-processable metal oxides/chelates as electrode buffer layers for efficient and stable polymer solar cells

This work studies the effect of the sized silver (Ag) nanoparticles on the optical property of SPR. Nanoparticles were prepared on fluorine-doped-tin-oxide (FTO) coated glass substrates by RF magnetron sputtering with various deposition times and the subsequent rapid thermal annealing (RTA) to control the particle size. To make the Ag films, Ag films of different thicknesses were first deposited on either glass or FTO substrate by a vacuum sputtering technique. Some of the samples founded nanoparticles by rapid thermal annealing. The substrates with and without nanoparticles were then sensitized by immersing them in a 0.2 mM N719 dye solution. Finally, the effect of the absorption coefficient was investigated by adsorbing it on fine silver Ag islands. The surface plasmon resonance enhanced the absorption by the sample with Ag nanoparticles above that of the sample without nanoparticles. In this study, the peak position of the surface plasmon characteristic absorption increased with the grain size of the nanoparticles in a red-shift. The structure and the quantity of Ag particles were very critical to the surface plasmon resonance effect.

Size effect of Ag nanoparticles on surface plasmon resonance

Growth and characterization of antimony doped tin oxide thin films

Thin films of undoped and fluorine doped tin oxide have been prepared on borosilicate glass plates by a spray pyrolysis technique. The effect of process parameters, such as tin chloride concentration in the precursor solution, substrate to nozzle distance, carrier gas (air) flow rate, substrate temperature, and doping level of fluorine in the spray solution, on the physical properties of the tin oxide thin films have been investigated. The grown films were polycrystalline in nature above 350°C, the [110] reflection having the maximum intensity in all cases. Films of about 10−3 Ω cm resistivity and high visible transparency of about 88% have been obtained at the optimum substrate temperature of 425°C and fluorine doping concentration of 57 at.%. The optical investigations show that the optimized films have a direct allowed bandgap of 4.25 eV and indirect allowed bandgap of 2.71 eV.

Preparation and properties of sprayed undoped and fluorine doped tin oxide films

Undoped, fluorine doped and antimony doped tin oxide films are prepared on quartz plates by Spray pyrolysis technique. The films grown at the optimum substrate temperature with different doping levels have been chosen for this study. Optical properties of these films are investigated in the entire UV-Visible -IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss - Burstein effect. For fluorine doping depending upon the fluorine concentration, the absorption edge lies in the range 3.9 - 4.14 eV and for antimony doping it lies in the range 3.82 - 4.1 eV. In the undoped tin oxide films the direct allowed transition occurs at 4.02 eV and indirect allowed transition occurs at 2.43 eV, whereas for fluorine doped tin oxide and antimony doped tin oxide films, the direct allowed transitions occur in the range 4.18 - 4.28 and 4.13 - 4.22 eV respectively and the indirect allowed transitions occur in the range 2.63 - 2.73 and 2.54 - 2.65 eV respectively. Optical properties near the plasma edge have been analyzed using Drude's theory. The dependence of effective mass on carrier concentration has been explained on the basis of nonparabolicity of the conduction band. The shift in the fermi energy, calculated on the basis of energy dependent effective mass, is consistent with the measured shift in the absorption edge.

S. Shanthi

Papers

Growth and characterization of antimony doped tin oxide thin films

Preparation and properties of sprayed undoped and fluorine doped tin oxide films

Investigations on the Optical Properties of Undoped, Fluorine Doped and Antimony Doped Tin Oxide Films

Effect of fluorine doping on structural, electrical and optical properties of sprayed SnO2 thin films

Role of defects on the nonlinear optical properties of La doped Bi2WO6 nanostructures for optical device applications