Electro-optical Properties Of Thin Films Research Articles

Influence of Pb2+ doping in the optical and electro-optical properties of SnO2 thin films

Different types of doping incorporated to tin dioxide (SnO2) have been reported in order to control its bandgap aiming optoelectronic applications, such as transparent electrodes, solar cells and displays. In this work, the doping of SnO2 with lead in the oxidation state 2+ (Pb2 +) is investigated, in conjunction with the influence on the optical and electro-optical properties of thin films, deposited by sol-gel-dip-coating. It was observed that for an insertion up to 25 at% of lead, there is no formation of a secondary crystalline phase beyond the rutile phase of SnO2. Optical characterization data indicate two behavior tendencies: for doping level up to 1 at%, Pb2+ enters preferentially as interstitial impurity, whereas for higher doping it enters substitutional to Sn4+. For doping up to 1 at% the bandgap increases due to the Burnstein-Moss effect, in addition to a decrease in the capture energy for metastably photoexcited electrons. On the other hand, for doping above 1 at%, there is an increase in the Urbach energy, shifting the energy level of the valence band, leading to a decrease in the bandgap from 3.45 to 2.89 eV, which shows potential applicability in bandgap engineering. The higher doping level also increases the capture energy for photoexcited electrons and gives rise to the persistent photoconductivity effect at low temperatures, related to a large lattice relaxation around the dominant photoexcited defect.

Comparison of Structural and Electro-optical Properties of Thin Films Fabricated for Different Deposition Times Using TiO2 Precursor Solutions with and without HCl by Ultrasonic Spray Pyrolysis

In this report, two different TiO2 solutions with and without HCl were, firstly, prepared. Then, totally twelve number of thin film samples were obtained using these solutions for each of these two different group films by ultrasonic spray pyrolysis (USP). Of these twelve samples, each of the four was created at three different spray times (25, 50, 75 min), respectively, and they were annealed at 500 C. Structural, morphological, and electro-optical properties of TiO2 thin films were performed by X-ray diffractometer (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), and ultraviolet-visible spectrophotometer (UV-VIS). It was seen that the HCl addition improves the crystallinity of the thin film samples dramatically even though at low deposition temperatures. HCl addition causes densification on the surface of the films and these films also exhibited the best morphological and structural properties compared to thin films without HCl. Also, the bandgap values of all thin films prepared with and without HCl decreases from 3.40 to 3.21 eV and 3.29 to 3.15 eV, respectively. Increase in the thickness of films by the addition of HCl plays a vital role on the morphological, structural, and electro-optical properties of the samples.

Photoresponsive azo-doped aerosil/7CB nematic nanocomposites: the effect from concentration of the azobenzene photoactive agent

We studied nanomaterials composed from 3 wt.% aerosil nanospheres and the room-temperature nematic liquid crystal 4-n-heptyl cyanobiphenyl (7CB), as doped with the photoactive liquid crystal 4-(4'-ethoxyphenylazo)phenyl hexanoate (EPH). The molecules of the azobenzene photoactive agent EPH were included at concentration ranging from 1 wt.% to 10 wt.%. The object of our interest is the effect of the EPH amount on the photosensitized electro-optical properties of thin films of aerosil/7CB/EPH nematic nanocomposites.

Tuning the polarity and surface activity of hydroxythiazoles – extending the applicability of highly fluorescent self-assembling chromophores to supra-molecular photonic structures

Processing of 4-alkoxythiazole sulfonamidesviathe Langmuir–Blodgett technique gave an insight into the influence of aggregation on the electro-optical properties of thin films.

Indium–tin-oxide coatings for applications in photovoltaics and displays deposited using rotary ceramic targets: Recent insights regarding process stability and doping level

Several aspects related to high power sputtering with industrial scale sintered ceramic rotary indium–tin-oxide (ITO) targets are presented in the first part of this paper. In particular, the process stability and target integrity upon sputtering with ≥20kW/m power load and the influence of the gap size between cylindrical segments are discussed. Results show that, in order to avoid nodule formation and deposition rate fluctuations, direct current (DC) power load needs to be limited well below 20kW/m over long sputter runs. Additional work demonstrates that at a gap size at or below 0.15mm, strongly adhering deposits form readily between cylindrical segments which are not observed with standard 0.35mm gaps.The influence of Sn doping level on electro-optical properties of thin films targeting an application such as hetero-junction c-Si solar cells is also investigated. Again, rotary targets operated at high power (10kW/m) are used, including standard grade ITO containing 10wt.% SnO2 and another composition with only 3wt.% SnO2. The influence of H2 and different concentrations of O2 in the sputter gas is analysed for both target materials. Results indicate that although coatings derived from the lower-doped ITO exhibit considerably less absorption in the NIR due to lower carrier concentrations, their resistivity is nearly 30% higher than that from the standard ITO coating.

Transmission and small-angle scattering of light by nematic liquid crystal-cellulose diacetate composite with self-organized structure

Electrooptical properties of thin films of nematic liquid crystal-cellulose diacetate (NLC-CD) composite with self-organized structure. The composite samples were prepared at different rates of solvent evaporation on substrates inclined at various angles. The best optical contrast is obtained in composite films formed on substrates inclined at 45°. The dependence of the small-angle scattering of light on the control electric field strength in the NLC-CD composite differs from the analogous dependence known for the traditional polymer-dispersed liquid crystal composites. It is established that the classical theory of the small-angle scattering does not adequately describe structural characteristics of the NLC-CD composite with self-organized structure.

Compositional and Electric Field Dependence of the Dissociation of Charge Transfer Excitons in Alternating Polyfluorene Copolymer/Fullerene Blends

The electro-optical properties of thin films of electron donor-acceptor blends of a fluorene copolymer (PF10TBT) and a fullerene derivative (PCBM) were studied. Transmission electron microscopy shows that in these films nanocrystalline PCBM clusters are formed at high PCBM content. For all concentrations, a charge transfer (CT) transition is observed with absorption spectroscopy, photoluminescence, and electroluminescence. The CT emission is used as a probe to investigate the dissociation of CT excited states at the donor-acceptor interface in photovoltaic devices, as a function of an applied external electric field and PCBM concentration. We find that the maximum of the CT emission shifts to lower energy and decreases in intensity with higher PCBM content. We explain the red shift of the emission and the lowering of the open-circuit voltage (V(OC)) of photovoltaic devices prepared from these blends with the higher relative permittivity of PCBM (epsilon(r) = 4.0) compared to that of the polymer (epsilon(r) = 3.4), stabilizing the energy (E(CT)) of CT states and of the free charge carriers in blends with higher PCBM concentration. We show that the CT state has a short decay time (tau = ca. 4 ns) that is reduced by the application of an external electric field or with increasing PCBM content. The field-induced quenching can be explained quantitatively with the Onsager-Braun model for the dissociation of the CT states when including a high electron mobility in nanocrystalline PCBM clusters. Furthermore, photoinduced absorption spectroscopy shows that increasing the PCBM concentration reduces the yield of neutral triplet excitons forming via electron-hole recombination, and increases the lifetime of radical cations. The presence of nanocrystalline domains with high local carrier mobility of at least one of the two components in an organic heterojunction may explain efficient dissociation of CT states into free charge carriers.

Electro-optical properties of thin indium tin oxide films: Limitations on performance

This work has been concerned with the measurement and analysis of the electro-optical properties of thin films of indium tin oxide deposited by ion beam sputtering. In the present context, the principal use of these films is for window layer solar cells, and it is necessary to have an accurate knowledge of the optical and electrical properties, and of their dependence on deposition conditions, to enable realistic predictions of the internal quantum efficiency to be made. We have measured the properties of films as a function of deposition rate, partial pressure of oxygen in the sputtering gas and annealing temperature. The properties studied are the variation with wavelength of the optical constants, the Hall mobility, the film structure and composition. The compositional data (from X-ray photoemission spectroscopy) suggest that heat treatment changes the state of oxidation of tin from SnO to SnO 2− x , the oxygen vacancies acting as doubly ionized donors. At high partial pressures of oxygen and low densities of free carriers, the mobility is limited by grain boundary scattering, the magnitude of which is determined by the deposition conditions. For ennealed films with higher carrier densities, the optical and electrical data suggest that ionized impurity scattering is the mechanism limiting the mobility. These two mechanisms thus appear to impose a lower limit on the resistivity achievable in this material.