Laxmikant Damodare

Optical and electrical investigations of indium oxide thin films prepared by thermal oxidation of indium thin films

Indium oxide thin films have been prepared by thermal oxidation of vacuum‐deposited indium thin films in air in an open furnace at about 600 K. These indium oxide thin films prepared by thermal oxidation have been examined for optical transparency by measuring their optical absorbance as a function of wavelength. From the optical absorption data, optical band gap and the nature of the forbidden energy gap in the indium oxide thin films have been determined. Electrical conductivity measurements have also been carried out on the above oxide films as a function of temperature during heating and cooling cycles in vacuum. It is found that after the first heating, electrical conductivity increases to a significant extent due to removal of point defect clusters due to annealing which contribute to both carrier generation and scattering. From the thermoelectric power measurements carried out, it has been concluded that electrons are the majority carriers in these indium oxide thin films.

EFFECT OF SURFACE TREATMENT ON AN N-CDSE0.6TE0.4 THIN-FILM PHOTOANODE/POLYSULPHIDE ELECTROLYTE SOLAR CELL

Polycrystalline thin films of n-CdSe0.6Te0.4 were deposited in a vacuum of 5×10−5 Torr by thermal flash evaporation with a deposition rate of 20±1 A/s on indium oxide coated glass plates [σ=1.25×104 (Ω cm)−1] held at 200 °C. Application of surface treatment techniques such as annealing and photoelectrochemical etching on the films revealed that the films exhibit photoelectrochemical behavior with increased conversion efficiency and stability after treatment. Gartner’s model [Phys. Rev. 116, 84 (1954)] was used in the calculation of the solid state parameters of the films like the carrier concentration ND and minority carrier diffusion length Lp for different surface treatments. Chemical etching improves the efficiency and fill factor from 1.53% and 40% to 2.72% and 50% respectively, whereas photoelectrochemical etching improves further the efficiency to 3.83% and fill factor to 59% and the stability of the photoelectrode in the polysulphide electrolyte.

A study of band-bending and barrier height variation in thin film n-CdSe0.5Te0.5 photoanode/polysulphide junctions

Polycrystalline thin films of n-CdSe0.5Te0.5 were deposited in a vacuum of 5 × 10−5 torr by thermal flash evaporation with a deposition rate of 20 ± 1 As−1 on indium oxide coated glass plates [σ = 1.25 × 104 (Ωcm)−1] held at a temperature of 473 K. The change in the pH value of the polysulphide electrolyte from 12.5 to 8.0 leads to a fall in the extent of band bending from 680 meV to 420 meV and decrease in the barrier height from 690 meV to 430 meV. The barrier heights as calculated from Mott-Schottky plots and current-voltage plots are compared. From the reverse saturation current (I0) variation with temperature, it is found that the barrier height decreases from 690 meV to 430 meV with decrease in pH of the electrolyte from 12.5 to 8.0. The variation of diode ideality factor n, with temperature was also studied. It was found that the diode ideality factor n, decreases with increase of temperature, viz. from 3.00 to 2.00 with rise in temperature from 300 K to 333 K. This is due to the additional injection of electrons from the bulk into the junction region because of increase in temperature.

A study of substrate variation effects on the properties of n-CdSe0.7Te0.3 thin film/polysulphide photoelectrochemical solar cells

Abstract The effect of substrate on the working of n-CdSe 0.7 Te 0.3 thin-film/polysulphide photoelectrochemical (PEC) solar cells has been investigated in detail. The role of substrates like stainless steel and In 2 O 3 -predeposited glass slides on the Mott-Schottky plots is investigated at various frequencies for various surface treatments using both types of substrates and the reasons for the dispersion observed have been explained. The variation of space-charge capacitance (at a fixed electrode potential) as a function of frequency has been investigated and also the power law governing the capacitance dependence. The improvement in the power output characteristics on annealing and photoelectrochemical etching occurs due to the reduction of surface states, leading to a decrease in trap states.

Effect of annealing and surface treatment on the efficiency of photoelectrochemical (PEC) solar cells with vacuum-deposited n-InSe thin film electrode

Abstract Three hundred-nanometre thick films of n-InSe have been vacuum-deposited by flash evaporation on conducting indium oxide film coated clean glass substrates held at 373 K at 6.6 × 10−3 Pa pressure. These InSe films have been used as photoelectrodes in a photoelectrochemical (PEC) cell with graphite as the counter electrode, the saturated calomel electrode as the reference electrode and aqueous polyiodide electrolyte (with different pHs) as the redox electrolyte. PEC cells have been characterised by making I–V and C-V measurements under different experimental conditions, i.e., using the as-grown InSe films as photoelectrodes before and after surface treatment and after annealing and/or etching and for different pHs of the electrolyte. The optimum pH has been found to be about 6.2. It is also found that surface treatment and annealing leads to increase in the efficiency of the PEC solar cell. The open circuit voltage and photo current density are found to be of the order of 580 mV and 3000 μA/cm2, respectively under AM1 condition.

Power conversion efficiency studies of vacuum evaporated n-CdSe0.6Te0.4 semiconducting thin film/(aq) ferro-ferricyanide electrolyte photoelectrochemical solar cells

Abstract Photoelectrochemical (PEC) solar cells made using as-grown polycrystalline thin films of n-CdSe0.6Te0.4 (thickness ≈ 5000 A) (prepared by vacuum thermal flash evaporation with a deposition rate of 20 ± 1 A s −1 in a vacuum better than 5 × 10−5 torr on indium oxide coated microslide glass plates [ σ = 1.25 × 10 4 (Ω- cm ) −1 ] held at 200°C) dipped in aqueous ferro-ferricyanide electrolyte have been studied to evaluate the conversion efficiency under white light illumination intensity of 100 mW cm−2 (AM1). Mott-Shottky plots have been drawn (in the dark condition) to evaluate the semiconductor parameters. The reasons for the observed high power conversion efficiency and high quantum efficiency in relation to the semiconductor parameters are explained. The films have been characterized by X-ray diffraction for structural studies, Energy Despersive Analysis of X-rays (EDAX) for compositional analysis, Scanning Electron Microscopy (SEM) technique for surface morphology studies and optical absorption for band gap determination.

Characterization of n-CdSe0.7Te0.3/(aq) Polyiodide Energetic Interface and Photoelectrochemical Studies

The vacuum deposited thin films of n-CdSe0.7Te0.3 of 5000 A thickness have been characterized by X-ray diffraction (XRD) for structural analysis, by energy despersive analysis of X-rays (EDAX) for compositional analysis and the scanning electron microscopy (SEM) for surface studies. Similar films have been deposited on Indium Oxide precoated microslide glass plates and the photoelectrochemical properties of n-CdSe0.7Te0.3/polyiodide junction are investigated for suitability for solar energy conversion by I–V measurements in the dark. Also, the carrier concentration and flat band potential have been calculated from the space charge capacitance vs voltage measurements. The minority carrier diffusion length, Lp has been determined using Gartners model. Using the Mott-Schottky plots, the energy band diagram at flat band condition has been constructed. The occurrence of high quantum efficiency and high power conversion efficiency have been explained.

Photoelectrochemical investigations on vacuum deposited n-CdSe0.6Te0.4 thin film/polysulphide photoelectrochemical solar cells using stainless steel substrates

Abstract Thin films of n -CdSe 0.6 Te 0.4 of thickness ≈500 nm were deposited by vacuum flash evaporation on highly conducting, precleaned stainless steel substrates (thickness = 2 mm) kept at 473 K at a pressure of 6.6 × 10 −3 Pa. The as-grown films exhibited photoactivity in (aq) 1 M NaOH1 M Na 2 S1 M S (pH = 12.6) The onset of photocurrent with increase in applied electrode potential on illumination of the photoelectrochemical cell at an intensity of 100 mW/cm 2 white light yielded a flat band potential of ≈−1200 mV versus saturated calomel electrode (SCE). It was found from the power output characteristics that the efficiency of the photoelectrochemical (PEC) cell using as- grown films on these substrates was about 2.2%. Using Gartners Model, the donor concentration and the minority carrier diffusion length were found to be 3.43 × 10 17 cm −3 and 0.046 μ m respectively which indicated the good rectifying nature of n -CdSe 0.6 Te 0.4 thin film/ polysulphide junction and large grain size and good conductivity of the stainless steel substrate.