J. DuBow

Energy conversion in photoelectrochemical systems — a review

The different approaches to the conversion of solar energy into chemical and/or electrical energy employing photoelectrochemical (PEC) systems are outlined. Current work and the state-of-the-art as regards the use of various semiconductors as photoelectrodes in PEC systems and the stabilization of low band-gap semiconductors by the use of redox couples are reviewed. A critical comparison of the various approaches to the problems associated with optimal photoresponse in PEC systems indicates that electrode stabilization is the most promising amongst the alternatives currently available for efficient conversion of visible light.

Efficient photovoltaic heterojunctions of indium tin oxides on silicon

Heterojunction diodes of indium tin oxide films sputtered onto p‐silicon using ion beam techniques display significant photovoltaic effects when exposed to sunlight. Galvanomagnetic and optical measurments confirm that the oxide films are highly degenerate transparent semiconductors. At a tin oxide concentration of 10%, we observed an open‐circuit voltage of 0.51 V, short‐circuit current of 32 mA/cm2, fill factor of 0.70, and conversion efficiency of 12%. As the concentration was raised to 70%, the voltage remained steady, the current fell to 27 mA/cm2, and the fill factor fell to 0.60.

The operation of the semiconductor‐insulator‐semiconductor (SIS) solar cell: Theory

Recently 12% efficient indium tin oxide (ITO) on silicon solar cells have been reported. Experiments indicate the presence of a thin interfacial insulating layer. Thus, these devices appear to belong to a class of semiconductor‐insulator‐semiconductor (SIS) solar cells where one of the semiconductors is a degenerate wide‐band‐gap oxide. We have developed a theory in terms of minority‐carrier tunnel current transport through the interfacial layer where one semiconductor is in a nonequilibrium mode. The wide‐band‐gap semiconductor serves to block band‐to‐band majority‐carrier current and thus, in principle, give better device performance than with an MIS solar cell. The effects of interfacial layer thickness, substrate doping level, surface states and interface charge, temperature on the performance of SIS solar cells have been calculated. These indicate that real‐world ITO on silicon cells should be able to achieve 20% efficiency under AMl illumination. Other combinations of semiconductors would yield even...

The operation of the semiconductor‐insulator‐semiconductor solar cell: Experiment

We have reported on the theory of semiconductor‐insulator‐semiconductor (SIS) solar cells in a previous publication. In this paper, the fabrication and properties of indium tin oxide/p‐Si single‐crystal solar cells will be described. The ITO is deposited by the ion‐beam sputtering method. Best photovoltaic devices are obtained when the composition of indium tin oxide (ITO) is 91 mole% and 9 mole% SnO2. The device properties as a function of the ITO composition will be described. The thickness and the composition of the oxide‐silicon interface is critical for device performance. The existence of a thin interfacial layer is demonstrated by Auger spectroscopy. The effect of temperature on device performance and the spectral response are compared with the theory. The SIS model accurately matches the major trends observed in experimental nITO/p‐Si solar cells.

Thermophysical properties of oil shales

Recent developments in the characterization of the thermophysical properties of various types of oil shales are reviewed. Changes in the thermal, mechanical and electrical properties of these technologically important materials are discussed, with temperature and organic content as the experimental variables. Structural models are presented to aid in predicting the variation of thermophysical parameters with organic content in the shale. Comparison of calculated results with experimental data are shown with thermal diffusivity as a representative parameter. Areas where further research of a fundamental nature would be of particular relevance are also highlighted in the review.

Thermal analyses of Ohio bituminous coals

Abstract A suite of twenty-one bituminous coal samples from Ohio were analyzed by differential scanning calorimetry (DSC) and non-isothermal thermogravimetry (TG) techniques. Three regions of endothermic activity may be distinguished in the DSC scans in an inert atmosphere. The first peak (25–150°C) corresponds to loss of moisture from the coal, a second, very broad endotherm peaking in the range 400–500°C corresponds to devolatilization of the organic matter and a partially resolved endotherm at temperatures above 550°C probably corresponds to cracking and coking processes subsequent to the pyrolysis step. Evidence obtained from experiments with sealed pans suggest an autocatalytic effect exerted by the pyrolysis products. The use of the DSC technique to quantify the volatile matter content of coal seems less reliable than the proximate analyses obtained from non-isothermal TG in inert and O 2 atmospheres. Good agreement with ASTM values is observed by the latter method for a range of volatile matter and ash content.

Fabrication and characterization of indium tin oxide (ITO)/polycrystalline silicon solar cells

Efficient indium tin oxide (ITO)/polycrystalline silicon heterojunction solar cells have been fabricated utilizing neutralized ion‐beam sputtering techniques. These cells were fabricated on single‐pass float‐zone‐refined silicon. Conversion efficiencies of 6.25% under AM1 illumination have been observed. Cells were analyzed by I‐V characteristics and a scanning laser photoresponse technique. Qualitative minority‐carrier lifetime has been mapped using the EBIC mode of a SEM. This has revealed a reduced photoresponse at the grain boundaries independent of grain size, and also at defect clusters within individual grains. Surface blemishes and etch pits are not important in reducing the cell photoresponse. It appears that the low‐temperature processing inherent in semiconductor‐insulator‐semiconductor solar cells is applicable to polycrystalline material.

An automated frequency domain technique for dielectric spectroscopy of materials

The technique is used for measuring the dielectric properties of materials in the range from 1 MHz to 1.3 GHz is described. Modifications in the commercially available network analyser system which will permit increased accuracy and will simultaneously take into account errors arising from nonlinearities of the network analyser are also presented. The technique is demonstrated for both low- and high-loss liquids, such as carbon tetrachloride, propanol and butanol.

Antireflection properties of indium tin oxide (ITO) on silicon for photovoltaic applications

The short‐circuit current density (Jsc) of indium tin oxide (ITO/silicon solar cells has been shown both theoretically and experimentally to be a function of the thickness of the ion beam sputtered ITO layer. These results can be accounted for by computing the optical reflection from the ITO/silicon interface.

Efficient indium tin oxide/polycrystalline silicon semiconductor‐insulator‐semiconductor solar cells

Using neutralized‐ion‐beam sputtering, high‐efficiency (10.94%, AM1) and large‐area (total area, 11.46 cm2) indium tin oxide/polycrystalline silicon semiconductor‐insulator‐semiconductor solar cells have been fabricated. The important steps in the fabrication are the proper surface preparation and the incorporation of hydrogen during milling and oxidation of the substrate. The photovoltaic conversion parameters were Voc =0.526 V, Jsc =27.39 mA/cm2, and FF=0.759.