Reduction In Open-circuit Voltage Research Articles

Scanned laser response studies of metal-insulator-silicon solar cells in polycrystalline czochralski silicon

Metal-insulator-silicon (MIS) solar cells with and without grain boundaries were fabricated using polycrystalline Czochralski silicon. Scanned laser spot methods were used to provide high resolution photocurrent and surface reflection images of these cells. Electrically active grain boundaries, revealed by suppressed photocurrent collection, did not correlate perfectly with etc-produced surface features. For the laser wavelength (6328 Å) an effective photocurrent loss of 30–40% occurred over a 16μm width grain boundaries. Comparisons of short-circuit current versus open-circuit voltage over a wide range of irradiance values were made on cells with and without grain boundaries. For a typical polycrystalline cell the air mass one photocurrent loss was 8%, whereas a 3% loss was determined for the laser excitation. The open-circuit voltage reduction was about 25mV, implying an opposing current density associated with grain boundary walls of about 50% of that for the MIS barrier. This work shows the value of combining scanned light spot methods with photovoltaic characterization using cells with and without active grain boundaries. Future extensions should allow studies of detailed grain boundary electrical behavior including procedures to modulate it.

Theoretical effects of surface diffused region lifetime models on silicon solar cells

A computer simulation of silicon solar cells has indicated that the combination of band gap reduction due to heavy doping and certain spatial forms of lifetime dependence can combine to form severe limitations to the open circuit voltage of silicon solar cells. The interaction of these effects tends to shift the active region of the diffused surface layer away from the injecting junction resulting in an increase in the current density injected into the surface region. Reductions in open circuit voltage as great as 10% over models which do not include these effects can be seen.

Technology of GaAs metal—Oxide—Semiconductor solar cells

The growth of an oxide interfacial layer was recently found to increase the open-circuit voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> ) and efficiency by up to 60 percent in GaAs metal-semiconductor solar cells. Several oxidation techniques have been developed which will provide the necessary oxide thickness and chemical structure. Details of these techniques using ozone, water-vapor-saturated oxygen, or oxygen gas discharges are described, as well as apparent crystallographic orientation effects. Preliminary results of the oxide chemistry obtained from X-ray, photoelectron spectroscopy are given. Ratios of arsenic oxide to gallium oxide of unity or less seem to be preferable. Samples with the highest V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> predominantly have As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> in the arsenic oxide rather than As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+5</sup> . A major difficulty at this time is a reduction in open-circuit Voltage by 100-200 mv when the antireflection coating is vacuum deposited. Without this effect, values of about 750 mV for V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> and 15-percent efficiency with air mass of 1 sun can be obtained with single-crystal GaAs. All techniques are compatible with polycrystalline GaAs thin films.

Effect of the Internal Short-Circuiting on Electrical Characteristics of MHD Power Generators with Peg Walls

The effect of the internal short-circuiting, which is caused by metal pegs embedded in insulating walls for an MHD power generator results in the reduction in open-circuit voltage, whereas it does not make any change in short-circuited current in the absence of the Hall effect. Electrical characteristics of generators with peg walls are expressed in terms of a correction factor which represents a rate of the reduction in open-circuit voltage. It is shown that this factor can be determined theoretically by the use of a conformal mapping technique or experimentally by means of an electrolytic bath. Experimental results obtained with a combustion-driven MHD power generator reveal that this effect is not minor even in the presence of thermal boundary layers near peg walls and that it can be minimized by coating alumina on the surface of metal pegs.