Interface contribution to GaAs/Ge heterojunction solar cell efficiency

Journal Article · Sat Jul 01 04:00:00 EDT 1989 · IEEE Transactions on Energy Conversion; (USA)

DOI:https://doi.org/10.1109/16.30928· OSTI ID:5278885

Bullock, J N; Wu, C H ^[1]; Wise, J F ^[2]

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1. Missouri Univ., Rolla, MO (USA). Dept. of Electrical Engineering
2. Aero Propulsion Lab., Wright-Patterson Air Force Base, Dayton, OH (US)

A solar cell formed by growing a p-on-n AlGaAs/GaAs heteroface homojunction on a thin Ge substrate is studied by investigating the contribution of the GaAs/Ge heterostructure to the solar-cell efficiency. The existence of interface states is required in the absence of a Ge p-n junction in order to produce the photovoltaic effect with an open-circuit voltage enhancement as experimentally observed. Dark current-voltage characteristics of the GaAs/Ge heterojunction are calculated when the carrier transport is by thermionic emission and tunneling mechanisms. The authors' evaluations correctly explain the observed changes of efficiency, the decrease of fill factor, the increase of open-circuit voltage, and the insignificant change of short-circuit current as compared to a GaAs/GaAs solar cell. If the short-circuit current from the heterojunction is of the order of 25 m/sup A//cm/sup 2/, which is less than that of the p-n junction cell, the reduction of the solar cell efficiency is about 0.5 to 1.5 percent over a wide range of GaAs/Ge doping concentrations. Very few interface states tend to yield a diodelike dark I-V relation, and this behavior in the reverse-biased region will degrade the fill factor while soft breakdown in the reverse-biased region will improve the fill factor. The efficiency is controlled by the forward-biased part of the dark I-V curve. However, if the short-circuit current of the heterojunction is greater than that of the p-n junction cell, the more the interface charge, the better the combined solar cell efficiency. Their results differ from the assertion that a Ge p-n junction is responsible for the open-circuit voltage increase.

• OSTI ID: 5278885
• Journal Information: IEEE Transactions on Energy Conversion; (USA), Journal Name: IEEE Transactions on Energy Conversion; (USA) Vol. 36:7; ISSN 0885-8969; ISSN ITCNE
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
140502 -- Solar Energy Conversion-- Thermonic & Thermoelectric conversion
ALLOYS
CARRIER MOBILITY
DATA
DIRECT ENERGY CONVERTERS
DOPED MATERIALS
EFFICIENCY
EMISSION
EQUIPMENT
EXPERIMENTAL DATA
GALLIUM ARSENIDE SOLAR CELLS
GERMANIUM ADDITIONS
GERMANIUM ALLOYS
HETEROJUNCTIONS
HOMOJUNCTIONS
INFORMATION
JUNCTIONS
MATERIALS
MOBILITY
NUMERICAL DATA
OPTICAL PROPERTIES
P-N JUNCTIONS
PHOTOELECTRIC CELLS
PHOTOELECTROMAGNETIC EFFECTS
PHOTOVOLTAIC CELLS
PHOTOVOLTAIC EFFECT
PHYSICAL PROPERTIES
SEMICONDUCTOR JUNCTIONS
SOLAR CELLS
SOLAR EQUIPMENT
SUBSTRATES
THERMIONIC EMISSION
TUNNELING