GaAs cell

Two different high efficiency types of GaAs cell stmctures ate being developed. These are GaAs homojunctions with a top window layer of Ga ... 

GaAs cells can also operate at relatively high temperatures without the performance degradation that silicon and many other semiconductors experience. This allows GaAs cells to be suitable for concentrating PV systems. 

Cells made from GaAs are more costly than silicon cells, because the production process is not as well developed, and gallium and arsenic are not abundant materials. GaAs cells have been used when very high efficiency is needed regardless of cost such as required in space applications. They were also used in the Sunraycer, a photovoltaic-powered electric car, which won the Pentax World Solar Challenge race for solar-powered vehicles in 1987. It ran the 3000-km from Darwin to Adelaide, Australia at an average day time speed of 66-km per hour. The 1990 race was won by a... 

At present, the only photochemical storage system which satisfies nearly all of these conditions is the reaction of photosynthesis however, certain photovoltaic cells such as the silicon and GaAs cells, satisfy many of the requirements for direct conversion to electricity. In addition, there are several possible systems which have a potential to satisfy most of the requirements and will be considered in this article. 

GaAs cells have often been used when very high efficiency is needed regardless of cost as required in space applications. This was also the case with the Sunraycer, a photovoltaic-powered electric car, which in 1987 won the Pentax World Solar Challenge race for solar-powered vehicles. It... 

Other fectors that influence the output of solar cells are degradation of surfeces and of electrodes the first causes a reduction of carrier Ufetime, the second causes a reduction in solar cell life expectancies. An example of the first is the beneficial effect of a natural oxide layer that reduces surface recombination of Si solar cells, while special efforts need to be made for GaAs cells to passivate the surfece. An example for the second effect is the CdTe solar cell, which has difficulties maintaining stable electrodes on the p-type side. 

Each of the cells in the Table 3 exhibits an open-circuit photopotential significantly greater than the minimum potential necessary to split water. The majority of these cells can generate a photopotential in excess of 2 volts. An unnecessary Kmit of one multiple band gap photoexcitation per electrolysis would under-utilize Vphoto. diminishing )electrolysis- For example, a GaInP/GaAs cell has a maximum power photopotential of 2.0 to 2.1 V and an open-circuit potential of 2.3 V [12]. Two... 

The characteristics of Schottky barriers between P(Ac) and various low work function metals under white light illumination are summarized in Table 23-1 [961-971]. Conversion efficiencies are however low maximum efficiencies are only ca. 0.3 % to 1.1 %. Table 23-3 summarizes junction parameters for Schottky barriers and heterojunctions based on interfacing P(Ac) to inorganic semiconductors [961, 972-976, 982]. These inorganic semiconductor/P(Ac) cells were found to have higher conversion efficiencies, ca. 6.2%, as compared to Au/GaAs cells, ca. 4.6%. 

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