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IMPROVED HIGH EFFICIENCY p-p-n GaAlAs-GaAs-GaAs SOLAR CELLS

IP.com Disclosure Number: IPCOM000036218D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Pollak, FH: AUTHOR [+2]

Abstract

Current p-p-n GaAlAs-GaAs-GaAs solar cells operate at AMI efficiencies of 21-22%. The theoretical limit for this cell is 27-28%. A major loss component is a low quantum efficiency for converting photons into current in the 2.5-3.2 eV region of the solar spectrum. This is shown in Fig. 1 which shows the spectral response of a state-of-the-art cell. Even though this is considered to be a "good" cell, further improvement is desired for concentrator applications where the cost of generating power is limited by the efficiency of the cell rather than its cost. Therefore, the 5-6 percentage points improvement which are theoretically possible are worthwhile achieving.

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IMPROVED HIGH EFFICIENCY p-p-n GaAlAs-GaAs-GaAs SOLAR CELLS

Current p-p-n GaAlAs-GaAs-GaAs solar cells operate at AMI efficiencies of 21-22%. The theoretical limit for this cell is 27-28%. A major loss component is a low quantum efficiency for converting photons into current in the 2.5-3.2 eV region of the solar spectrum. This is shown in Fig. 1 which shows the spectral response of a state-of-the-art cell. Even though this is considered to be a "good" cell, further improvement is desired for concentrator applications where the cost of generating power is limited by the efficiency of the cell rather than its cost. Therefore, the 5-6 percentage points improvement which are theoretically possible are worthwhile achieving.

The loss mechanism associated with the cell of Fig. 1 can be explained by the band diagram of Fig. 2 which portrays the optoelectronic

(Image Omitted)

behavior of the cell. The important points of this figure are: (1) EF, the Fermi level pinning position, is mid-gap 1.0 eV from a band edge and (2) the p-GaAlAs layer is depleted of free carriers. The consequence of this is that most of the photogenerated electrons in the GaAlAs layer will experience a drift field which drives electrons towards the GaAlAs surface where they are lost by being trapped by surface states rather than being driven toward the GaAs p-n junction where they would contribute to photocurrent.

An improvement is achieved by the use of a transparent electrode on the GaAlAs surface,...