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US 4,366,334 AGranted
Photovoltaic cell usable as a solar cell
AssigneeThomson-CSF
InventorsBaudouin de Cremoux, Pierre Poulain, Nicole Sol
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AssigneeThomson-CSF
InventorsBaudouin de Cremoux, Pierre Poulain, Nicole Sol
Estimating the term…
The invention relates to a low cost photovoltaic cell, using a minimum thickness layer of semiconductor compounds able to provide the photovoltaic effect and specifically in polycrystalline form. On a molybdenum sheet an auxiliary polycrystalline germanium layer is deposited in order to facilitate subsequent depositions. This is followed by an intermediate polycrystalline layer of gallium aluminum arsenide and an active layer of polycrystalline gallium arsenide. The presence of the intermediate layer with a wider forbidden band than that of the active layer compensates the effect on the efficiency of the limited thickness of the active layer.
A photovoltaic cell of the type comprising an ohmic bottom contact comprising a metal layer coated with a semiconductor layer, an active semiconductor layer whose thickness is approximately the same as the diffusion length of the semiconductor material, a semiconductor or metallic layer forming a rectifying junction with the active layer in such a way that the assembly can have a photovoltaic effect, further comprising between the active semiconductor layer and the ohmic bottom contact an intermediate layer which is much thinner than the active semiconductor layer and which is formed from a semiconductor compound with a forbidden band width greater than that of the active layer, the crystalline parameters of the materials of the intermediate layer and the active layer differing by 5 parts per 1000 or less.
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Photovoltaic cells having only PN heterojunction potential barriers: comprising only Group III-V materials, e.g. GaAs/AlGaAs or InP/GaInAs…
Having potential barriers: photovoltaic cells having only Schottky potential barriers
Photovoltaic [PV] energy: solar cells from Group III-V materials
Solar cells and light sensors
Term ended 29 Jan 2001 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention relates to a photovoltaic cell, which can be used in the manufacture of solar cells.
In the field of solar cells the aim is to produce equipment having a low cost, but an acceptable conversion efficiency. In practice a compromise is made between these partly contradictory requirements.
Relatively high conversion efficiencies of approximately 20% can be obtained by using as the active layer a monocrystalline material formed by a semiconductor of the III-V type, such as GaAs or InP. However, this leads to high costs and is more suitable for solar generators using optical solar flux concentration means then for standard uses.
The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein:
FIG. 1 shows an example of a prior art photovoltaic cell.
FIG. 2 is an explanatory graph.
Efficiency considerations are involved in the present invention. However, a clear distinction must be made between conversion efficiency and quantum efficiency. The former is the overall energy efficiency as referred to hereinbefore. The quantum efficiency, which is only partly involved in the total energy efficiency, is defined by the ratio between the number of charge carriers, collected by the electrodes of the photovoltaic cell and the number of photons absorbed by the semiconductor material, each of them giving rise to an electron-hole pair. It is known that among the factors reducing the quantum efficiency it is mainly necessary to measure the life time of the minority charge carriers (electrons or holes depending on whether the semiconductor material is of the p or n type) before they are collected by the electrode in question to combine in the production of electrical current.
(1) In the case of an active layer of type n mateiral, the majority carrier electrons created by the photovoltaic effect all participate in the production of current. However, the minority carrier holes partly disappear for a number of reasons:
a- their life is limited and there is an average diffusion length for these carriers which, for a material of given composition and crystalline quality, is a function of the speed of the carrier (mobility) in the medium in question and of the probability of its recombination in this medium.