U.S. patent application number 13/673992 was filed with the patent office on 2013-11-21 for seebeck solar cell.
The applicant listed for this patent is Joseph A. Micallef. Invention is credited to Joseph A. Micallef.
Application Number | 20130306125 13/673992 |
Document ID | / |
Family ID | 39149842 |
Filed Date | 2013-11-21 |
United States Patent
Application |
20130306125 |
Kind Code |
A1 |
Micallef; Joseph A. |
November 21, 2013 |
Seebeck Solar Cell
Abstract
A Seebeck solar cell device is disclosed, combining both
photovoltaic and thermoelectric techniques. The device may be
formed using, for example, a conventional photovoltaic cell formed
from a doped silicon wafer. The material used to form conductors to
the front and rear regions of the cell are chosen for their
thermoelectric characteristics, including the sign, or polarity, of
their Seebeck coefficients. The distal portion of each conductor is
insulated from the solar and waste heat and, in some embodiments,
is also coupled to a cooling mechanism. Multiple such devices can
be connected in series or parallel.
Inventors: |
Micallef; Joseph A.; (Chevy
Chase, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Micallef; Joseph A. |
Chevy Chase |
MD |
US |
|
|
Family ID: |
39149842 |
Appl. No.: |
13/673992 |
Filed: |
November 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11469885 |
Sep 4, 2006 |
8334450 |
|
|
13673992 |
|
|
|
|
Current U.S.
Class: |
136/206 ;
136/201; 438/54 |
Current CPC
Class: |
H02S 10/10 20141201;
H01L 31/18 20130101; Y02E 10/50 20130101; H01L 35/32 20130101 |
Class at
Publication: |
136/206 ; 438/54;
136/201 |
International
Class: |
H01L 31/058 20060101
H01L031/058; H01L 31/18 20060101 H01L031/18 |
Claims
1. A photoactive apparatus, comprising: an n-type region and a
p-type region, a first conductor formed of a first thermoelectric
material and coupled to said n-type region, said first
thermoelectric material having a thermoelectric coefficient of a
first polarity, and a second conductor formed of a second
thermoelectric material and coupled to said p-type region, said
second thermoelectric material having a thermoelectric coefficient
of a second polarity.
2. The photoactive apparatus of claim 1, wherein one of said n-type
region and said p-type is above the other.
3. The photoactive apparatus of claim 1, wherein neither of said
n-type region and said p-type is above the other.
4. The photoactive apparatus of claim 1, wherein said first
conductor is further formed of a third thermoelectric material
having a thermoelectric coefficient of said first polarity.
5. The photoactive apparatus of claim 4, wherein said second
conductor is further formed of a fourth thermoelectric material
having a thermoelectric coefficient of said second polarity.
6. The photoactive apparatus of claim 1, wherein at least one of
said n-type region and said p-type region is formed of an organic
polymer.
7. The photoactive apparatus of claim 1, wherein at least one of
said n-type region and said p-type region is formed using quantum
dots.
8. An apparatus, comprising: a first photoactive cell formed of a
first region of a first type and a second region of a second type,
a first conductor formed of a first thermoelectric material and
coupled to said first region, said first thermoelectric material
having a thermoelectric coefficient of a first polarity, and a
second conductor formed of a second thermoelectric material and
coupled to said second region, said second thermoelectric material
having a thermoelectric coefficient of a second polarity.
9. The apparatus of claim 8, further comprising: a second
photoactive cell formed of a first region of a first type and a
second region of a second type and electrically coupled to said
first photoactive cell.
10. The apparatus of claim 9 wherein said first and second
photoactive cells are electrically coupled in series.
11. The apparatus of claim 9 wherein said first and second
photoactive cells are electrically coupled in parallel.
12. A method of fabricating a photoactive apparatus, comprising the
steps of: forming a photoactive cell having an n-type region and a
p-type region; forming a first conductor for coupling to said
n-type region, said first conductor formed of a first
thermoelectric material having a thermoelectric coefficient of a
first polarity; forming a second conductor for coupling to said
p-type region, said second conductor formed of a second
thermoelectric material having a thermoelectric coefficient of a
second polarity.
Description
[0001] This is a continuation of application Ser. No. 11/469,885
filed Sep. 4, 2006.
BACKGROUND OF THE INVENTION
[0002] Alternative energy sources are being given renewed attention
due to the high price of oil, environmental concerns associated
with hydrocarbon-based technologies and political instability in
oil producing areas of the world. One such potential source of
energy is solar power. Another is thermoelectric power.
[0003] Solar energy, of course, has been the subject of study and
of commercial exploitation for some time. A great deal of time and
effort has been spent researching how best to convert the sun's
energy into power usable in modern society. While many different
techniques have been devised, photovoltaic cells are by far the
most common and commercially successful. The operation of a
photovoltaic cell is well understood. When the cell is exposed to
solar radiation it absorbs photons of a certain energy. The photons
transfer energy to electrons in the crystal lattice of the silicon.
The transferred energy "excites" the electrons into the conduction
band, creating the possibility of a flow of charge carriers through
electrical contacts coupled to the cell. For purposes of this
application, a photovoltaic cell is a device capable of converting
photons from the sun into electricity by the generation of charge
carriers in a light-absorbing material.
[0004] But photovoltaic cells suffer from significant limitations
of efficiency. One reason for the inefficiency is the inability of
low energy photons to move valence band electrons to the conduction
band in the conventional materials used in modern photovoltaic
cells. Another related reason is the conversion of much of the
solar energy to which the cells are exposed to waste heat. And
while research continues into better materials capable of
converting more of the available solar energy to electricity, to
date only minimal progress has been made in that direction. Thus, a
need exists for methods and materials that increase the efficiency
of photovoltaic cells.
[0005] Another alternative energy source that is only recently
coming back into vogue is thermoelectric energy. Almost two
centuries ago it was discovered that a temperature gradient in
certain materials can create a voltage within the material. The
voltage is caused by the diffusion of electrons from a hot region
to a cold region, or vice versa. This is the so-called
thermoelectric, or Seebeck, effect. During the middle part of the
twentieth century the Seebeck Effect was the subject of some
research. However, once it was determined that conventional
materials possessed only relatively low "figures of merit"--and
therefore could create only very small thermoelectric
voltages--interest in the phenomenon diminished.
[0006] The figure of merit, usually designated "Z", is a quantity
describing the thermoelectric characteristics of a certain material
as a function of temperature. It is the product of three quantities
of a particular material--the electrical conductivity, the inverse
of the thermal conductivity and the "Seebeck
coefficient"--multiplied by the temperature. It is important to
recognize for purposes of the present invention that the Seebeck
coefficient can be either positive or negative. The sign, or
polarity, of the Seebeck coefficient indicates the "direction" of
the voltage created by a temperature gradient, that is, whether the
hot side is positive or negative.
[0007] The prior art recognized that for conventional materials the
non-temperature quantities that comprise the figure of merit for
any particular material vary with each other so that it was very
rare to identify a material with a figure of merit much greater
than 1. Interest in using the thermoelectric effect to generate
power therefore diminished. And while more recently interest in
developing new materials having higher figures of merit has
increased, the successful exploitation of the Seebeck effect in
power generation has been very limited. What is required,
therefore, is a use of thermoelectric technology that more
successfully generates energy.
[0008] Combinations of photovoltaic and thermoelectric technology
have been attempted in the past, with little or no success. It
appears that prior attempts to combine both technologies have not
created sufficient power to justify the added expense such systems
required, or perhaps simply did not work. In any event, it appears
that the art has lost interest in such combinations, and instead
appears to be focused on the development of thermoelectric
generators outright. What is needed, therefore, is a more efficient
and powerful combination of solar and thermoelectric
technology.
SUMMARY OF THE INVENTION
[0009] The present invention fulfills each of these needs.
[0010] A Seebeck solar cell device is disclosed, combining both
photovoltaic and thermoelectric techniques in an efficient and
powerful way. The device may be formed using, for example, a
conventional photovoltaic cell formed from a doped silicon wafer.
The material used to form conductors (e.g., contacts or leads) to
the front and rear regions of the cell are chosen for their
thermoelectric characteristics, including the sign, or polarity, of
their Seebeck coefficients. More specifically, a first material
having a negative Seebeck coefficient is used to form a conductor
to the n-type region of the cell and a second material having a
positive Seebeck coefficient is used to form a conductor to the
p-type region of the cell. Electrical current is produced not only
from the conventional photovoltaic processes, but also from the
temperature gradient produced in the conductors due to exposure to
solar radiation and to waste heat generated in the photovoltaic
cell itself. It is preferred that the distal portion of each
conductor is insulated from the solar and waste heat and, in some
embodiments, is also coupled to a means for cooling, thereby
increasing the temperature gradient. Multiple such devices can be
connected in series or parallel.
DESCRIPTION OF THE FIGURES
[0011] FIG. 1 depicts an exemplary solar cell in accordance with
the present invention.
[0012] FIG. 2 depicts several exemplary solar cells in accordance
with the present invention and connected in a series
configuration.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to FIG. 1, an exemplary device 10 in accordance
with the present invention is depicted. In that example a
conventional photovoltaic cell is formed by diffusing an n-type
dopant into one region 14 of a p-type wafer 16. Region 14 will be
referred to here as the "front" of the cell because in this example
that is the region most directly exposed to solar radiation. Those
of ordinary skill in the art will understand that the commercial
manufacture of such a cell will require various additional
structures, steps and details not described here, such as
deposition of an antireflective coating, sintering, a tempered
glass front cover and polymer encapsulation. All of these are
well-known to the art and therefore are not described in further
detail.
[0014] Front contact 20 is formed in the upper/front (n-type)
region and connected to a first electrical lead 21, having lead end
22. The front contact and first lead are formed in a conventional
manner, well-known in the art. In particular, front contact 20 may
be formed from several buried contacts positioned in a grid-like
manner (not shown) across the face of region 14 and electrically
connected together.
[0015] In this embodiment of the invention the front contact and
first electrical lead are both formed from the same material and
that material possesses a negative Seebeck coefficient. Moreover,
it is preferable that the material have as high a figure of merit
as possible. Nickel is one example of a material possessing a
negative Seebeck coefficient, and is also a material which has been
used for the formation of front contacts in photovoltaic cells.
Bismuth telluride is another example of a suitable material that
has been used in that manner in the art, and one that has a higher
figure of merit than nickel. Silicon germanium and other telluride
compounds are also suitable.
[0016] A full area rear contact 23 is formed along the rear side
(p-type) of the wafer and connected to a second electrical lead 24,
having a rear lead end 25. The rear contacts and second lead are
formed in a conventional manner, well-known in the art. In this
embodiment of the invention the rear contact and second electrical
lead are formed from the same material and that material possesses
a positive Seebeck coefficient. Boron carbide is one example of
such a material. Copper and molybdenum are other examples.
[0017] The distal portions of the leads 21 and 24 are placed in
thermal contact with a cooling mechanism, such as a heat sink or
heat pipe, and there-from electrically connected to a load (not
shown). The leads are electrically insulated from the cooling
mechanism by a thermally conductive adhesive layer 32, such as a
tape or resin as is conventional. Additional insulating layer 35 is
formed to electrically insulate lead 21 from the p-regions of the
wafer 16. Insulating layer 36 is formed to thermally and
electrically insulate the rear contact from the cooling mechanism
and to electrically insulate the leads from each other. Insulating
layers 37 are formed to thermally and electrically insulate the
interior portions of cell 10 from the external world. These
insulating layers are formed using conventional techniques and
materials.
[0018] Front contact 20 is exposed to the sun and therefore in
operation will increase in temperature. Lead end 22 and the
portions of first electrical lead 21 near it, however, are in
thermal contact with cooling mechanism 30 and hidden from the sun's
energy by insulating material 37. In operation, therefore, a
temperature difference is created between contact 20 and lead end
22, thereby creating a diffusion of charge carriers due to the
thermoelectric, or Seebeck, effect. Because contact 20 and lead 21
are formed of a material having a negative Seebeck coefficient, the
flow of electrons within those structures will be from the "hot"
end (contact 20) to the "cold" end (lead end 22), which is the same
direction as the flow of electrons from the conduction band of
n-region 14 pursuant to the conventional photovoltaic
processes.
[0019] Similarly, rear contact 23 is thermally insulated from the
cooling mechanism 30, thereby trapping waste heat from the wafer in
that contact and causing the temperature of the contact to rise.
That rise in temperature will assist in creating a temperature
differential between the contact 23 and the lead end 24, which is
not in direct thermal contact with wafer 16 but is in thermal
contact with cooling mechanism 30. This causes a difference in
temperature between contact 23 and lead end 25 (and the portions of
lead 24 near lead end 25). Because contact 23 and lead 24 are
formed of a material having a positive Seebeck coefficient, the
flow of electrons within those structures will be from the cold end
(lead end 25) to the hot end (contact 23), which is the same
direction as the flow of electrons into wafer 16 pursuant to the
conventional photovoltaic processes.
[0020] It should be noted that the device described above and
depicted in FIG. 1 is merely an example offered to explain the
invention. Many variations are possible within the scope of the
invention defined in the claims. One such variation would embrace a
photovoltaic cell formed by diffusing a p-type dopant into one
region of an n-type wafer. In that case, however, the materials
selected for the front and rear contacts would have Seebeck
coefficients of the opposite polarity than those described with
respect to FIG. 1. Another variation would involve formation of the
conductors coupled to either the anode or cathode portion of the
cell from more than one material. For example, the contact 20 might
be formed of a first material and lead 21 from a second. In that
case, however, the two materials must each have a Seebeck
coefficient of the same polarity.
[0021] The invention can be applied to any of a number of different
types of photovoltaic cells, including first, second and third
generation cells. This includes, but is not limited to,
conventional p-n junction cells of various materials including
doped silicon or gallium arsenide devices, multi-layer cells or
configurations employing special dyes, organic polymers or quantum
dots.
[0022] Referring now to FIG. 2, the invention can be employed in a
series configuration of multiple cells. FIG. 2 depicts cells 100,
200 and 300 that, in this example, are similar in structure and
operation to cell 10 of FIG. 1. Cells 100, 200 and 300 are
connected in a series configuration in that the cathode of one cell
is electrically connected to the anode of its neighboring cell.
Thus, read lead end 125 of cell 100 is connected to front lead end
222 of cell 200. And rear lead end 225 of cell 200 is connected to
front lead end 322 of cell 300. Lead ends 122 and 325 are available
to be connected to a load (not shown).
[0023] Of course, FIG. 2 depicts three cells in this configuration
for purposes of clarity. Those of ordinary skill in the art will
recognize that other numbers of cells may be so joined. Also, note
that FIG. 2 depicts each cell 100, 200 and 300 with a separate
cooling mechanism. However, in this configuration a single cooling
mechanism across many cells may be employed.
[0024] A plurality of the solar cells of the present invention may
also be electrically connected in parallel. In this configuration
(not shown) conductors coupled to the cathode of each such cell are
electrically connected together and the conductors coupled to the
anode of each such cell are also electrically connected together.
Such electrical connection of photovoltaic cells is well known to
those of ordinary skill in the art and will therefore not be
further described.
[0025] The invention has been described by use of the examples
described above. Nothing in the specification should be interpreted
to limit the scope of the invention beyond what is recited in the
claims.
* * * * *