CA1062799A

CA1062799A - Solar cell device having improved efficiency

Info

Publication number: CA1062799A
Application number: CA246,785A
Authority: CA
Inventors: Henry Kressel; Vikram L. Dalal
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1975-03-07
Filing date: 1976-02-27
Publication date: 1979-09-18
Also published as: DE2609051A1; GB1529631A; US3988167A; FR2303384A1; JPS5329588B2; FR2303384B1; JPS51113480A

Abstract

Inventors: Henry (NMN) Kressel Vikram Lalitchandra Dalal Title : SOLAR CELL DEVICE HAVING
IMPROVED EFFICIENCY

Abstract A body of semiconductor material in a solar cell device has a means for collecting electron-hole pairs with an incident surface through which solar radiation enters.
The collecting means can be a P N junction between two regions of opposite conductivity of the semiconductor body, or a partially transparent metallic film on the semiconductor body providing a metal to semiconductor material surface barrier rectifying junction. On a surface opposite the incident surface of the collecting means is a non-continuous oxide layer. The oxide layer is non-continuous because of openings extending through the oxide layer to the opposite surface. The openings are distributed across the opposite surface. In the openings at the opposite surface and on the oxide layer is a reflecting contact which functions both as an electrical contact and as a reflector to solar radiation in the semiconductor body.

Description

RCA 68,473 ; ~ID62799 1 The present invention relates to solar cells and more particularly to solar cells which provide increased absorption of solar radiation.
A major problem in the field of solar energy col-lection is the maximization of collection of weakly absorbed solar radiation. Solar radiation comprises radiation of both ~1 short and long wavelengths. The absorption coefficient of a '1 semiconductor material depends on the forbidden bandgap widths of the particular semiconductor material. Usually for the semiconductor materials, used in the active region of a solar ' cell, absorption of the larger wavelength portion of the 1 solar spectrum will be weaker than the short wavelength por-`I
' tion. To adjust for this weak absorption of long wavelength solar radiation it was necessary to make the semiconductor material sufficiently thick to assure absorption. Of course, / increasing the thickness of the semiconductor material used ; in the solar cell increases the cost.
'~f ~ Another problem encountered in solar,cells is having ~, ~ electrical contacts on the solar cell which do not interfere `'~ 20 with solar radiation incident onto the cell. Solar radiation , , ~ ' falling,onto a contact will probably be reflected away ~rom ~ :
'~ , ~ ,' t~he cell, lower1ng the solar céll's collection,efficiency. '' 1~ ; ~ ,While lt is 1mportant~to~prevent the loss of' solar radiation ~ -, ~ ~ co1lection~it is also important to have electrical contacts~

2S on the solar cell which are conveniently~located for the .. ~ . : . . ~ , current ~enerated anywhere in the cells' àctive region. If an e1ectrica1,contaot lS only around the periphery of a s~olar' ~- ceIl it will not interfere with solar radiation incident onto ' ' the~c,ell, but current~generated within the solar ceLl will -, ~ 30 h~ve to tr~vt1 a grenter distan~e to the co~ntact than current ~ ;

.1 - . .

RCA 68,473 1 generated at the cells' periphery. The farther current must travel through the semiconductor material to the contact, the larger the resistance it will encounter, and thus the lower the power conversion efficiency.
1 5 Therefore, it would be most desirable in the field I of solar cells to provide (1) maximization of solar radiation collection without the cost of thick active regions, and (2) electrical contacts not interfering with incident solar ra-diation but yet are conveniently located to current genera-ted anywhere in the active region.
' I . '.
A solar cell device having a body of semiconductor material including means for collecting minority carriers i¦ generated by the absorption of solar radiation in a semi-lS conductor material, with an inc:ident surface on the collect-ing means througb which radiation enters the body. On a ~ surface of the device opposite the incident surface is a non-¦ continuous ox1de layer, having openings therethrough to the ¦i opposite surface in the form of a pattern. A reflecting con-~-1 - -` 20 tact is on the oxide layer and on the opposite surface in the ¦ patterned openings 1 . . .
. FIGURE 1 is a cross~sectiQnal view of a first em-~` . - -bodiment of the solar cell device of the present invention.
.
. ~ : 25- ~ ~FIGURE 2 is a pl~an view of~the patterned contact and first oxide~layer of FIGURE 1. ~ i I

~1 FIGURE~3 is a cross-sectional view of a second em-bodiment ot the sDlar cell device of the present invention. . :-. ~ ' - ' . ': '. . .
. . . ~ , :
~

- , . RCA 68,473 ~6Z799 Referring to ~IG~RE 1, a first embodiment of the : solar cell device of the present invention is designated as : 10. The solar cell. device 10 includes a body of semiconductor material 12, such as silicon, having a first region 14 of P-type conductivity and on the first region 14 a second re-, gion 16 of N-type conductivity, with a P-N junction 18 there-between. The body 12 is the active region of the solar cell ' device 10.

- 10 ~ Opposite the PN junction 18 the second region 16 has .: .
~, ~ ' an incident surface 20, which is the surface at which solar radiation enters the semiconductor body 12. On the incident ~, surface 20 is a first non-continuous oxide layer 22 o-f an oxide materiaI transparent to solar radiation, such as sili-~,,, . 15 con dioxide. T,he first oxide layer 22 is non-continuous in , -that it has a plurality oi openings 24 extending there-through to the incident surface 20. The openings 24 are . arranged in a pattern across the entire incident sur~ace 2Q.
' The~pattern~of t`he openings is preferred as a periodic pattern,~ -.`.~i" ~ :~ 20:'~'suah:ag a:grid~pattern., As shown in FIGURE 29 the first oxide layer 22 is in the form of a checker board pattern as a~resul~of th~grid,pa't-terned openings 24 wherelrl one set of spaced paràllel openings.24 intèresect another set o~
spnced~, parnllel~openlngs 24 nt an~angle of 90 degrees, 25, However, other~pat.terns~-of openlngs can~be~used to provide '~-the~non-aontinuous ,ox1de layer 2a-. The open~ngs 24 hav'e a very,n~arrow width, W~. The f`irst oxide layer Z2 has a sur-face 23,~opposite the incid~nt surface 20.
The,~'irs~t re~ion~14 has a surface'26 opposite the '' .

'. : , ~ ` '':

RCA 68,473 3L~6Z799 1 inciden-t surface 20. On the opposite surface 26 is a second non-continuous oxide layer 28, having openings 30 there-through to the opposite surface 26. The openings 30 are in a grid pattern similar to the grid pattern of the openings 24 in the oxide lnyer 22 so that the second oxide layer 28 is also in a checker board pattern. O~enings 30 like openings 24 are also of a very narrow width, W. The second oxide layer 28 is of an oxide material such as silicon dioxide.
A contact 32 is in the openings 24 and on the inci-dent surface 20, and e~tends only minutely onto the surface 23 of the first oxide layer 22. Consequently, the contact 32 will assume the shape of the openings 24, forming a grid pattern. The contact 32 is of metallic materials having good electrical properties, such as gold and chromium.
Usually, the contact 32 consists of a layer of chromium in contact with the incident surface 20 of the second region 16 .' and a gold layer on the chromium layer. The chromium layer acts as a wetting agent to assure good adherence ~f the con-tact 32 to the second region 16. Further, because the con-j. . - : , , 20 tact 32 exte~nds only minutely onto the surface 23, the '~ ~ contact 3a will prevent only a small amount of solar radi- :

~ ation from falling onto~the incident surface 2U.
; . , ~: . .~ A reflecting contact 34 is on the opposite surface : . : , ,:
! 26 in the openings 30, and`on the second oxide layer 28.
Thnt portion of the reflecting contact 34 in the openings 30 will assume the shape of the openings 30, typicalLy forming ,~ a grid pattern. The reflecting contact 34 is of metallic materiàls hnving both good electrical properties and good solar rndiation reflective properties, such as gold and chromium. Typically, the reflecting contact 34 wlil consist 5~ ~ ~ ~

., ' ' ' ' ' .
., ' , ~:

RCA 68,473 ~L~62799 1 of a layer of chromium on both the oxide layer 28 and the first region 14 at the openings 30, with a gold layer on the chromium layer. The chromium layer acts as a wetting agent to bring about good adhesion of the reflecting contact 34.
In the operation of the solar cell device 10 of the present invention, solar radiation designated by the arrows - ., , 40, first falls on the device 10 at the surface 23. The radiation passes through the first oxide layer 22 and into the semiconductor body 12. If the solar radiation passing ~1. 1O through the semiconductor body 12 is absorbed by the body 12 1~1 an electron-hole pair is created at the point of absorption.
~¦ Electron carriers which are created in a P-type region, such : as the first region 14, and hole carriers which are created in an N-type region, such as the second region 16, are term-ed;minarity carriers in these respective regions. In order . to have a generation of current within the semiconductor , body 12, the mlnority cnrriers must reach the PN junction 18.
.~ ~ ~ The di~fusion length of a minority carrier is the aYerage .distance it can travel before it recombines. Therefore, the : .:

`I 2n ~ thickness of both the first and second regions 14 and 16 are ~ :-¦ I typically no thicker than the minority carrier diffus~ion -¦ ~ : length for the particular semiconductor material of the semi-; :condoctor body~12. ~
: ~ - : .. The .longer~the wavelength of the sola-r radiation the ~:
:~ 2S wen~ker wlll;be the~solar radi~tion absorption by the semi- .
~1 - . conductor milte~ial of the body 12. That is to say, the so:lar radintion which is of a longer wavelength, npproximately 1 . micron or greater~;for silicon, will have to travel further , . . - . . ..
.¦ ~ through a body of semiconductor material to be~absorbed, than ¦ ; 30 does solar radlation o.f a shorter wavelength. ~ .

. :

.

~ ~CA 68,473 ~C~62~799 .
1 The reflecting contact 34 is responsible for in- -.
creasing the absorption of solar radiation in the solar cell ..
device lO. Solar radiation which is not absorbed in either I the first reglon 14 or second region 16 passes through the - 5 second oxide layer 28, which is transparent to solar radi-ation, but upon striking the reflecting contact 34 it is j reflected back into the semiconductor body 12 for a second ¦ pass. Thus, one of the functions of the reflecting contact ¦~ 34 is to reflect unabsorbed solar radiation back into the body 12 thereby improving the possibility for absorption.

. The second oxide layer 28 indirectly is responsibl~
for increasing the device lO absorpticn of solar radiation.
If the ref'lecting contact 34 were in intimate contact with : . the first region 14.inste~d of the second oxlde layer 28, in .'`! 15 the deposition of the reflecting contact 34 a thin alloy ; layer would form between the reflecting contact and the semi- :
~, . conductor material o~ the first region 14. Such an alloy .
~ layer wiil asually itself absorb solar radiation incident :` '~ onto it, resulting ln :the loss of solar radiation which will-~.! : ~ : 20 not be absorbed within the semiconductor material of body 12. ~ :
.~ : . Wherever the slecond oxide layer 2~ is an intermediate b.etween ~a ~ the first region 14 and the reflecting~contact 34, no alloy ~ .
RYer~ absorbing~solar radiation, is formed. Therefore, the al;loy .layer:.wlll only be formed where reflecting contact 34 . ;~.:
~ is in openlngs 30 nnd on the first region 14, which:accou~nts for: onlyia small portion of the first region 14 at the~oppo- .
site.sur~ace~26. ~ :
Solar radiat1on not absorbed ln body 12 dur1ng the ~ ~:

~ first pnss m~y be absorbed durlng the second pas~s, that IS, 1- . 30 : - ~ ..
:`
.' ~ -7- : .
, .. , ` , ,1 RCA 68,~73 2i~99 1 after it has been reflected off the reflecting contact 34.
The incident surface 20 is a boundary between two different materials, i. e., the oxide layer 22 and second region 16, '~ and according to principles of optics well known in the art, it may be partially reflecting to both solar radiation 40 traveling from the atmosphere and unabsorbed solar radiation in the body 12. If during the second pass through the body 12 the solar radiation is not absorbed, some of the un-~¦ absorbed solar radiation incident onto the first oxide layer 22, at the incident surface 20 may again be reflected back into the body 12. Thus, for some unabsorbed solar radiation ` more than two passes throu~h the body 12, is possible in the ; solar cell device 10.
As is well known in the art, surface recombination lS velocity at the free surface of a semiconductor body is high.
In order to lower the surface recombination velocity at both ` the incident surface 20 and opposite surface 26, both first and second oxide layers 22 and 28 can be provided to funotion as passiva~tion layers, such as by being thermally grown Onto the sùrfaees 20 and 26. With the surface recombination~
velocity reduced at both incident surface 20 and opposite surface 26, the possibility of minority carriers recombining at the surfaces 20 and 26 is reduced, thereby increasing . . ~ . .
" ~ - solar cell device 10 efficiency.

Both contact 32 and reflecting contact 34 function as electrical contacts to the second region 16 and the first ~ re~ion 14, respectively. As previously stated, the openings ; ; ~ 24~nnd 30 are o~n very narrow width~l W, and the contact-32 and~a portion~o~ reflectini~ contnct 34 on the~opposite sur- ~ -face 26 assumes the shape of the openings 24 and 30, respect-:
- ~ : -8-. . , .` ' ~ ' ' :

RCA 68,473 . .
~L~62799 1 ively. Since the contact 32 and a portion of the reflecting contact 34 are patterned so as to be distributed across -the incident surface 20 and the opposite surface 26, respectively, , the current generated in the body 12 is always close to a 1 5 portion of the contact so as to encounter less electrical .~ resistance in traveling out of the body 12. In addition to providing a convenient electrical path for current generated 1 in body 12, the patterned shape of the contact 32 allows most ; ¦ of the llght incident on surface 23 to reach the semiconductor .1 10 material of body 12, while the shape of the reflecting con-! ~ tact 34 allows it to reflect back into body 12 most of the . unabsorbed solar radiation incident onto it.
. The exact dimension oiE the width, W, of each grid in the grid pattern of contact 32 and reflecting contact 34, and ~ 15 :their spacing apart, is a function O:e the resistivity of the :~ semiconductor materlal of the body 12. The higher the resist-. ivity of the semiconductor material, the wider will be the ::
.. ~ wi:dth, W, and the~closer the spacing apart, in order to pro- ; :
vide ~;curre:nt pnth of low resistance. Typically, for silicon `20 ~the widthj W,~of each grid in the grid pattern of contact 32 ~1 ` and reflèctlng contact 34, will be approximàtely 2 mils, with ~ :
: ~ each grld~spaced~-about lO0 mils apart from other grlds ex~
. . ~ tending in the~:8ame dlrection. : ~ . -n the:f~nbrication of the solar cell device 10 of ~ -the present invention, a i`lnt semiconductor wa~er comprising ~ he;first~and second regions 14 nnd l6 can be formed by~state of the:art epitaxy or diffusio~ techniques. The thickness~of ` the:first~reglon 14 ls adJusted to approximate the diffusion ; . length of-an electron carrier in the:semiconductor material ~of the flr~t réglon 14, while the thickness of the~second .~ ~ ~ 9~ `

.` : : ' ~ RCA 68,473 ~2799 1 region 16 is adjusted to approximate the diffusion length of a hole carrier in the semiconductor material of the second region 16. After the flat wafer is formed an oxide layer is thermally grown on the wafer. The oxide layer on the edges - - 5 of.the flat wafer are than etched off so that only the first and second oxide layers 22 and 34 remain. Next, the openings ' 24 and 30 are formed into the oxide layers by utilizing state 1~ of the nrt masking and photoresist techniques. Then reflect- I
1 ing contact 34 is formed by first depositing, by vacuum evap-1 10 oration, a lOOA layer of chromium onto the first region 14 at ` 1 .
the openings 30, and onto the second oxide layer 28. Secondly ~ a layer of gold is deposited by vacuum evaporation onto the .¦ chromium layer, filling in the openings 30. Contact 32 is : formed by first depositing a chlromium and then gold layer on .
: . 15 the second region 16 at openin~;s 24, and onto the first oxide i~ layer 22, as was done to form the reflecting contact 34.
¦ Finally, by Using State of the art photoresist technology the ¦ chromium and gold layers deposited on the first oxide layer

2~ are etched away so that only contact 32, occupying the 2Q openings 24, remains.

; ~ ~ ~ In tbe description of the solar cell device 10 the ~ first region 14 is of P-type conductivity and the second , i - . ~ : :
reglon:l6 is of N-type.eonductivity, but it 1S anticipated by the present~invention that the conductivities of the 125 ~ flrs;t;and second~regions can be opposlte fromlwhat has been described.. It is also ~nticlpated by the pres~ent invention ~ thnt the openlngs~24 and 30 need not be in a grid~pattern. .
:j ~ The openings 2~4~and 30, and consequ~ntly.contact 32 and the - portion of reflecting contact 34 on the first region 14, can ~ ~ ~ 30 - ~
., ' ' - 1 0- , :', ` . ' ;' ~ ~ ', , : ,:

l ~ , , , :
;l ' ' : . :

RCA 68,473 ~L06;~799 :
1 be in any pattern that is distributed across tbe surfaces 20 and 26, such as concentric circles radiating out of the center of the device 10 and connected by a common contact.
The pattern of contact 32 and reflecting contact 34 may be periodic across the surfaces 20 and 26.
. j . :
It is desirable in the solar cell device 10 that the ' pattern ~f the contact 32 and the reflecting contact 34 be I aligned, so as to minimize losses of solar radiation that I could possibly be absorbed. Contact 32 prevents solar radiation which first strikes it from traveling into the I semiconductor body 12. Unabsorbed solar radiation in the '~
'I body 12 incident onto the patterned portion of reflecting l contact layer 34 at the opposite surface 26 will very possibly .1 . .
,l not be re~lected back into the body 12. As mentioned pre-::~
' 15 viously, a metal on,a semiconductor material may form an alloy interface, which itself nbsorbs incident radiation.
Thus, even though solar radiation first striking the contact 32 is prevented from entering the body 12, this loss is mini-mized by alignlng the patterns, since the possibility of un-~
~' 20 absorbed radiation being reflected back into body 12 is very ' `~ poor i~ such radiation is incident onto the patterned portion "1 ~ ' of reflecting contact 34. In essence, alignment of the i pa~tterns minimizes that~area of the device 10, as viewed by ncident solar radiation, having undesirable qualities. ' ~25 ; ~ While lt;is implicit from the description~of the ,~
contnct'p:lttern previo~!sly given thnt both contact 32 and reflecting contact~34 be of the snme pattern, it is antici-' ' pated~by~the present invention that they need not be of the , ' `, ; same pattern. ~ , ~,l 30 RCA 68,473 ~L062799 1 Referring to EIGURE 3, a second embodiment of the solar cell device of the present invention ls designated as 110. In the solar cell device 110 a metallic film 111 is on a surface of a semiconductor body 114, having an interface 115 therebetween. The metallic film 111 has a surface 117 oppo-site the interface 115. Surface 117 is the surface at which . solar radiation is incident onto the metallic film 111. The semiconductor body 114 is the active region of the device 110.
The metallic film 111 is thin so as to be partially trans-parent to solar radiation 1409 and the semiconductor body 114 is typically of a semiconductor material such as silicon, of N-type conductivity. Typically, the metallic film 111 is of ~ a metal which forms a surface barrier junction, such as gold '~ or platinum.
' 15 On an opposite surface 1'26 of the sem1conductor body 114, opposite the interface 115, :Ls a non-continuous oxide '~' layer 128, having openings 130 the same as the first oxide layer 28 and~openings 30 of the first embodiment. On the 'oxide layer ~128 and on the semi~onductor body 114 at the open-` ' '20 ings 130 is a re:'flective contact 134, the same as the reflec-s '` tive contact'34 in the firs't embodiment o~ the present inven-t~ion. The patt'ern of the openings 130, and thus, that portion ~ ~-of:the refleo~tive contact 134 in contact with the semiconduc-tor~body 114~can~be i~n any pàttern that is distributed across and in cont~act with~the semlconductor body 114, as was described in~the`solar~cell devicè lV.
elA~ known in the~semiconductor~nrtj is that a~metal~
~ lm can~ be provlded on a semlconductor body resulting ln a - - metal tv semiconductor material surf~ce barrier recti~ying ~ :

.

... .
, ~ . . :
.

, ,,, , , , , . , .,.::, . RCA 68,473 ~. .

6279g .
1 junction. Such a barrier at tlle interface of a metal film and semiconductor body is termed a Schottky barrier.
Typically, the semiconductor body is of a semiconductor material such as silicon, germanium or a group III-V semi-conductor compound. It is intended in the second embodimen$
I of the present invention.to have a Schottky barrier at the interface 115 and extendin~ into the semiconductor body 114. .
: In the operation of the second embodiment of the present invention some of the solar radiation striking the :
I ~: lO incident surface 117 will pass through the partially trans~
. : parent metallic film 111 and travel into the semiconductor `~1 body 114. While in the semiconcluctor body 114, some o~ the .1 solar radiation will be absorbecl, forming electron-hole pairs.
~I Depending on the conductivity of the semiconductor body 114, .. l l5 holes or electrons with sufficient energy, traveling toward :~
the Schottky barrier, will go over the barrier and generate a : current.
. .
~ ;I Solar radiation which has not been absorbed in the : ~ semiconductor body 114 will strike the re~lecting contact 134 ~0~ and be reflected back into the semiconductor body 114. -If in ¦ ~ bein~ reflected:back i~to the semiconductor body~114 the -.

. ~ solar radia~:tion is still not absorbed, it wil:l strike the.
~......... - , .: , - :

~ partial~ly transparent metallic film 111. Since metallic film :: . ,.
.~ . ~ 111 is only partially transparent to solar radiation, only a 1~ 1 `25~; portion~of the so:lar~radiation striking lt will~be ~reflected bnck into the semiconduotor body 114. ~Thus, there 1s the ~i :... posslibil~ty~`of~u~nabsorbed solar radlation making more than~ : b two passes throu~h t~e semiconductor:body 114 of the solar .~ :

cell device 110:.
~30 ~: -13-.
, : :

- RCA 68,473 ~ 36Z799 i The reflecting contact 134 provides an electrical contact which is distributed across the semiconductor body 114 to provide generated current with a low resistive path out of the semiconductor body 114. Since the partially trans-parent metallic film 111 is continuous over the semiconductor body 114 it may provide even a lower resistance path to gene-l rated current than the reflecting contact 134, dependin~ on I the resistivity of the metal used and thickness of the par-tially metallic film 111.
., .
In the fabrication of the solar cell device 110 a wafer of a semiconductor material such as silicon is cut from I an ingot of semiconductor material. After cleaning, lapping : and polishing the wafer to form the semlconductor body 114, I a thin metallic layer of material such as gold or platinum . ~. 15 is deposited on a surface of the semiconductor body 114 by .: vacuum eVapOratlOII to form the partially transparent metallic I ~iLlm 111. The metallic film ll:L is on the order of about : - 100 A in tbickness to assure it will be partially transparent :. ~ to solar radiation. Fabrication of the solar cell device ~ ~ 20. 110 is complèted b~ depositing the oxide layer 128 and re~

"`I ~ flecting cont~ac~t 134~on a surface of tbe semiconductor body . I : 114 opposite the partially transparent metallic film 111, as ¦ I dlscussed in the fabricatlon of the first embodiment of the .y ~ present :invention.

., 1 25 The solnr cell devi.ces 10 and 110 offers the ad~

vantqge ol at least a second pass for unabsorb0d solar radi-. ~ation through the active region, and electrical contacts .
.. :~ ~ which provide the.current generated in the active region with ::

. ~ a low resistive path out of the active region.
:'j 30 ~:

' ¦ !
~' 1 : ::".
,~ , , .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A solar cell device comprising:
a body of semiconductor material having means for collecting minority carriers generated by the absorption of solar radiation in the body, an incident surface on the collecting means, through which radiation enters the collecting means, a non-continuous oxide layer on a surface of the collecting means opposite the incident surface, the oxide layer having openings therethrough to the opposite surface, the openings being in the form of a pattern distributed across the opposite surface, a reflecting contact on the oxide layer and on the opposite surface in the patterned openings, a non-continuous oxide layer on the incident surface, the oxide layer having openings therethrough to the incident surface, the openings being in the form of a pattern, the patterned openings of the oxide layers on the opposite surface and the incident surface being of the same pattern and in alignment with each other, and a contact on the incident surface in the patterned openings.

2. The solar cell device in accordance with claim 1 wherein the collecting means of the body of a semi-conductor material comprises a first region of one conduc-tivity type, a second region of an opposite conductivity type on the first region, with a PN junction therebetween.

3. The solar cell device in accordance with claim 1 wherein the pattern of the openings in both oxide layers is in the shape of a grid.

4. The solar cell device in accordance with claim 3 wherein the pattern of the openings in both oxide layers is periodic in shape.

5. The solar cell device in accordance with claim 4 wherein the first region is of a P-type conductivity and the second region is of an N-type conductivity.

6. The solar cell device in accordance with claim 5 wherein the oxide layers are of silicon dioxide.

7. The solar cell device in accordance with claim 6 wherein both the contact and reflecting contact are of both chromium and gold.