Photoelectrochemical cells for conversion of solar energy to electricity and methods of their manufacture

A photoelectric device is disclosed which comprises first and second layers of semiconductive material, each of a different bandgap, with a layer of dry solid polymer electrolyte disposed between the two semiconductor layers. A layer of a polymer blend of a highly conductive polymer and a solid polymer electrolyte is further interposed between the dry solid polymer electrolyte and the first semiconductor layer. A method of manufacturing such devices is also disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to photoelectric cells and methods of their 
manufacture, and more particularly to such cells employing dry, solid thin 
film polymer electrolytes and methods of their manufacture, as well as 
polymer films for use in such cells. 
2. Description of the Prior Art 
Photovoltage or the photovoltaic effect may be defined as the conversion of 
light or electromagnetic photons to electrical energy by a material. 
Becquerel in 1839 was the first to discover that a photovoltage developed 
when light was shining on an electrode in an electrolyte solution. Nearly 
half a century elapsed before this effect was observed in a solid, namely 
in selenium. Again, many years passed before successful devices such as 
the photoelectric exposure meter, were developed. Radiation is absorbed in 
the neighborhood of a potential barrier, usually a pn junction or a 
metal-semiconductor contact or junction, giving rise to separate electron 
hole pairs which create a potential. 
Photovoltaic cells have found numerous applications in electronics and 
aerospace, notably in satellites for instrument power, and powering 
communications apparatus in remote locations. 
Intensive research has been underway in the last decade to improve the 
production of these cells, e.g., (1) increasing the practical efficiency 
in order to approach the theoretical efficiency, (2) decreasing production 
costs, and (3) to find new materials and combinations. 
Interest in alternative energy sources and particularly in solar energy has 
increased because of political and economic impetus. Traditional sources 
of inexpensive energy are rapidly disappearing. Political instability, 
price/supply fixing by certain governments, and environmental concerns, 
dictate the search for new energy sources. Thus the present interest in 
solar energy. Each country has its own sunlight supply, and the United 
States has an ample supply. Ecologically, solar cells are a non-polluting 
clean source of energy. Solar energy in our forseeable future for many 
generations is limitless and non-depletable. One application of solar 
energy to which the present invention is directed is the direct conversion 
of electromagnetic radiation, particularly sunlight, to electricity. 
Two of the classical goals of any photovoltaic cell are efficiency, and 
higher output voltage. Most prior art cells have a theoretical efficiency 
of 25%. The cells of the present application approach 35%. The prior art 
voltage ranges from 0.2 to 0.5 volts per cell; the inventor's cells are 
approximately 0.625 volts. 
Further, some prior art cells require that they be oriented so that the 
incident light is perpendicular to the face of the cell. In the present 
invention, while this is desirable, it is not essential, and they may 
operate at an angle from the perpendicular. 
In the parent applications of which this forms a continuation-in-part, 
there is described in one embodiment a photovoltaic cell having a 
semiconductor layer and an adjacent polymer electrolyte. To improve the 
electrical properties at the interface, there is included a conductive 
film between the semiconductor and the adjacent solid polymer electrolyte. 
One of the objects of the present invention is to provide a conductive 
film that increases the interfacial contact area and improves the charge 
transfer characteristics between the semiconductor and polymer 
electrolyte. 
The present invention offers the possibility of ease of manufacture, 
attendant low cost, and manufacturing of large surface areas with good 
quality and at a low cost. 
The present invention is corrosion free. A reduction oxidation couple in 
water has a competing photocorrosion reaction resulting from an 
interaction between the water and semiconductors. The present invention by 
using a polymer matrix avoids photocorrosion and the attendant problems. 
An object of the present invention is to provide novel, double and multiple 
photoelectric cells for conversion of solar energy to electricity. 
Another object of the invention is to provide a method for the manufacture 
of double photoelectrochemical cells. A further object of the invention is 
to provide a half-double photoelectrochemical cell for the conversion of 
solar energy to electricity using a thin film polymer electrolyte, said 
polymer electrolyte being non-aqueous and solvent free. 
A futher object of the invention is to provide a new family of 
photoelectrochemical cells having a theoretical higher output efficiency 
and output voltage than is available from single cells. 
Another object of the invention is to provide cells which are easy to 
manufacture and are stable in operation. 
As noted in the parent applications, there is described a photovoltaic cell 
in which there is a thin film solid polymer electrolyte with a 
semiconductor adjacent thereto, and a conductive film between the solid 
polymer electrolyte and the adjacent semiconductor. An object of the 
present invention is to provide an improved conductive layer that 
increases the interfacial contact area and the charge transfer 
characteristics from the solid polymer electrolyte. 
A further object is to provide a film of a polymer blend of a highly 
conductive polymer and a solid polymer electrolyte, which can be used for 
electric cells. 
A further object of the invention is to provide a method of manufacturing 
of conductive polymer electrolytes for use in electric cells. 
These and other objects and features of the invention will be more fully 
understood from the description of the embodiments which follow, but it 
should be understood that the invention is not limited to these 
embodiments and may find application as would be obvious to a man skilled 
in the art following the teachings of this application. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, there is provided a device having 
a first layer of semiconductive material having a first band gap; and a 
second layer of semiconductive material having a different band gap; a 
layer of dry solid polymer electrolyte between said first and second 
layers; and a layer of a polymer blend of a highly conductive polymer and 
a solid polymer electrolyte between said dry solid polymer electrolyte and 
said semiconductor layer. 
According to another aspect of the invention, there is provided a method of 
manufacturing such cells. 
According to an aspect of the invention there is provided a thin film 
providing improved electric charge transfer across said film having a 
polymer blend of a highly conductive polymer and a solid polymer 
electrolyte, said blend being the major component of said film at one face 
thereof, and said dry solid polymer electrolyte being the major component 
of said film at another face thereof. Said blend of said conductive and 
electrolyte polymers is more conductive than said dry solid polymer 
electrolyte. 
According to another aspect of the invention there is provided a method of 
manufacturing such film and device.

The parent applications describe in at least one embodiment photovoltaic 
cells having a dry solid polymer electrolyte and adjacent semiconductor 
layer. This invention, in one aspect, describes an improved contact 
between said solid polymer electrolyte and semiconductor. This improved 
contact uses a polymer blend of a highly conductive polymer, e.g. 
polypyrrole, and a solid polymer electrolyte, e.g. polyethylene oxide 
complexed with potassium iodide. This blend leads to an increase in the 
interfacial contact area and an improved charge transfer characteristic 
between the electrolyte and the semiconductor. It will be appreciated that 
there may be additional intermediate layers of conductors such as platinum 
between the semiconductor and the blend. There is also described a method 
for manufacturing such a blend and the complete cell. In this application, 
FIGS. 1 through 12 and the attendant description come from the parent 
applications. FIGS. 13 and 14 and the attendant description are additional 
to this continuation-in-part application. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1 there is schematically shown the photoelectrical cell having two 
semiconductors, 1 and 2, separated by a polymer electrolyte 3. Incoming 
electromagnetic radiation, for example, sunlight, is shown by an arrow 4. 
Electrodes 5 and 6 are connected to the semiconductors 1 and 2, 
respectively. The electrodes are connected by leads to a load shown here 
as a meter 7. 
Semiconductor 1 is a thin film of cadmium sulfide, CdS, n-type, and is a 
thin film, approximately 1 micrometer thick. As shown in FIGS. 2 and 3, 
n-type CdS has a wide band gap. Semiconductor 2 is a thin film of cadmium 
telluride, CdTe, and is doped with a p-type impurity. The n-CdS is undoped 
and is balanced with more or less Cd or S. It is naturally n-type due to 
vacancies in the structure of the material and cannot be p-type. The 
resistivity can be adjusted by the manufacturing process. The CdTe is 
doped p-type with phosphorous to a concentration of 1.3.times.10.sup.16 
cm.sup.-3. P-type CdTe has a narrower band gap than that of n-type CdS as 
shown in FIGS. 2 and 3. The two semiconductors 1 and 2 face each other, 
and are in contact with and separated by the thin film polymer electrolyte 
3. 
The polymer electrolyte is an electron and or ion-exchange polymer, for 
example, a polymer matrix containing a redox or reduction-oxidation 
couple. The polymer matrix is a polyalkene oxide. Polyethylene oxide has 
been tried and operates satisfactorily. Polyethylene glycol, polypropylene 
oxide, or polypropylene glycol also form suitable polymer matrixes. The 
redox couple is a polysulfide, e.g. polysulfide which has been used by the 
inventor is Na.sub.2 S.sub.4. Concentration of Na.sub.2 S.sub.4 in the 
electrolyte defined as a weight ratio, 0.25 grams of Na.sub.2 S.sub.4 for 
each gram poly(ethylene oxide), or as the ratio of oxygen atoms in the 
chain to the metal cation, the O/Na.sup.+ ratio was 8. Nothing is known at 
this time about the optimum ratio for maximum conductivity. Other couples 
may be used. The polymer electrolyte film was made on the CdS 1 by 
evaporation from a methanol solution, i.e. polyethylene oxide with a 
methanol solvent. The thickness of the polymer film is about 10 
micrometers. Contact with the CdTe semiconductor 2 is by direct physical 
contacting and heating under vacuum with a pressure of 1 kg/cm.sup.2. 
Electrical leads shown schematically as 5 and 6 in FIG. 1 are connected to 
the walls of the semiconductor films 1 and 2. The leads may be any 
convenient or conventional transparent electrical lead. If the incident 
light 4 falls on the semiconductor 1, then lead 5 is a grid, or 
transparent electrode, at least for those portions of the spectrum which 
are absorbed by the semiconductors 1 and 2. Lead 6 may also be transparent 
to permit light to enter from both sides of the cell. Alternatively, 
electrode 6 may be reflective itself or have reflective material on the 
far side from the light 4, in which case any non-absorbed radiation would 
be reflected and further absorbed. Electrodes 5 and 6 are connected to 
leads shown schematically and which in turn are connected to a load, shown 
here as volt meter 7. A substrate (not shown) is provided as well as 
suitable mechanical protection for the electrodes and semiconductors. The 
substrate and protective film must be transparent over that portion of the 
cell through which light passes. Glass is the usual substrate, although a 
plastic substrate in an encapsulation material may also be used. The 
electrode facing the incident light may have antireflection coating. 
FIGS. 2 and 3 are band diagrams of the device of FIG. 1. FIG. 2 shows the 
device in the dark, and FIG. 3 the band diagram under illumination. The 
band gap of n-type CdS is typically 2.4 eV. The band gap of p-type CdTe is 
typically 1.45 eV. At dark, the Fermi level .sup.E F is the same in both 
materials. Under illumination as shown in FIG. 3 with the incident 
illumination shown schematically by the wavy line with the legend 14, the 
Fermi levels shift, and there is a net potential across the semiconductors 
of V=.sup.E F.sup.(n) -.sup.E F.sup.(p). The two semiconductors have 
different band gaps. There is thus a multi-color cell which divides the 
solar spectrum into two parts, with the short wavelengths absorbed by the 
wide band gap semiconductor 1, and the long wavelengths absorbed by the 
narrow band gap semiconductor 2. The polymer electrolyte 3 permits the 
flow of charge there-across, and the two junctions 1-3 and 2-3 are in 
series. The maximum theoretical efficiency of the cell is about 35%. This 
can be compared with the best single junction photovoltaic cell commonly 
used having a theoretical efficiency of 25%, that being for gallium 
arsenide. The theoretical efficiency of a cadmium telluride cell by itself 
is 25%; and that of a cadmium sulfide cell by itself is 16%. 
The open circuit voltage measured by meter 7 reads 0.625 volts and a short 
circuit current of 35 uA/cm.sup.2 is obtained using 100 milliwatt/cm.sup.2 
Xenon light. 
Semiconductors of all categories are applicable to the cell of this 
invention i.e. elemental semiconductors (e.g. silicon, germanium); II-VI; 
III-V; tertiary compounds (GaAlAs, InCuSe.sub.2); layer compounds, 
transition metal dichalcogenides, (MoS.sub.2, WS.sub.2, MoSe.sub.2, 
WSe.sub.2); organic semiconductors (e.g. 1000 .ANG. phthalocyanines), 
polymeric semiconductors (e.g. polyacetylene). Single crystal, amorphous, 
or polycrystalline semiconductors can be used. It is a matter of balancing 
good semiconductors with the right combination of (a) band gaps, (b) work 
functions, and (c) electron affinities in order to have the right 
absorption characteristics and to arrive at good rectifying junctions. 
Determination of the resistances or the dopant concentrations at this stage 
is a matter of optimizing the relative resistances in the cell, i.e. it 
depends on the resistance of the polymer film, which in turn depends on 
the polymer used. An average is somewhat higher than the resistances used 
in traditional photovoltaic cells, e.g. 10-50 ohm-cm. 
Turning now to FIG. 4, there is shown an electrolytic Schottky barrier 
device or "half-cell" of the invention. In this embodiment there is an 
individual junction. The embodiment of FIG. 4 is similar to the one of 
FIG. 1 except that one of the semiconductors is replaced by a metal or 
counter electrode 21. Electrode 21 is a thin metal film or grid which is a 
semi-transparent or other transparent counter electrode, e.g. tin-oxide or 
indium-tin-oxide, and is preferably completely transparent to that portion 
of the spectrum which is to be absorbed. Suitable metals and oxides 
include Cr, Al, Cr/Cu alloy, Mg, Au, indium-tin-oxide, tin oxide. Layer 22 
is either p-type or an n-type semiconductor, and all semiconductors are 
applicable. A polymer electrolyte 23 separates the transparent counter 
electrode 21 and the semiconductor 22. A transparent cover for example, 
glass 25 or an antireflection coating is on an outside face of the counter 
electrode 21. A conducting base electrode 26 is on an outside face of the 
semiconductor 22. Light 24 passes through the transparent cover 25, 
transparent electrode 21, and electrolyte 23 and is absorbed by the 
semiconductor 22. The device of FIG. 4 is an electrolytic Schottky barrier 
cell and may have a higher open circuit voltage than that of the solid 
state junction cells. 
The band diagram of the device of FIG. 4 is shown in FIGS. 5 and 6 with n- 
and p-type semiconductors, respectively; and with light impinging upon the 
semiconductors. The flow and direction of holes, h.sup.+, and electrons, 
e.sup.-, are shown in the semiconductor region. The voltage across the 
electrodes 21, 26 at open circuit is V=E.sub.F.sup.semi .sub.- 
E.sub.F.sup.metal for the n-type semiconductor, and V=E.sub.F.sup.metal 
-E.sub.F.sup.semi for the p-type. 
The Schottky barrier `half-cell` may also be a backwall type cell, i.e. the 
light is incident on the semiconductor which is a thin film on a 
transparent conductive substrate. The counter electrode and the polymer in 
this case do not have to be transparent. 
FIGS. 7 & 8 show two further embodiments of cells, both having multiple 
junctions in tandem. The cells discribed in FIGS. 1, 2, & 3 are stacked in 
series and include more than two different band gaps. They may be 
independent cells connected in series with a transparent conductive 
substrate between the various cells as shown in FIG. 7; or, as shown in 
FIG. 8, the electrical contact may be made by further polymer films. 
In FIG. 7, there are shown four semiconductive thin films 71, 72, 73 and 
74. Films 71 and 72 are separated by polymer thin film electrolyte 75; and 
semiconductors 73 and 74 by electrolyte 76. A transparent conductive 
electrode 77 is a spacer between semiconductors 72 and 73. Electrodes 5 
and 6 are connected to the outer face of semiconductors 71 and 74. 
Electrodes 5 and 77 are transparent conductive electrodes. 77 may be two 
separate electrodes connected in series. Incident light is shown, by the 
legend hv, and the wavy arrow, falling upon electrode 5, and passing 
through the entire cell. 
The band gap of the semiconductor 71 is greater than the band gap of the 
semiconductor 72, which is greater than that of semiconductor 73, and 
greater than that of 74. 
EQU .sup.E g(71)&gt;.sup.E g(72)&gt;.sup.E g(73)&gt;.sup.E g(74) 
with hv incident on 71. 
Polymer films 75 and 76 may be identical or different. The order of n and p 
types may, of course, be interchanged. The electrode 6 does not have to be 
transparent. 
Voltmeter 7 is shown connected to the electrodes 5 & 6, and the voltage 
measured across that meter 7 is the sum of the potentials V.sub.71, 
V.sub.72, V.sub.73 and V.sub.74 developed across or by the semiconductors 
71-74. FIG. 7 is not to scale, and electrode 77 is shown in the figure of 
an exaggerated width order to show the electrical levels between the 
semiconductors 72 & 73. 
FIG. 8 shows three semiconductive thin films 81, 82 and 83, separated 
respectively by two polymer thin films 84 and 85. The outer walls of the 
semiconductors 81 and 83 have a transparent conductive film 5 and a 
conductive film 6 respectively. The band gap of semiconductor 81 is 
greater than the band gap of semiconductor 82, which is greater than the 
band gap of semiconductor 83. Incident light hv impinges the transparent 
conductive electrode 5 which is connected to the widest band gap or first 
semiconductor 81 and passes through the array. 
.sup.E g(81)&gt;.sup.E g(82)&gt;.sup.E g(83) with light hv incident on 81. 
As in previous figures there is shown a voltmeter 7, connected to the 
electrodes 5 & 6, and which measures the potential produced by the three 
semiconductors so that 
EQU V=V.sub.81 +V.sub.82 +V.sub.83. 
Instead of NPP semiconductors the semiconductors may be PNN. The polymer 
matrix may be the same for polymers 84 and 85, but the molecular or ionic 
species will be different; one producing a rectifying contact to 
semiconductor 82, the other an ohmic non-rectifying contact. For example, 
film 85 makes ohmic contact, i.e. nonblocking contact, to the second 
semiconductor 82; and a rectifying barrier junction with the third 
semiconductor 83. Semiconductor 83 has a larger work function than 
semiconductor 82, if both are p type. The work function is defined as the 
distance in energy between the vacuum level and the top of the valence 
band of the semiconductor. If both semiconductors 82 and 83 are n-type, 
then semiconductor 83 must have a smaller electron affinity than 
semiconductor 82. The electron affinity is defined as the distance in 
energy between the vacuum level and the bottom of the conduction band of 
the semiconductor. Semiconductors 82 and 83 must be of the same type, for 
the flow of electrons to have the same sense in both semiconductors. 
Semiconductor 81 and semiconductor 82 are of the opposite type. The 
semiconductor 81 can be n-type or p type. The band gaps are arranged 
according to E.sub.g(81) is greater than E.sub.g(82) which is greater than 
E.sub.g(83), where semiconductor 81 faces the incident light. The three 
level cell of the type shown in FIG. 8 has a theoretical efficiency of 
approximately 40 %, without concentration of sunlight. 
Similarly, the number of cells is not limited to what is shown in FIGS. 7 & 
8, but more semiconductors may be added further in tandem to produce 
multi-color cells of higher order. III-V compounds may be particularlly 
well suited for this type of manipulation of band gaps and electron 
affinities. 
A tandem cell may also be constructed by beginning with a Schottky cell, 
barrier cell, i.e. by substituting a transparent counter electrode for the 
first semiconductor cell 71 in FIG. 7 or 81 in FIG. 8, and adding polymer 
films followed by semiconductors as described above. 
The cells described may also be used with systems which concentrate light 
onto a small area. The advantages of multicolor cells, or tandem cells, 
are even larger with concentrator systems. The efficiency of the cells is 
higher, and the added cost of producing the more complex cells may be 
offset by using cheap concentrator systems, e.g. plastic fresnel lenses. 
The higher efficiency is due to the following: As the number of cells 
increases, the photon flux available for absorption in any one 
semiconductor in the stack decreases, which leads to a lowering of the 
photovoltaic conversion efficiency of each junction. The total photon flux 
incident on the tandem cell stack can be increased by using concentrating 
mirrors and lenses, thus circumventing this efficiency reduction. 
The tandem cell concept is particularly compatible with solar concentrator 
systems. It should be pointed out, however, that the efficiency of the 
stack still increases with the number of cells relative to the efficiency 
of a cell based on a single junction. The production process may lead to 
inexpensive thin film tandem cells which may make concentrating systems 
economically unnecessary. The efficencies which are approximately 25% for 
1 cell, 35% for 2 cells, 40% for 3 cells are efficiencies calculated with 
no concentration, i.e. 1 sun. For a concentration factor of a hundred, 
i.e. 100 suns, the corresponding numbers are 30%, 42%, and 48%. The 
numbers vary somewhat depending on the method of calculation but the trend 
is evident. One reaches a limiting value of about 70% for an infinite 
number of cells. 
An advantage of this invention is the ability to make the cells all thin 
film, (e.g. the thickness can be a few micrometers or less.) Single 
crystals may be used as well as amorphous or polycrystalline materials. 
The thickness of the semiconductor material depends on (a) the 
absorptivity of the material (how thick to absorb all the light of energy 
above the band gap), and (b) the diffusion length (if light is absorbed on 
the opposite side of the junction as in the CdS in the example, the 
charges will have to diffuse to the junction region on the other side in 
order to be collected). For silicon, for example, this means a thickness 
of about 100 micrometers, and for GaAs or CdS, about 2-3 micrometers. 
The polymer film will be less than 1 micrometer thick, (even less than 0.1 
micrometer) depending on its resistivity and deformability. 
Many redox couples can be used, e.g. I.sup.-.sub.3 /I.sup.-, TCNQ.sup.- 
/TCNQ. These redox species with a single charge can be transported as ions 
through the polymer. Ions with multiple charges may interact too strongly 
with the matrix to have ionic mobility but at high concentrations may 
provide electronic conductivity by hopping or tunneling between the 
molecules. In this case, applicable multiple charged redox species include 
e.g. Fe.sup.2+ /Fe.sup.3+, Fe(CN).sup.3- 6/Fe(CN).sup.4-.sub.6, Quinone 
(Q/QH.sub.2), and others. 
Polymers to be used can be grouped in five catagories. 
(i) For solution produced films, insulating polymers with high dielectric 
constants and therefore high solubility for ions are applicable for the 
production process described. Polymers with sulfonic groups are good, i.e. 
sulfonic polymers. 
(ii) Electronically conductive polymer films with ions dissolved in the 
polymers, e.g. polyacetylene. The combination of electronic and ionic 
conductivity imparts higher mobility to the ionic species in order to 
preserve space charge neutrality in the film. There is at the moment 
ongoing research with the aim of using polyacetylene for ion transport. 
This is essentially a new use of a new class of polymers. 
(iii) Poly(phenylene oxide) incorporating ferrocene. These films are 
produced by electrochemical oxidation on metal surfaces. They may be 
produced on the transparent counter electrode. Then the semiconductor 
material is placed on top of the polymer, n- or p-type. Alternatively, the 
doped polymer may be produced directly on the surface of an n-type 
material by the process of photo-electro-oxidation by illuminating with 
light of energy higher than the band gap of the semiconductor. An anodic 
(positive) polarization is applied to the semiconductor in order to drive 
the minority carriers (holes) to the semiconductor/electrolyte interface 
to perform the oxidation of the monomer in solution to polymer, which 
deposits onto the semiconductor surface. The polymer itself is insulating. 
Molecules can be incorporated into the polymer matrix from the same 
solution. The resulting polymer film is uniformly doped with molecules or 
ions and therefore forms a rectifying barrier with a semiconductor. This 
process is applicable to other insulating polymer matrices than 
poly(phenylene oxide) and to other dopants than ferrocene. An example of 
this process for a different type of polymer, is the electronically highly 
conductive polymer of polypyrrole. 
An equivalent process is photo-electroreduction on the surface of p-type 
semiconductors. The absorbed light of energy larger than the band gap of 
the semiconductor produces electron-hole pairs. Cathodic (negative) 
polarization on the semiconductor makes the minority carriers (electrons) 
flow to the semiconductor/electrolyte interface and can be used to reduce 
monomers in solution to polymers on the surface incorporating dopant 
molecules or ions from the solution. The process is thus a one-step 
oxidation or reduction and doping. An example of this process is the 
electrochemical reduction of acrylonitrile to polyacrylonitrile. 
The polymers which can be photoelectropolymerized on n-type semiconductors 
in the manner described above can be polymerized on p-type semiconductors 
as well by anodic polarization without light. Similarly, the polymers 
which can be photoreduced on p-type semiconductors can be reduced directly 
by a negative voltage on the surfaces of n-type semiconductors. 
(iv) Polymers with pendant groups attached to the backbone of insulating 
polymers, e.g. TTF substituted polystyrene copolymer. The energy levels 
which interact with the semiconductor to produce a junction are defined by 
the pendant molecules which, in high concentrations, produce electronic 
conductivity by hopping or tunneling. These energy levels can be adjusted 
by substituting different pendant groups. 
(v) Various polymer production techniques may be used, including (i) 
Solvent evaporation: (spin-coating is used to produce thin uniform films. 
This has been used with pendant group polymers and with poly(ethylene 
oxide). (ii) Glow discharge polymerization. (iii) Oligomerization during 
surface chemical reaction. (iv) (Irreversible) adsorption of polymer 
films. (v) Plasma polymerization. (vi) Electrodeposition, and (vii) 
Functionalization of surface bound polymers. Several techniques may be 
combined either at the same junction or at successive junctions. 
Poly(ethylene oxide), for example is soft and a very thin coating may not 
have the rigidity required for assembly. A very thin layer of a more 
highly conductive polymer is photoelectropolymerized on a face of one or 
both of the semiconductors and a soft material e.g. poly(ethylene oxide) 
is between the two. 
Techniques for producing semiconductor thin films include these techniques 
for making the semiconductor film directly on top of the polymer film, 
which has been made on a transparent electrode or the opposite 
semiconductor. They include (i) Spray pyrolysis (solution spraying). This 
requires substrates held at elevated temperatures, sometimes up to 
400.degree. celcius, and requires polymers which can withstand such high 
temperatures. (ii) Silk screening (seriographic) techniques. (iii) 
Deposition from aqueous solution. Solution of ions precipitate as 
semiconductor films on top of the substrate. This has been demonstrated 
for a numbmer of II-VI compounds, e.g. CdS, CdO, ZnO, and is not a high 
temperature process. (iv) Cathodic codeposition of different elements 
using the polymer coated electrode as cathode. This has been demonstrated 
for CdSe (without polymers on the electrodes). It involves an aqueous 
solution and is therefore not a high temperature process. (v) Anodic 
formation of semiconducting films by using the polymer coated electrode as 
an anode in aqueous solution. This has been demonstrated for CdS and 
Bi.sub.2 S.sub.3. This is not a high temperature process. 
FIG. 9 shows an alternative embodiment of the cell of this invention. Two 
semiconductor films 91 and 92, for example, n & p type respectively, are 
separated by a thin film electrolyte 93, e.g., a polyethylene oxide redox 
couple. On one, or both sides of the film 93, there is a highly conductive 
polymer 94. In FIG. 9, the highly conductive polymer 94 is shown on both 
sides, however, it need not be on both. The film 94 is a highly conductive 
polypyrrole doped with a suitable transportion, for example, 
BF.sup.-.sub.4 or ClO.sup.-.sub.4. Other films include polyphenylene-oxide 
doped with ferrocene; or polyphenylene sulfide doped with ferrocene. 
Alternatively, the films 94 may be a thin film metallic layer, for 
example, gold, silver, or platinum. In the case of the highly conductive 
polymer, the film is several hundred angstroms thick. If the film is 
metallic, it is a few angstroms to a few hundred angstroms thick. The 
conductive polymer film 94 on either side of the film 93 may be the same 
or of different types. The film 94 has a work function such as to make a 
rectifying energy barrier within the semiconductor. Of course, the thin 
films 93 and 94 must be transparent, and that controls the maximum 
thickness. 
One may view the embodiment of FIG. 9 as at least one semiconductor with a 
highly conductive film 94, adjacent to which and together with is the film 
93 and the other half of the tandem or multiple cell. 
In all the cells of all the figures the polymer electrolyte is not limited 
to ion conductors, but any polymeric conductor is suitable, so long as it 
be capable of conducting electricity and is not limited to the ionic ones. 
This is sometimes termed any solid polymer electrolyte. 
In FIG. 9 it should be noted that the Fermi level in the band diagram of 
the layers 93 and 94 is constant and does not shift in both the dark and 
under illumination. Of course the Fermi levels in the two semiconductors 
91 and 92 do shift during illumination, and this of course produces the 
voltage across the cell. 
An example can be given of the formation of highly conducting polypyrrole 
on the suface of n type silicon. The method is applicable to other 
combinations of polypyrrole and polymers on semiconductor materials. 
Pyrrole can be polymerized onto the surface of metal electrodes and doped 
to a conductive form by a one-step electrolytic oxidation of pyrrole in 
acetonitrile solution using a tetraethylammonium tetrafluoroborate 
electrolyte. Dark electrolytic oxidation on an n-type semiconductor is 
impossible because the oxidation potential of pyrrole lies at a higher 
positive potential than the flat band potential or the conduction band 
edge of the known semiconductors. The oxidation of pyrrole to polypyrrole 
on an n-type semiconductor surface is carried out by illuminating the 
semiconductor with light of an energy higher than the band gap and 
applying a small anodic bias. The minority carriers generated by the light 
absorption migrate to the semiconductor-electrolyte interface where they 
oxidize the pyrrole which in turn deposits onto the surface as 
polypyrrole. The polymer is uniformly doped by anions from the electrolyte 
to a highly conductive form or a p-type semiconductor depending on the 
solution concentration of the dopant. It is produced on single crystal, 
polycrystalline, or amorphous semiconductors. 
FIG. 10 is a band diagram, (Similar to FIG. 5) of a modification of the 
cell of FIG. 4, to improve the rectifying junction between semiconductor 
and electrolyte. 
The doping in the semiconductor is varied in order to produce a 
semiconductor surface layer of higher resistivity than the polymer 
electrolyte. An n-type semiconductor would have the designation n/n.sup.+ 
which denotes a layered structure of a lightly doped film (n) on top of a 
more heavily doped substrate (n.sup.+) of the same material. Examples of 
lightly doped are 10.sup.2 -10.sup.6 ohm-cm and heavily doped 0.01-10 
ohm-cm. The thickness of the lightly doped layer is as thick as a few 
micrometers (2-3 .mu.m) or as thin as 1000 Angstroms. This structure also 
provides a back surface field to help in the separation of the charges. 
In FIG. 10, the electric fields are represented as slopes of the energy 
bands of the semiconductor. The back surface field has the same direction 
as the field at the interface, and thus aids in the charge separation for 
that part of the light which is absorbed further into the semiconductor. 
For p-type semiconductors the structure would be p/p.sup.+, exactly 
equivalent. 
The resistive surface layer may be made epitaxially on the more conductive 
substrate. If the semiconductor is a film (e.g. made by evaporation or 
sputtering), the dopant concentration may be varied by varying the rate of 
evaporation from the dopant source. If the semiconductor is made by 
electrolytic deposition, the dopant concentration can be varied by 
changing the dopant concentration in the electrolyte. 
The counter electrode is transparent and can be a thin metal film on glass 
(e.g. Au, Pt, Pd, Co) 50-150 Angstroms thick, a conductive oxide (e.g. 
indium-tin-oxide or tin-oxide), or a conductive oxide with a very thin 
metal film to enhance the charge transfer capabilities (e.g. 5-100 A of 
Pt, Pd, Au, Co). 
This structure has a higher resistivity in the semiconductor surface layer 
than in the electrolyte. Thus the built-in voltage across the junction 
falls across the semiconductor rather than the electrolyte. This electric 
field across the surface layer of the semiconductor is necessary for 
efficient separation of the photogenerated charges. 
FIG. 11 is a band diagram (similar to FIG. 10) of a further modification of 
the cell of FIG. 9. 
A rectifying junction is made by depositing a transparent, highly 
conductive film 111 on the surface of the semiconductor. The film can be a 
highly conductive polymer (e.g. polypyrrole) or a metal (e.g. Pt, Au). For 
an n-type semiconductor substrate the material must have a high work 
function (electronegativity) and for a p-type semiconductor the material 
must have a low work function (electronegativity) in order to make a 
rectifying junction with the semiconductor. The thickness of the polymer 
is typically 100-1000 A and for the metal 5-150 A. 
The n/n.sup.+ structure of FIG. 10 may be employed in addition to the 
surface modification. The situation for a p-type semiconductor is exactly 
equivalent. 
It is advantageous to modify the surface with a very thin film of metal 
(e.g. Pt) of 2-3 A to 50 A thickness before depositing the polymer, 
especially when using n type Si with polypyrrole deposited from aqueous 
electrolyte. 
The double cell fo FIG. 1 may include the modification of FIGS. 10 and 11. 
In FIG. 1, the (modified) semiconductor replaces the counter electrode, 
the second semiconductor will be of different band gap than the original 
and of opposite type, light being incident on the back side of the wide 
band gap semiconductor which has a transparent ohmic (non-rectifying) 
contact. Similarly, the modifications of FIGS. 10 and 11 may be applied to 
the cells of FIGS. 7 and 8. 
FIG. 12 is a diagram illustrating method of manufacturing highly conductive 
and transparent polymer films; for example the photoelectrochemical 
generation of thin conductive polymer films (e.g. polypyrrole) on n-type 
semiconductor (e.g. n-Si) using light absorbed by the semiconductor. 
A semiconductor 120 is immersed in a solution 121 which contains the 
monomer (the building blocks of the polymer chain) and a supporting 
electrolyte which contains the species to be used as dopant for the 
polymer. The light is absorbed by the semiconductor, and generates 
electron-hole pairs (h.sup.+,e.sup.+). A positive potential from a source 
122 on the semiconductor drives the holes to the semiconductorelectrolyte 
interface. The hole reaching the interface takes an electron from 
(oxidizes) a monomer in the solution. A polymer film will then grow by 
this electro-oxidation process on the surface of the substrate. 
Electro-oxidation has been known on metal surfaces (where light is not 
needed) for a number of different polymers (see list at the end of this 
section). The process is used for polypyrrole, polyaniline and 
polythienylene on semiconductors. Exactly how the process occurs on the 
molecular level is not yet known. 
The monomer concentration (e.g. pyrrole) is typically 0.01 Molar to 1.0 M, 
and the supporting electrolyte contains the ions to be used as dopants 
(e.g. BF.sup.-.sub.4, ClO.sup.-.sub.4, I.sup.-, Br.sup.-, Cl.sup.-) 
typically in concentrations 0.01-1.0 M. The dopant molecules (e.g. 
BF.sup.-.sub.4) will be included in the film as it is being made. The 
dopants will be acceptors (of electrons). 
The doping may also be done from the gas phase of the dopant. It may also 
be done electrochemically after the film is made. 
The solvent is an organic solvent (e.g. acetonitrile, dimethylformamide, 
dimethylsulfoxide, propylene carbonate, methanol) or water. It may also be 
a mixture (e.g. acetonitrile+pyridine). 
The doping and the manufacturing of the polymer films may thus be a 
one-step process. The polymer films will continue to grow only as long as 
the light is on and the film is not yet thick enough to absorb all the 
incident light. Thick films become black and non-transparent because they 
are highly conductive. 
A negative potential on an illuminated p-type electrode drives the 
photogenerated electrons to the interface where they reduce (add an 
electron to) a monomer species in solution which then builds a polymer 
film on the surface of the semiconductor. The dopant in this case will be 
an electron donor (e.g. Na, K). 
Several films can be made in the same manner: 
Polyaniline 
The monomer is aniline, the concentrations and the solvents and the 
procedures are the same. 
Substituted Anilines 
##STR1## 
R.sub.1 -R.sub.5 each are a member of the following chemical groups: 
para-CH.sub.3, para-OCH.sub.3, ortho-CF.sub.3, meta-CF.sub.3, para-COOH, 
ortho-NH.sub.2, para-NH.sub.2. 
Other substituents are also applicable, e.g. p-toluidine, p-anisidine, 
2-aminobenzotorifluoride, 3-aminobenzotrifluoride, p-aminobenzoic acid, 
p-phenylenediamine, and o-phenylenediamine. In the case of aniline, the 
parent compound, all the R.sub.1 -R.sub.5 are H, hydrogen. 
Polyphenylene oxide (PPO) 
##STR2## 
R.sub.1 -R.sub.5 can be hydrogen or substituent groups. Dubois et al. have 
studied alcohol substituents, alkyl radical substituents, hydroxy-or 
carboxymethylated groups (ref. 4). 
The medium is e.g. Methanol - 0.15 Molar NaOH containing 0.2 Molar 
concentration of the monomer to be polymerized. In principle the same 
solvents and concentrations as well as the dopants used with the anilines 
and pyrrole are applicable. There is higher electrical conductivity when 
the ferrocene is in the solution. 
Poly (2,5-thienylene) (or polythiophene) 
The monomer is thiophene, which can be polymerized photoelectrochemically. 
##STR3## 
Certain polymer films can be made by condensation from the gas phase, e.g. 
(SN).sub.x or polysulfurnitride, where the (SN).sub.x source is held at 
135-150 degrees centigrade and the surface to be polymerized at 
15.degree.-20.degree. C. 
Other polymer films can be made by gas phase ionization or plasma 
polymerization, by an electric discharge in a gas of the monomer. 
The thin transparent metal films are made as follows: If the semiconductor 
surface is modified by a metal film the film can be made by deposition in 
vacuum (thermal evaporation or sputtering) or electrolytically from a 
solution containing ions of the metal to be deposited. The thickness of 
the metal film can be from 2-3 Angstroms to 150 Angstroms. The metals 
traditionally used have been Pt, Pd, Au, Mg, Cr, Al, Cs, Cr-Cu allous. 
Metal oxides which have been used include indium-tin oxide and tin oxide. 
The polymer electrolyte used is an electron or ion exchange polymer, e.g., 
a polymer matrix containing a redox reduction-oxidation couple, and 
includes: 
1. Polyethers: polyethylene oxide and polypropylene oxide. 
The films are cast from solutions containing dissolved redox couples, e.g., 
iodine (I.sup.-.sub.3 /I.sup.-), bromine (Br.sup.-.sub.3 /Br.sup.-), 
tetracyanoquinodimethane (TCNQ.sup.- /TCNQ), and polysulfides (e.g. 
Na.sub.2 S.sub.4) all of which are good candidates for ion exchange 
couples. 
More speculative are iron (Fe.sup.2+ /.sup.3+), ferricyanide 
(Fe(CN).sub.6.sup.3-/4-), and Quinone (Q/QH.sub.2). These are multiply 
charged and may not transport through the matrix. However, at high 
concentrations they may conduct via electron hopping. 
2. Polyurethanes made from polyethylene glycol and polypropylene glycol. 
3. Polyacetylene. 
4. Polyhydroxyphenylene, which conducts via electrons and ions and falls in 
the same category as polyacetylene. 
5. Polymers with electroactive groups attached to the polymer backbone, 
e.g. phenoxytetrathiafulvalene. Tetrathiafulvalene (TTF) groups are 
attached to the polystyrene backbone. This polymer is a very good medium 
for transporting ions. Polystyrene itself is an insulator. Attaching other 
groups than TTF changes the charge transfer properties and allows for 
possibly optimising the ion exchange polymer, i.e. different groups 
corresponding to different redox energy levels, which in turn are matched 
with the semiconductor energy levels. 
6. Polysulfone. This is a substitute for the polyethers. 
7. Cellulose acetate. 
8. Poly (gamma 8-methyl L-Glutamate). 
Semiconductors of all categories are applicable to the cells: 
1. Elemental semiconductors: Si, Ge 
2. II-VI compound semiconductors (from the columns II and VI in the 
periodic table): Cadmium sulfide (CdS), Cadmium Telluride (CdTe), CdSe, 
ZnSe, ZnTe. 
3. III-V compounds: GaAs, GaP, InP, AlAs, AlP. 
4. III-V ternary alloys: GaAlAs. 
5. Tertiary compounds: CuInS.sub.2, CuInSe.sub.2. 
6. Transition metal chalcogenides: WS.sub.2, WSe.sub.2, WTe.sub.2, 
MoS.sub.2, MoSe.sub.2, MoTe.sub.2, ZrS.sub.2, ZrSe.sub.2, etc. 
7. Other inorganic semiconductors: Bi.sub.2 S.sub.3, Zn.sub.3 P.sub.2, CuO, 
CuS.sub.2. 
8. Organic semiconductors: anthracene, tetracene, pentacene, etc. 
9. Pigment films: Cyanines, phthalocyanines, hydroxysquarylium etc. 
10. Polymeric semiconductors, e.g., polyacetylene, polyacrylonitrile. 
Single crystals, polycrystalline, and amorphous films, in particular 
amorphous Si, are all applicable. Dopant concentrations will be optimized 
for each particular interface. 
Thus, there has been shown described several novel photovoltaic cells using 
solid electrolytes. Polymer electrolytes are a new concept in 
photoelectrochemical cells for the conversion of solar energy to 
electricity. It is envisioned that this is a basic invention of such 
devices and the invention should not be narrowly interpreted during the 
life of any patent. Those following the teachings of this application will 
no doubt be led to other and additional polymer electrolytes and other 
semiconductors than those specifically described herein (which are the 
ones that have been employed by the inventor in his research to date). 
FIG. 13 is similar to FIG. 9. It shows an n-type semiconductor 131, a 
p-type semiconductor 132, a dry solid polymer electrolyte 133, and a 
highly conductive layer 134. The layer 134 increases the interfacial 
contact area and between the semiconductor 131 and the adjacent 
electrolyte 133, and also produces an improved charge transfer 
characteristic at this interface and of the whole device. The highly 
conductive layer is a polymer blend of a highly conductive polymer, e.g. 
polypyrrole and a solid polymer electrolyte, e.g. polyethylene oxide 
complexed with potassium iodide. In the blend 134, the polymer electrolyte 
component 134 penetrates into the conductive polymer component 133 
resulting in increased contact area, and thus better charge transfer 
across the interface. The film 133 is for example, several hundred to 
10,000 angstroms thick; and layer 134 is 100 to 1000 angstroms thick. Both 
layers are essentially transparent. 
The polymer blend 134 is synthesized directly on the surface of the 
semiconductor 131 by a technique of photoassisted electrochemical 
oxidation from a solution of the monomer of the highly conductive polymer 
and the polymer electrolyte in its complexed form. The resulting 
polymerization of the highly conductive polymer, e.g. with the complexed 
polymer electrolyte present in solution produces a polymer blend of the 
two polymer phases. 
A method of manufacturing the basic cell is as follows, with the improved 
blend. The semiconductor 131 may be coated with a thin layer of platinum, 
e.g. 5-50 angstroms. This is particularly desirable where the n silicon is 
single crystal. The platinum layer may be provided e.g. by vacuum 
evaporation, or electrolytic deposition. The platinum layer produces a 
better electronic and physical coupling between the semiconductor and the 
polymer and thus leads to better charge transfer. If the semiconductor 
layer 131 is amorphous or polycrystalline silicon, then the platinum may 
also be used. The semiconductor may be any of those listed previously in 
the specification, for example CdSe, CdTe, and CdS. If the layer 131 is 
p-type silicon, a low electronegativity metal may be used, e.g. indium or 
aluminum. 
A solution is formed containing (i) acetonitrile as solvent,(ii) Et, NBF, 
(tetraethylammonium tetrafluoroborate), (e.g. 0.01-1.0 Molar), (iii) 
Pyrrole (0.01-5.0 Molar), (iv) 0.01-3.0% PEO by weight; molecular weight 
of PEO may be 10.sup.4 -5.times.10.sup.6 ; (v) KI in a ratio of 4.5-8 
polyether oxygen atoms per potassium atom, and (vi) I.sub.2 in a ratio of 
KI:I.sub.2 =4:1. The substrate 131, with or without the platinum layer, is 
immersed into the solution and the semiconductor is held at 0.5 volts or 
higher potential, versus the standard calomel reference electrode. 
The member 132 in FIG. 13 of the, completed cell may be another p type 
semiconductor, or a counter electrode comprising glass with a transparent 
conductive coating, e.g. indium tin-oxide (ITO), or platinum, or chromium, 
or other material as mentioned previously. The counter electrode may be 
coated, especially when it is ITO, with a thin layer of platinum, e.g. 5 
to 50 angstroms for better charge transfer to the solid polymer 
electrolyte. When ITO is the counter electrode, the platinum is needed 
because ITO is an insert electrode with the iodine redox couple. 
The element 132, whether a counter electrode on a glass support, or a 
semiconductor, or a web filled with charge carriers, (1) may be coated 
with platinum or chromium or other metal layer; or (2) may have a blend of 
polymer of a type described herein in place of such metal layer; or (3) 
may in addition to the platinum or other metal layer, have a layer of 
polymer blend on top. 
Once the semiconductor layer 131 has been formed with the polymer blend, 
and the right hand member 132, prepared (whether bare, or with a layer of 
metal and/or a layer of polymer blend on the face thereof); the next step 
is to form the dry solid polymer electrolyte 133. A film of polyethylene 
oxide complexed with, (or doped with), potassium iodide and iodine is 
solution cast by solvent evaporation from acetonitrile solution, for 
example, by spin coating. The thickness when dry is in the range of 0.01 
to 1.0 microns. The polymer electrolyte may be formed on the polymer blend 
film 134, or on the surface (bare or prepared) of elements 132 or on both. 
The two halves of the cell 131-134 and 132 are then contacted to each 
other by heating to 70.degree.-100.degree. Celsius under vacuum with 
pressure about 1 kg/cm.sup.2 for ten minutes to ten hours. 
Thus, it will be appreciated that the dry solid polymer electrolyte 133 is 
adjacent to the polymer blend 134 (which is a composite of dry solid 
polymer electrolyte with the highly conductive polymer). During the step 
of forming the polymer blend 134, there was an electrochemical 
polymerization of polypyrrole in a solution containing PEO-KI/I.sub.2. 
Polyethylene oxide is a polymer soluble in acetonitrile. As the 
polypyrrole film grows, it entraps the PEO-KI/I.sub.2 phase within it, 
resulting in a polymer blend of polypyrrole and PEO-KI/I.sub.2. 
A modification of the method just described may be achieved by using a 
different complexing salt for PEO. The reason is to avoid two competing 
paths for the current to flow: 
(i) polymerization of pyrrole (2.2-2.4 electrons per pyrrole monomer). 
(ii) oxidation of the iodide in the electrolyte solution, i.e. 
2 h.sup.+ +3 I-.fwdarw.I.sup.-.sub.3 at the semiconductor surface 
2 e.sup.- +I.sub.3.sup.- .fwdarw.3I.sup.- at the counter electrode, where 
h.sup.+ designates a hole and e.sup.- designates an electron. 
Reaction (ii) is a parasitic reaction which lowers the yield of the 
polymerization. This may be improved as follows: 
(a) Polymerize from a solution of what has been previously described plus 
PEO complexed with KNO.sub.3, (alternatives are NaNO.sub.3, KCl, NaCl, 
KC1O.sub.4, NaClO.sub.4, NaBF.sub.4, KBF.sub.4) NO.sup.- 3 and the other 
anions are not electroactive at the potentials in question and should not 
therefore contribute a parasitic current. 
(b) Upon contacting the polymer blend of polypyrrole and PEO with a film of 
PEO-KI/I.sub.2 an electrochemical exchange of anions will automatically 
take place, giving a polymer blend of polypyrrole and PEO-KI/I.sub.2, i.e. 
the NO.sub.3 will diffuse out of the blend and the iodide will diffuse in. 
FIG. 14 is an enlarged highly schematic view of the cross-section showing 
the blend. This is an artistic representation of what is believed the 
blend looks like, with long strands of polypyrrole e tending outward from 
the platinum layer 135. Like elements in both figures bear like legends. 
Various alternatives may be used, some of which are indicated above in the 
specification. They include, alternative materials for the dopant such as 
NaI for KI; for the highly conductive polymer, polyindole, polyazulene, 
polythiophene and polyfuran; and for the solid polymer electrolyte, 
polypropylene oxide for PEO. 
An electric battery cell can also be constructed in which polyacetylene 
suitably doped is used in place of the semiconductor 131 and 132. Doping 
for example is with sodium and iodide ions. A polyethyleneoxide solid 
electrolyte is used, and the polymer blend at one or both faces of the PEO 
is polyacetylene - polyethylene oxide. An alternative cell is with doped 
polyparaphenylene as elements 131 and 132, doped PEO as polymer 
electrolyte and a blend of polyparaphenlene and polyethylene oxide formed 
at the interfaces between the polyparaphenylene and polyethylene oxide. 
Thus, there has been described an improved cell having increase in 
interfaciai contact area and improved charge transfer characteristics due 
to the polymer blend between the solid polymer electrolyte electrodes, and 
the adjacent counter electrode and or semiconductors.