GB1602889A

GB1602889A - Semiconductor photovoltaic generator and a method of manufacturing same

Info

Publication number: GB1602889A
Application number: GB23989/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-11-18

Description

(54) A SEMICONDUCTOR PHOTOVOLTAIC GENERATOR AND A METHOD OF MANUFACTURING SAME (71) We, NIKOLAI STEPA NOVICH LIDORENKO, of kvartira 127, 3 Mytischinskaya ulitsa, 14a, Moscow, VLADIMIR MIKHAILOVICH EVDOKIMOV, of kvartira 77, Anadyrsky prospekt, 67, Moscow, VITALY VIKTOROVICH ZADDE, of kvartira 120, 9 linia, 3, poselok Severny, Moscow, ALEXANDR IVANOVICH KOZLOV, of kvartira 66, ulitsa Mikhailova, 5, Moscow, STANISLAV VASILIEVICH RYABIKOV, of kvartira 64, pereulok Vasnetsova, 12, Moscow, VALERY NIKOLAEVICH POTAPOV, of kvartira 213, ulitsa Timiryazevskaya, 13, Moscow, DMITRY SEMENOVICH STREBKOV, of ulitsa Luganskaya, 21, Moscow, TATIANA IVANOVNA SURIANINOVA, of kvartira 113, Dmitrovskoe shosse, 25, Moscow, BORIS ALEXANDROVICH CHUBRIKOV, of kvartira 160, ulitsa Fedora Poletaeva, 25, Moscow, VALENTINA VASILIEVNA ZATRAVINA, of derevnya Belyaninovo, 6, Mytischinsky raion, Moskovskaya oblast, BORIS VASILIEVICH KOROLEV, of kvartira 208, Shenkursky proezd, 8, Moscow, VIKTOR FEDOROVICH KULIKOV, of kvartira 56, ulitsa Komarova, 11-b, Moscow, LARISA LEONIDOVNA ZHURAVLEVA, of kvartira 64, ulitsa Bochkova, 8, Moscow, VADIM ALEXEEVICH UNISHKOV, of kvartira 162, korpus 1, ulitsa Bazhova, 15, Moscow, ANATOLY ALEXEEVICH DORMIDONTOV, of kvartira 93, ulitsa Marii Ulyanovoi, 11, Moscow, VIKTOR IVANOVICH MOISEEV, of kvartira 74, 3 Mytischinskaya ulitsa, 14-a, Moscow, and LJUBOV PETROVNA KUDESHOVA, of kvartira 391, korpus 2, Studeny proezd, 38, Moscow, all of Union of Soviet Socialist Republics, and all citizens of the Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to devices for converting solar radiation energy into electricity and in particular, to semiconductive photo-voltaic generators that can be used to advantage in solar powerplant designs.

According to one aspect of the present invention there is provided a semiconductor photovoltaic generator comprising a plurality of photovoltaic converters each having a pn junction formed between a substrate and a doped region, the converters being connected in series by current-collecting contacts along opposite planes to form a solid-state structure such that the photo-active face of the generator is of a staircase-like design wherein the area of at least one of the steps is different from the areas of the other steps and the area of each step is inversely proportional to the intensity of incident radiation while the width ("a") of each step is substantially equal to or smaller than the diffusion distance of minority carriers in the substrate.

The problem of increasing the efficiency of the photoactive face and that of raising the photo sensitivity of the generator can be solved by means of providing an additional current-collecting contact placed along the perimeter of each step.

The area of the photo active face and the radiation resistance of the generator can be increased by means of making transverse parallel grooves on the surface of the steps, the space between the crests of adjacent grooves being smaller than the diffusion distance of minority carriers in the substrate, while the p--n junction follows the contour of the steps.

It is expedient that in order to raise the sensitivity of the photo-active face and the radiation resistance of the generator the thickness of the substrate in the photovoltaic converters of the photo-active face is made much smaller than the diffusion distance of minority carriers in the substrate.

It is also expedient that photovoltaic converters are shifted along a respective communication plane (as hereinafter defined) with respect to one another to obtain said staircase-like structure.

An arrangement which is often convenient comprises photovoltaic converters turned through a certain angle with respect to one another about an axis crossing the communication planes (as hereinafter defined) of the photovoltaic converters so as to obtain said staircase-like structures while using an incident radiation flux with concentric distribution of power within the beam.

In case the photovoltaic converters are made as tilted parallelepipeds it is expedient that the edges of the steps have the form of an acute angle while their surfaces are provided with a mirror coating.

An arrangement which is often convenient comprises photovoltaic converters made as similar figures of diminishing sizes placed one behind another to obtain said staircase-type structure.

Preferably said similar figures are represented by either regular polygons, or discs or rings.

According to a further aspect of the invention there is provided a method of fabricating semiconductor photovoltaic generators wherein metal-coated semiconductor plates having p--n junctions along one of their sides are assembled. in a stack, interconnected by means of soldering and compressed simultaneously to squeeze out excessive solder and cut into separate arrays at a certain angle to the plane of the plates, the arrays are then heated until the solder starts melting, at which moment array elements are shifted along the solder layer with respect to one another to obtain said staircase-like structure, a metal coat from the surface of steps obtained in this manner being removed then by an etching procedure.

The invention will be better understood from the following description of embodiments given by way of example with reference to accompanying drawings in which: Fig. 1 presents a semiconductor photovoltaic generator, cross section, with photoactive face made as a staircase-type structure, according to the invention; Figure 2 presents a semiconductor photovoltaic generator as shown in Figure 1 according to the invention, viewed from above; Fig. 3 presents a cross section of a generator of the same design but provided with additional current-collecting contacts, according to the invention Fig. 4 presents a semiconductor photovoltaic generator, partial cross section, wherein grooves are made on the surfaces of steps, according to the invention; Fig. 5 presents a generator as shown in Fig. 4, according to the invention, viewed from above; Fig. 6 presents a generator as shown in Fig. 5, according to the invention, cut along VI-VI; Fig. 7 presents a semiconductor photovoltaic generator wherein the base region is of a variable thickness, according to the invention, cross section; Fig. 8 presents a semiconductor photovoltaic generator having four photoactive faces, according to the invention viewed from above; Fig. 9 presents a generator as shown in Fig. 8 and viewed along arrow A, cross section, according to the invention; Fig. 10 presents a generator as shown in Fig. 8 and viewed along arrow B, cross section according to the invention; Fig. 11 presents a semiconductor photovoltaic generator made as an assembly of plates turned about one axis with respect to one another according to the invention side view; Fig. 12 presents a generator as shown in Fig. 11 viewed from above, according to the invention; Fig. 13 presents a generator as shown in Fig. 12 cut along XIII-XIII, according to the invention; Fig. 14 presents a semiconductor photovoltaic generator wherein the edges of steps in a staircase-type structure are provided with a mirror coating, according to the invention, cross section; Fig. 15 presents a generator as shown in Fig. 14 viewed from above; Fig. 16 presents a semiconductor photovoltaic generator using photovoltaic converters made as similar polygons, according to the invention, viewed from above; Fig. 17 presents a generator as shown in Fig. 16, according to the invention, cut along XVII-XVII; Fig. 18 presents a semiconductor photovoltaic generator using photovoltaic converters made as similar discs, according to the invention, isometric view; Figure 19 presents a generator as shown in Fig. 18, according to the invention, cross section; Fig. 20 presents a semiconductor photovoltaic generaor using photovoltaic converters made as similar rings, according to the invention, cross section; Fig. 21 presents a semiconductor photovoltaic generator at the phase of fabricating a diode structure in the course of production, according to the invention; Fig. 22 presents a generator as shown in Fig. 21 at the phase of assembling diode structures into a stack in the course of production, according to the invention; Fig. 23 presents a generator as shown in Fig. 22 at the phase of shifting photovoltaic converters in the commutation plane in the course of production, according to the invention; Fig. 24 presents a generator as shown in Fig. 23 at the phase after shifting photovoltaic converters in the course of production, according to the invention.

A semiconductor photovoltaic generator comprises photovoltaic converters (1) made as tilted parallelepipeds (Figs. 1, 2) which are interconnected in series and assembled to form a solid-state structure. Every photovoltaic converter 1 in the generator is provided with a pn junction 2 formed between a base region 3 and inverse region 4. Located in the base region 3 is either an isotype p--p+ or n-n+junction 5. The p--n junction 2 or the isotype junction 5 is located in the immediate vicinity of and at a distance not exceeding the diffusion length of the minority carriers in the base region from a photo-active face 6 which receives a flux 7 of incident radiation. The photoactive face 6 is arranged in a staircase-type structure. Every photovoltaic converter 1 is provided with a current-collecting contact 8 attached to the inverse region 4 and with a current-collecting contact 9 attached to the base region 3.

The width "a" of the base of steps 10 whose apex forms an angle ct is about equal to or smaller than, the diffusion distance of minority carriers in the base region 3. The area of every step 10 is inversely proportional to the intensity of the incident radiation flux 7 received by every photovoltaic converter 1. Thus, the area of the steps 10 in the center section of the generator receiving a greater amount of the incident radiation 7 as shown in Fig. 1 is smaller (at the cost of the width "a") than at the periphery of the generator. The thickness "b" of the photovoltaic converter 1 is smaller than the diffusion distance of minority carriers in the base region 3. All the photovoltaic converters 1 have the same length "c" which is of no particular importance. The photovoltaic converters I are wired to one another along their opposite surfaces and each pair of adjacent photovoltaic converters is shifted with respect to each other along a communication plane, by which is meant a plane parallel to the planes of the contact facets of the current collecting contacts for the base and inverse regions of the two adjacent photovoltaic converters.

The generator operates as follows. A flux 7 is incident radiation strikes the st'aircase- type photo-active surface 6 of the generator having a p-n junction 2 or an isotype junction 5 located as aforesaid in the immediate vicinity of the surface 6 and at a distance therefrom not exceeding the diffusion length of the minority carriers in the base region. Thus, current losses caused by surface recombination of light generated carriers are reduced to a minimum.

Additional absorption of the radiation 7 reflected by one of the facets of steps 10 may occur at adjacent facets of nearby steps 10. Thus, reflection losses in the radiation 7 are also reduced, while the area of the photo-active face 6 of the generator is increased.

Variations of the intensity in the incident radiation flux 7 are counter-balanced by respective variations of the area of the photo-active face 6 by means of altering the width "a" of the base of the steps 10 within a specified range (i.e. by means of altering their areas). Thus, the value of the current generated by every photovoltaic converter 1 will be the same throughout the operation surface of the generator.

Power losses due to the in-series resistances will be reduced to a minimum if the width "a" of the base of the steps 10 is made about equal to the diffusion distance of the minority carriers in the base region 3 since almost all the minority-carriers generated by the incident radiation 7 in this case will be collected by the p-n junction 2 located below a continuous current collecting contact 8 for the inverse region 4.

The current-collecting contacts 8, 9 are made of a highly conductive metal which exhibits a negligibly small resistance value.

The value of in-series resistance of the generator can be as small as several thousandths of an Ohm. Thus the generator is able to provide high efficiencies while being illuminated by focused solar radiation, for instance, when located in the focal plane of a linear paraboloid.

The generator will provide high efficiencies while illuminated both from the side of the p--n junction 2 or from the side of the isotype junction 5.

In case the generator is made of silicon typical dimensions of its elements will be as follows: photovoltaic converter thickness "b"-from 0.2 mm to 0.5 mm; step base width "a" from 0.2 to 1.0 mm; photovoltaic converter length "c"-from 5 mm to 50 mm. The depth at which the p-n junction 2 and the isotype junction 5 are buried in the photo-active face 6 is from 0.1 ym to 0.5 fly.

The number of photovoltaic converters per 1 cm2 of the generator's surface is from 10 to 30 pieces, the value of voltage density is from 5 V/cm to 15 V/cm. The thickness of current-collecting contacts is from 5 ,um to 10 ,um.

A generator designed as shown in Fig. 1 will have a larger photo-active face 6 of the photovoltaic converters 1 connected in series, Besides, it will make it possible to match the area of the photo-active face 6 with the power distribution in the incident radiation flux, to reduce power losses in case of non-uniform incident radiation fluxes and to increase the efficiency of the generator in case it receives highly concentrated radiation.

A version of the semiconductor photovoltaic generator presented in Fig. 3 comprises photovoltaic converters 1 each one of which, in addition to a basic current-collecting contact 8 attached to the inverse region 4, is provided with another current-collecting contact 11 connected electrically to the basic contact 8 and arranged along the perimeter of every step 10. The part of the surface of the steps 10 which is free from the current-collecting contact 11 forms a photo-active face 6 of the photovoltaic converters 1. The face 6 receives the radiation flux 7 via a lightguide 12. The lightguide 12 is made as a set of light-conducting elements 13 represented by glass ribbons. The cores of these ribbons have an index of refraction which is higher than that of the surfaces of the ribbons. The ribbons are pressed against each other near the radiation receiving surface 14 and arranged in a fan-like fashion pointing in the direction of the photo-active face 6 of the generator. The -butt-ends of the light-conducting elements 13 are in touch with the photoactive faces 6 of the photovoltaic converters 1 and match them in size.

The current-collecting contacts 9 attached to the base regions 3 are represented by a continuous layer arranged along the isotype junction 5.

The operation of this version of the generator is similar to that of the version shown in Figs. 1 and 2. However, this version makes it possible to improve the effectiveness of the photo-active face 6 and to raise the efficiency of the generator, which is due to the fact that the pn junction 2 collects almost all the current carriers generated by the incident radiation while the spread resistance in the base and inverse regions 3 and 4 is reduced to the minimum. The above, in its turn, is attributed to the fact that the radiation flux 7 is applied to the photo-active face 6 via the lightguide 12 and that the distance between the current-collecting contacts 8, 11 and any point within the volume of the photovoltaic converter, under the photo active face 6, where current carriers are generated is very small and does not exceed the diffusion length of the minority carriers in the base.

The light conducting elements 13 have various values of thickness so that for nonuniform incident radition flux 7 the amounts of power transferred onto corresponding different areas of the photo-active faces 6 will be equal.

Shown in Figs. 4, 5, 6 is still another version of the generator wherein, in contrast to the above version of the photoactive faces 6' of the steps 10 in every photovoltaic converter 1 are provided with transverse parallel grooves 15 having their crests at a space "d" from one another. The space "d" is selected smaller than the diffusion distance of minority carriers in the base region 3 while the p-n junction 2' follows the contour of the surface of the steps 10.

This generator, when compared with the versions shown in Figs. 1 through 3 exhibits a greater area of the photoactive face 6' and makes it possible to absorb the incident radiation flux in a thin subsurface layer located in the immediate vicinity of the p-n junction 2', due to which the minority carrier collection rate is raised and the radiation resistance of the generator is increased. It is expedient that the space "d" between the crests of adjacent grooves is made much smaller than the diffusion distance of minority carriers in the base region 3.

The grooves 15 are made across the steps 10. Thanks to this arrangement the value of the spread resistance in the inverse region 4 is brought down to the required minimum irrespective of the size of the grooves 15, while the efficiency of the generator is increased at high level of incident flux concentration.

Shown in Fig. 7 is still another version of the generator wherein the base region 3' on the surface of the steps 10 in the photovoltaic converters 1 is thinner than the rest of the bulk of the photovoltaic converters 1.

It is expedient that the thickness of the base region 3' is made much smaller than the diffusion distance of minority carriers in the base region 3.

The p-n junction 2 is located on the side opposite to that of the photo-active face 6.

The surface of the inverse region 4 bears a current-collecting contact 8 formed as a continuous layer. In this generator version the photo-active face 6 is treated chemically to reduce the minority carrier surface recombination rate to zero.

Due to the fact that the diffusion distance of minority carriers is initially great and that it is much greater than the thickness of the base region 3' on the steps 10 the above generator version exhibits a high minority carrier collection ratio and an increased value of radiation resistance irrespective of the nature of damaging radiation.

In order to increase the mechanical strength of the outer photovoltaic converter 1 it is connected to the current-collecting contact via an intermediate semiconductor plate 16 having an isotype junction 5 on both sides.

Shown in Figs. 8, 9, 10 is a generator comprising photovoltaic converters 1 made as rectangular parallelepipeds shifted with respect to one another along the communication planes 17. The photo-active face 6 of this generator version comprises steps 10 arranged on four facets of the generator body. The width "a" of each step is the shortest distance on the photo-active face 6 between its face edge and the current collecting contact.

This generator produces twice as much electricity as the device shown in Figs. 1, 2 when illuminated with incident radiation of a similar intensity from four sides, which is due to a layer area of the photo-active face 6.

Shown in Figs. 11, 12, 13 is still another version of the generator comprising photovoltaic converters 1 made as parallelpipeds turned by angle p (in a fan-like fashion) about an axis 18 which crosses the communication planes 17. The width "a" of each step is the average distance from the current-collecting contact to the face edge of the step without a contact.

In this case the photo-active face 6 is also arranged in a staircase-type structure which, however forms a concentric figure having its center on the axis 18. Located in the immediate vicinity of the photo-active face 6 is a p-n junction 2. It is expedient that the angle exceeds 30". This design of the generator appears to be the most optimum since the power distribution in the radiation flux 7 is concentric and the maximum radiation density is at the center located on the axis 18. The value of the spread resistance in the inverse region 4 near the axis 18 is negligibly small. It grows with the distance from the axis 18.

However, the concentration of the radiation flux 7 is reduced too so that the value of the allowable spread resistance is increased respectively.

When compared with the versions shown in Figs. 1 through 10 this generator exhibits higher efficiencies in case of high intensity of the radiation flux with concentric power distribution since the photo-active face forms a concentric figure which is co-axial with the radiation flux.

Shown in Figs. 14, 15 is a generator comprising photovoltaic converters 1 made as tilted parallelpipeds having acute angle steps 10' with apexes forming an angle a.

The photovoltaic converters 1 have p-n junction 2 at their one side and isotype junctions 5 at their other side. Edges 19 of the steps 10 are provided with a mirror coating 20 made, for instance, of aluminium.

The width "a" of the photo-active face 6 of the steps 10' which bears no coating 20 does not exceed the diffusion distance of minority carriers in the base region 3. It is expedient that the angle a does not exceed 30". The radiation flux 7 striking the mirror coating 20 is reflected onto the photo-active faces of adjacent steps 10'. The reflection ratio depends on the incidence angle of the flux 7 and may be from 40% to 95%. In the course of the reflection the radiation flux 7 is absorbed mainly in the regions adjacent to the current-collecting contacts 8 and 9.

Thanks to this arrangement power losses caused by the spread resistance are reduced. At the same time it increases the probability that minority carriers are collected at the p-n junction 2 the distance to which is smaller than the diffusion distance of minority carriers in the base region 3.

When compared with the version shown in Figs. 1, 2 this generator design makes it possible to reduce the reflection losses in case the generator is illuminated with an isotropic radiation flux 7 and to increase the efficiency even in cases of high intensity of the radiaton flux.

A version of the generators shown in Figs, 16, 17 comprises photovoltaic converters 1 made as similar polygon figures, equilateral trapezia in particular, arranged in the order of diminishing size one beyond another to form a photo-active face 6 of staircase-type structure.

The generator comprises six sections 21 arranged symmetrically about a common center, each section being made of photovoltaic converters 1 connected in series.

The sections 21 are secured to one another with the help of dielectric layers 22.

The area of the photo-active face 6 of the photovoltaic converters 1 increases gradually with the distance from the center of the generator due to the increase of the length of the steps 10.

Thanks to this arrangement it becomes possible to bring down power losses when the generator is illuminated with a circular radiation flux 7 wherein the energy concentration maximum is close to its center.

When compared with the version shown in Figs. 11, 12, 13, this generator makes it possible to obtain voltage density per unit area which will be ten or even more times as high.

Shown in Figs. 18, 19 is a generator comprising photovoltaic converters 1 made as discs of similar forms. The photo-active face in this case is formed by ring steps 10.

The area of each step 10 is matched with the concentration value of the circular incidence radiation flux 7.

This design of the generator permits to bring down the spread resistance and to increase the illumination range within which the current and the power continue to be linearly dependent on the intensity of the radiation flux 7.

Shown in Fig. 20 is a generator which comprises photovoltaic converters 1 made as rings similar in form arranged in the order of diminishing size. In this case the photoactive face 6 is represented by a stepped cavity. The base of the generator is formed by a photovoltaic converter 1 made as a disc.

When compared with the design shown in Figs. 18, 19, this generator has a higher efficiency m case it is illuminated with a circular radiation flux 7, since the photoactive face 6 is not shadowed by the current-collecting contacts 8, 9 while the geometry of the steps 10 insures that the generated carriers are collected completely and the power losses due to the series resistance of the generator are brought down.

In the majority of the generator designs according to the invention the currentcollecting contacts occupy no more than 1% of the area of the photo-active face. An increase of the number of photovoltaic converters per unit volume of the generator results in the reduction of the step size and of the value of the series resistance, in the growth of the generated carrier collection ratio, in the reduction of the reflection ratio, in the growth of the generator radiation resistance and in the broadening of the radiation intensity range wherein the values of current and power produced by the generator remain linearly dependent on the intensity of radiation.

The generator shown in Figs. 1, 2 exhibits two-sided photo-sensitivity with practically the same efficiency and can be used as an element of solar power batteries illuminated on both sides.

The concentric generators shown in Figs.

11, 12, 13, 16, 17, 18, 19, 20 exhibit high efficiencies when used in conjunction with optical concentrators made in the form of a body of revolution. They can be employed in attitude control systems as coordinate sensors.

Figs. 21, 22, 23, 24 present a succession of major steps involved in fabricating a semiconductor photovoltaic generator as shown in Figs. 1, 2.

The fabrication procedure, consists of the following phases.

Initial metal-coated semiconductor plates 23 (Fig. 21) having a en junction 2 located along one of the sides of a plate 23 are assembled in a stack as shown in Fig. 22. In the stack the plates 23 are interconnected in series to one another with the use of current-collecting contacts 8, 9 to form a monolithic structure by means of soldering them with the use of a soft solder.

Simultaneously the stack is compressed to squeeze out excessive solder.

Then the stack is cut into separate arrays along planes 24 running at a certain angle with respect to the plane of the plates 23.

The arrays are then placed into a bath 25 (Fig. 23) filled with a liquid having a high boiling point temperature. Using a heater 26 the temperature of the liquid is raised until it reaches that of the solder melting. At this moment a force is applied to the arrays in the direction as shown by arrows 27 in Fig.

23. Yielding to the force the array elements shift with respect to one another along solder layers to match the contour of a staircase-type support 28 fixed to the bottom of the bath 25.

After cooling an array structure is obtained as shown in Fig. 24 which consists of photovoltaic converters 1 shifted in communication planes 17 with respect to one another and provided with a metal coating 29 on the surface of steps 10.

The last phase of the fabrication procedure consists in etching away the metal layer 29. During this phase the surface of the semiconductor material is cleaned completely while the surface of the steps 10 is covered with an anti-reflection coating.

This method of fabricating a generator with a photo-active face of staircase-type structure allows to treat simultaneously a plurality of photovoltaic converters during one production phase and to minimize the amount of required hand labour. Hence, it makes it possible to simplify the procedure of fabricating generators and to increase the productivity.

The method allows to fabricate generators with a photo-active face of a staircase-type structure located on one, two, three or four facets of tfhe generator while selecting the shape of steps applied on both sides of the plates by means of vacuum deposition. Then the silicon plates having a metal coat on both sides were soldered to one another throughout their surfaces using a soft solder to make a stack. Simultaneously the stack was compressed to squeeze out excessive solder.

After that the stack was cut into arrays at a certain angle with respect to the p-n junction planes.

The arrays obtained in this way were then placed into a bath where they were heated up to the melting temperature of the solder.

After that the array elements (photovoltaic converters) were shifted with respect to one another along the solder layer until a staircase structure was formed wherein the width "a" of the steps were equal to the diffusion distance of minority carriers in the base region as shown in Figs. 1, 2.

Then the staircase-type structures were etched in a chemical substance so as to remove the damaged layer from the surface of the semiconductor material as well as to remove metal contacts from the surface of the steps. This process served also to eliminate shunts and to increase the level of photo-activity of illuminated surfaces, Then current collectors were soldered to currentcollecting contacts 8, 9.

The efficiency of this generator appeared to reach 10% with the intensity of the incident radiation flux exceeding 100 W/cm2.

In order to fabricate a semiconductor photovoltaic generator as shown in Fig. 3 the same operations as above are performed. However, prior to subjecting the components to chemical etching the metal contacts along the perimeter of the steps 10 are coated with a chemically resistant film to protect them from the etching substance. Thus, additional currentcollecting contacts 11 are obtained.

A lightguide 12 is made of thin glass ribbons serving as light conducting elements 13 having their butt-ends on one side glued to a photo-active face 6, while the opposite butt-ends are arranged in a pack to form a receiving surface 14. Using a chemical treatment procedure the glass is made to have a lower index of refraction in the subsurface layer.

In order to fabricate a generator as shown in Figs. 4, 5, 6 the same operations are performed as required to fabricate the generator as shown in Figs, 1, 2. However, prior to forming diode structures the silicon plates having their surfaces oriented along < 100 > are etched anisotropically on one side in an alkaline solution to form grooves 15 on the surface of the plates, the direction and pitch of the grooves being preset by a chemically resistant photoresist film that have been applied beforehand.

Another difference of the procedure consists in that the silicon plates are assembled into a stack so that the grooves on all the plates are parallel while the plane 24 along which the stack is cut into arrays lies orthogonally with respect to the grooves 15.

In order to fabricate a generator as shown in Fig. 7 it is necessary to perform the operations required to fabricate the generator as shown in Figs. 1, 2. However, the operation involving' the chemical etching of contacts is followed by an operation involving the chemical etching of silicon on the staircase-type structure bearing the isotype junction 5. The etching will be carried out until the base region 3' on the photo-active face 6 of the photovoltaic converters 1 become several times thinner, i.e. until it is from 10 ,um to 30 pm thick.

In order to fabricate a generator as shown in Figs. 8, 9, 10 it is necessary to perform the operations required to fabricate the generator as shown in Figs. 1, 2. However, the stack is cut into arrays of square elements which are then shifted along the layer of solder in two mutually orthogonal directions.

In order to fabricate a generator as shown in Figs. 11, 12, 13 it is necessary to perform the operations required to fabricate the generator as shown in Figs. 1, 2. However, after the array is trimmed at all its sides to remove shunts the photovoltaic converters 1 will be turned through an angle jB in the commutation planes 17 about the axis 18.

In order to fabricate a generator as shown in Figs. 14, 15 it is necessary to perform the operation required to fabricate the generator as shown in Figs 1, 2. However, the stack will be cut into arrays at a more acute angle to the plane of p-n junctions 2, the surface of the cut will be polished and finally, the edges of the steps will be coated with an aluminium layer of about 0.05 ,um.

The layer will be deposited in vacuum at an angle to serve as a mirror.

In order to fabricate a generator as shown in Figs. 16, 17 it is necessary to perform the operation required to fabricate the generator as shown in Figs. 1, 2. However, the ready device will be scribed into six trapezium shaped sections. The sections then will be interconnected with the help of a dielectric layer 22 to form a hexagon generator.

In order to fabricate a generator as shown in Figs. 18, 19 silicon plates having diode structures and a metal coating will be cut into discs of gradually diminishing diameters. The discs will be soldered in series to form a co-axial stack. In the course of soldering the stack will be compressed to squeeze out excessive solder. The current collecting contacts on external discs will be protected with a chemically resistant film, after which metal contacts from the surface of steps 10 will be chemically etched off.

In order to fabricate a generator as shown in Fig. 20 silicon plates having diode structures and a metal coating will be cut into rings of various diameters.

Simultaneously one disc of the same material will be made with a diameter exceeding those of the rings. The disc will be used as a base for the rings which will be arranged on it co-axially in order of diminishing size and soldered into a stack.

Excessive solder will be removed by means of compressing the stack. Then the currentcollecting contacts on external photovoltaic converters will be protected with a chemically resistant varnish, while the metal contacts on the surface of steps 10 and on the central section of the disc-shaped photo-voltaic converter will be chemically etched off.

WHAT WE CLAIM IS: 1. A semiconductor photovoltaic generator comprising a plurality of photovoltaic converters each having p-n junction formed between a substrate and a doped region, the converters being connected in series by current-collecting contacts along opposite planes to form a solid-state structure such that the photo-active face of the generator is of a staircase-like design wherein the area of at least one of the steps is different from the areas of the other steps and the area of each step is inversely proportional to the intensity of incident radiation while the width ("a") of each step is substantially equal to or smaller than the diffusion distance of minority carriers in the substrate.

2. A semiconductor photovoltaic generator as claimed in Claim 1, wherein an additional current-collecting contact is made along the perimeter of each step.

3. A semiconductor photovoltaic generator as claimed in Claim 1 or 2, wherein transverse parallel grooves are made in the surfaces of steps, the space (d) between the crests of adjacent grooves being smaller than the diffusion distance of minority carriers in the substrate, while the p--n junction follows the contour of the steps.

4. A semiconductor photovoltaic generator as claimed in any one of claims 1 to 3, wherein the thickness of the substrate of the photovoltaic converters when measured from the side of the photo-active face is smaller than the diffusion distance of the minority carriers in the substrate.

5. A semiconductor photovoltaic generator as claimed in any one of claims 1 to 4, wherein the photovoltaic converters are shifted with respect to one another along a respective communication plane (as hereinbefore defined) so as to obtain said staircase-like structure.

6. A method of fabricating semiconductor photovoltaic generators as claimed in claim 5, wherein metal-coated semiconductor plates having p--n junctions along one of their sides are assembled in a stack, interconnected by means of soldering and compressed simultaneously to squeeze out excessive solder and cut into separate arrays at a certain angle to the plane of the plates, the arrays are then heated until the solder starts melting, at which moment array elements are shifted along the solder layer with respect to one another to obtain said staircase-like structure, a metal coat from the surface of steps obtained in this manner being removed then by an etching procedure.

7. A semiconductor photovoltaic generator as claimed in any one of claims 1 to 4, wherein the photovoltaic converters are turned with respect to one another through an angle (ss) about an axis which crosses the communication planes (as hereinbefore defined) of the photovoltaic converters to obtain said staircase-like structure.

8. A semiconductor photovoltaic generator as claimed in claim 5, wherein the photovoltaic converters are made as tilted parallelepipeds, the edges of steps having the form of an acute angle while their surfaces are provided with a mirror coating.

9. A semiconductor photovoltaic generator as claimed in any one of claims 1 to 4, wherein the photovoltaic converters are made as similar figures of diminishing sizes arranged one behind another to obtain said staircase-like structure.

10. A semiconductor photovoltaic generator as claimed in claim 9, wherein said similar figures are represented by regular polygons.

11. A semiconductor photovoltaic generator as claimed in claim 9, wherein said similar figures are represented by discs.

12. A semiconductor photovoltaic generator as claimed in claim 9, wherein said similar figures are represented by rings.

13. A semiconductor photovoltaic generator substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, Figure 3, Figures 4 to 6, Figure 7, Figures 8 to 10, Figures 11 to 13, Figures 14 and 15, Figures 16 and 17, Figures 18 and 19 or Figure 20.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. collecting contacts on external discs will be protected with a chemically resistant film, after which metal contacts from the surface of steps 10 will be chemically etched off. In order to fabricate a generator as shown in Fig. 20 silicon plates having diode structures and a metal coating will be cut into rings of various diameters. Simultaneously one disc of the same material will be made with a diameter exceeding those of the rings. The disc will be used as a base for the rings which will be arranged on it co-axially in order of diminishing size and soldered into a stack. Excessive solder will be removed by means of compressing the stack. Then the currentcollecting contacts on external photovoltaic converters will be protected with a chemically resistant varnish, while the metal contacts on the surface of steps 10 and on the central section of the disc-shaped photo-voltaic converter will be chemically etched off. WHAT WE CLAIM IS:

1. A semiconductor photovoltaic generator comprising a plurality of photovoltaic converters each having p-n junction formed between a substrate and a doped region, the converters being connected in series by current-collecting contacts along opposite planes to form a solid-state structure such that the photo-active face of the generator is of a staircase-like design wherein the area of at least one of the steps is different from the areas of the other steps and the area of each step is inversely proportional to the intensity of incident radiation while the width ("a") of each step is substantially equal to or smaller than the diffusion distance of minority carriers in the substrate.

14. A method of fabricating a semi

conductor photovoltaic generator performed substantially as hereinbefore described, claimed in claim 6 and as shown in Figures 21 to 24. ~~~~~~~~~~~~~~~~~~~~~~