CN1120244A

CN1120244A - Manufacturing technology and using of efficient solar energy conversion to compound photoelectric pol

Info

Publication number: CN1120244A
Application number: CN94107057A
Authority: CN
Inventors: 李国昌; 李果华
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-06-11
Filing date: 1994-06-11
Publication date: 1996-04-10
Anticipated expiration: 2014-06-11
Also published as: CN1044421C

Abstract

The optical composite electrode for efficient conversion of solar energy is made of ZnSe GaAs, YP or Ge in N+-N-P type features its doping concentration is distributed in gradient to form two graded heterojunctions, so having wide response frequency band and high output voltage. Its efficiency is up to 30% when used as electrode of photochemical or photovoltaic solar cell.

Description

High-efficiency solar energy conversion composite photoelectrode, manufacturing process and application thereof

The invention relates to a high-efficiency solar energy conversion composite photoelectrode, a manufacturing process and application thereof, belonging to the technical field of two or more groups of inorganic photoelectric semiconductor materials including AIIBVI, AIIIBV and IV groups.

Since 197The first demonstration of Fujishima and Honda in a photoelectrochemical solar cell using TiO was made in 1 year Japanese₂After the feasibility of photo-electrolysis of water molecules for hydrogen fuel by semiconductor electrodes, a research hot tide has emerged all over the world, but this hot tide begins to cool down to the mid eighties, because one has encountered a difficult difficulty to overcome, namely the contradiction between the energy gap (Eg) of the semiconductor material and the frequency response range of the material, the water molecule decomposition energy being 1.23eV, plus H₂And O₂The required overpotential energy of about 0.7eV for release is only that of wide-gap semiconductors, such as TiO₂GaP, etc. (with energy gaps of 2.95 and 2.25eV, respectively) may be used as photoelectrode, but these materials have red-limited frequencies at the violet end of the solar spectrum, with a frequency response range that covers only a very small fraction (around 5%) of the solar spectrum, so the efficiency of photochemical conversion is deemed to be low, around 1%. In fact, efficiency lower than 8% loses practical value. In order to solve the above-mentioned difficulties, the present inventors proposed to use N-P in a paper entitled research on novel Materials for rasing efficiency of Energy Conversion in PEC Solar Cells, Solar Energy Materials and Solar Cells, 30(1993)61-64, North-Holland) in a paper entitled "research on New Materials for improving Energy Conversion efficiency of photoelectrochemical Solar Cells" to solve the above-mentioned difficulties by selecting a semiconductor material with a smaller Energy gap as a photoelectrode, such as GaAs, whose spectral response curve position is considered to be optimal, but whose output voltage is far from satisfying the thermodynamic and kinetic conditions for decomposing water molecules⁺Three-layer semiconductor composite structure photoelectrodeBy combining a plurality of semiconductor materials with proper energy gaps and close lattice constants, such as ZnSe, GaAs, YP, Ge and the like, the contradiction between wide energy gaps and narrow frequency response ranges, which hinders the development of photoelectrode technology for a long time, is expected to be solved. The idea is a great breakthrough in the technical field of the optical electrode in theory, but because the impurity doping of the P-type semiconductor is technically difficult, the P is the most difficult at present⁺The impurity concentration of the ZnSe semiconductor can only reach 10¹⁷cm^-3From left to right, notThe requirements of the composite photoelectrode can be met, and key technical parameters such as the thickness and the doping concentration of each layer of material and a corresponding manufacturing process are not disclosed in the document, so that the proposal of the assumption does not disclose a complete and practicable technical scheme.

The invention aims to disclose a complete technical scheme of a high-efficiency three-layer semiconductor composite photoelectrode, and also aims to disclose a manufacturing process and application of the composite photoelectrode.

In order to realize the task of the invention, the three-layer structure composite photoelectrode provided by the invention has the advantages that the selection of the semiconductor materials of each functional layer at least comprises two direct transition type materials of GaAs and ZnSe, the semiconductors of each functional layer are gradient doped semiconductors with the doping concentration in gradient distribution, and in addition, the semiconductors of each functional layer are gradient doped semiconductors with the doping concentration in gradient distribution

1. The GaAs is an N-type semiconductor and is used as an intermediate layer of the composite photoelectrode, namely a second functional layer, the thickness of the GaAs is 0.5-3 mu m, and the impurity doping concentration is 1 multiplied by 10¹⁷—1×10¹⁸cm^-3，

2. One of the other two semiconductor materials adjacent to the GaAs is N⁺Type (III) with a doping concentration of 1X 10¹⁰—1×10¹⁹cm^-The other is P type with impurity concentration of 1 × 10¹⁷—1×10¹⁸cm^-3，

3. The impurity doping concentration of three layers of semiconductor materials forming the composite photoelectrode is in a graded gradient relation at an interface to respectively form two heterogeneous graded junctions, one is a P-N junction, and the other is an N-N junction⁺And (6) knotting.

Besides the GaAs and the ZnSe, the third material selected by the invention has two schemes, one scheme is that a direct transition type YP is selected to form a film type composite light electrode with the GaAs and the ZnSe, and the thicknesses of the functional layers at two sides, namely the thickness of the first functional layer and the third functional layer, are 0.3-3 mu m; the other is a substrate which selects indirect transition type Ge as a first functional layer and is also used as a composite photoelectrode, the thickness of the substrate is 0.1-0.5mm, and the thickness of ZnSe as an outer layer, namely a third functional layer, is 0.2-2 mu m.

The key point of the technical scheme is to provideThe optimal selection of the three-layer composite material is realized, the energy gap and the spectral response characteristic of the material are complementary, the lattice matching between the materials is good, and excellent single crystal composite can be formed; the semiconductor type match of the selected material, i.e. N, is also given⁺N-P type thereby avoiding the impurity penetration of high concentration P⁺Difficulty in forming semiconductors; the limit of impurity doping concentration distribution and the thickness of each functional layer can effectively improve the collection rate of photon-generated carriers, reduce the internal resistance of the electrode. The composite photo-electrode has the advantages of high output voltage and wide energy coverage frequency band. When the sunlight irradiates, each functional layer absorbs high-energy, medium-energy and low-energy photons in the sunlight respectively to form respective narrow-peak response curves, and the superposed total response curves can cover the main range of the solar spectrum. According to the sunlight spectrum energy data under the AM1.5 condition, the energy coverage rate of the design is over 90 percent, the sunlight energy can be fully utilized, and the energy conversion efficiency can be improved to about 30 percent.

The manufacturing process of the composite photoelectrode respectively adopts the following two methods according to the difference of transition types of the first functional layer:

when the first functional layer is a direct transition type material such as ZnSe or YP, the process step is to grow Ga about 5 μm thick on a GaAs single crystal wafer substrate_0.3Al_0.7An As buffer layer, and sequentially growing a first functional layer, a second functional layer and a third functional layer; then, a metal electrode with good ohmic contact is arranged on the third functional layer; then immersing the substrate in HF acid corrosive liquid to corrode the buffer layer, so that the substrate and the composite photo-electrode are stripped; the exposed surface of the first functional layer can be plated with metal island layers such as Pt and Ru to prevent the photoelectrode from dissolving. The substrate and buffer layer are of the same type as the first functional layer, and have a nominal doping concentration of 1 × 10¹⁸cm^-3. When the composite photo-electrode with N-GaAs as the substrate grows, the impurity doping concentration of the buffer layer has a gradient transition close to the first functional layer at the junction of the buffer layer and the first functional layer. The stripped substrate can be used for multiple times, so that the manufacturing cost is reduced. The substrate thickness is about 0.3 mm.

When the first functional layer is indirect transition type Ge, the process steps are that GaAs and ZnSe of a second functional layer and a third functional layer are directly and sequentially grown on a substrate Ge with the thickness of 0.1-0.5 mm; then, arranging a metal electrode with good ohmic contact on the exposed surface of the substrate Ge; the light irradiation surface of the third functional layer can be plated with a metal island layer such as Pt, Ru and the like. The crystal growth technique can adopt one of the following techniques: vapor Phase Epitaxy (VPE), Liquid Phase Epitaxy (LPE), and Metal Organic Chemical Vapor Deposition (MOCVD).

The composite photoelectrode is used for a photoelectrochemical solar cell, can overcome the fatal weakness that the frequency response range and the output voltage of the existing photoelectrochemical solar cell can not be considered at the same time, and improves the energy conversion efficiency of obtaining hydrogen fuel by decomposing water by using solar energy to about 30 percent; the high-efficiency high-output-voltage photochemical solar cell can also be used for degrading macromolecules in sewage.

The composite photoelectrode can also be directly used for a photovoltaic solar cell, so that the photoelectric conversion efficiency of about 15 percent in the prior art is improved to about 30 percent.

The present invention will be described in detail with reference to the accompanying drawings and examples.

FIG. 1-FIG. 4 are four direct transition type thin film composite photo-electrode structures.

Fig. 5 is a graph of doping concentration.

FIG. 6 shows the structure of the thin film electrode after peeling.

Fig. 7 and 8 show two composite photo-electrode structures using Ge as a substrate.

Fig. 9 is a graph of the spectral response curves of four selected functional semiconductor materials according to the present invention and the relative wavelength position of the solar spectrum under AM 1.5.

FIG. 10 is a graph of a dual-layer composite photoelectrode structure for verification and the corresponding impurity concentration profile.

Fig. 11 is a graph of the spectral response of this experiment.

Fig. 12 and 13 are schematic diagrams showing the operation of the composite photoelectrode in a non-illuminated state and in an illuminated state, respectively, when the composite photoelectrode is used to form a photochemical solar cell.

Fig. 14 is a view showing the structure of a photovoltaic solar cell.

Fig. 15 is a structural view of an actinic solar cell.

Four composite photoelectrode shown in figures 1-4, three functional layers of which adopt direct transitionYP, GaAs and ZnSe as type materials, arranged in order of growth and P-N⁺Combinations of semiconductor types coexist in four configurations. Respectively is the first N (figure 1) according to growth order⁺-ZnSe, N-GaAs, P-YP, second (FIG. 2) P-ZnSe, N-GaAs, N⁺P, third (FIG. 3) N⁺-YP, N-GaAs, PZnSe, fourth (FIG. 4) P-YP, N-GaAs, N⁺-ZnSe. Wherein the thickness of the first functional layer and the second functional layer is 0.5-3 μm, and the total thickness of the three functional layers is 3-9 μm. In the manufacturing process, the four electrodes all use GaAs as a substrate, the thickness of the substrate is about 0.3mm, and a layer of Ga with the thickness of about 5 mu m is grown on the substrate_0.3Al_0.7An As buffer layer 2, and then three

functional layers

3, 4 and 5 are sequentially grown. The substrate and buffer layer are of the same type as the first functional layer 3, e.g. the first functional layer 3 is N in fig. 1⁺ZnSe, then substrate 1 is N-GaAs and buffer layer 2 is N-Ga_0.3Al_0.7As。

The doping concentration profile of each layer of material is shown in fig. 5. The solid line in the figure represents the doping concentration profile of the example shown in fig. 1 and the dashed line represents the doping concentration profile of the example shown in fig. 2. When the substrate 1 is N-GaAs, the impurity doping concentration of the substrate 1 and the buffer layer 2 is from 1 × 10¹⁹cm^-3Initially, near the first functional layer 3, its doping concentration has a direction 10¹⁴cm^-3This transition control need not be very strict since the buffer layer 2 is not a functional layer. The doping concentrations of the three

functional layers

34 and 5 from the first functional layer 3 are controlled in a gradient relationship such that the semiconductor of each functional layer becomes a gradient doped semiconductor and a heterojunction is formed at the interface of the adjacent functional layers. The curves in the figure are schematic, the actual gradient profile is a staircase, and the whole doping process is controlled by a computer. Since the photogenerated carriers require the action of the junction electric field to actually contribute to the photoelectric conversion, in other words, the main photoelectric conversion effect is the junction electric field occurring in the semiconductor orThe gradient doped semiconductor material is required to be selected near the junction electric field, and a heterogeneous graded junction is formed between the functional layers, so that the junction electric field and an influence area thereof are expanded to the whole functional layer, and the collection rate of photon-generated carriers is improved.

The buffer layer 2 is a material which is easy to be corroded by hydrofluoric acid, and is a material with a lattice constant close to that of the selected substrate material YP and the selected functional layer material ZnSe, when the growth of the

functional layers

3, 4 and 5 is finished, the composite material can be immersed into a corrosive liquid together to corrode the buffer layer 2, so that the upper functional layer is stripped from the substrate 1, and the GaAs lining plate with high price can be used for multiple times.

Considering that the thickness of the peeled functional layer is too thin, not more than 10 μm, the strength is low, and the operability is poor during reprocessing, the actual manufacturing process is to evaporate an Al-Ag thin layer on the exposed surface of the third functional layer 5 after the functional layer crystal growth is finished, then to set the metal electrode 6 with good ohmic contact, then to coat paraffin on the surface, and then to etch with HF, to form the composite photoelectrode shown in fig. 6. Finally, a metal island layer such as Pt Ru can be plated on the light irradiation surface.

Fig. 7 and 8 exemplify two kinds of first functional layers 7 using indirect transition type Ge sheets with a thickness of 0.1 to 0.5mm as substrates, on which second and third functional layers 8 and 9 are sequentially grown, the thickness of the second functional layer 8 being 0.5 to 3 μm, and the thickness of the third functional layer 9 being 0.2 to 2 μm. This composite photo-electrode does not need to be peeled off, and a metal electrode with good ohmic contact is directly arranged on the exposed surface of the first functional layer 7, and the exposed surface of the third functional layer 9 is used as a light irradiation surface. The second functional layer 8 of the two composite photoelectrodes still adopts a direct transition type N-GaAs gradient material. The third functional layer is direct transition type ZnSe, the type of which is still two and selects N⁺And P-type. When using N⁺-ZnSe the first functional layer 7 is P-Ge as shown in fig. 7; the first functional layer 7 is N when P-ZnSe is used⁺Ge, as shown in fig. 8, still forming a heterograded junction between adjacent functional layers. Similarly, the light-irradiated surface can be plated with metal island layers of Pt, Ru and the like to protect the composite material.

The crystal growth may be carried out by one of the following techniques, Vapor Phase Epitaxy (VPE), Liquid Phase Epitaxy (LPE), or Metal Organic Chemical Vapor Deposition (MOCVD).

The six composite photo-electrodes listed above relate to five semiconductor materials, and some of the most important properties are listed in table 1:

TABLE 1

Semiconductor device and method for manufacturing the same	Energy gap (eV)	Crystal constant	Transition type	Crystal structure
Semiconductor device and method for manufacturing the same	Energy gap (eV)	Crystal constant	Transition type	Crystal structure	Ge	0.67	5.657	Indirect connection	Diamond
YP	1.00	5.652	Direct connection	Sphalerite ore	Ge	0.67	5.657	Indirect connection	Diamond
YP	1.00	5.652	Direct connection	Sphalerite ore	GaAs	1.43	5.653	Direct connection	Sphalerite ore
ZnSe	2.58	5.669	Direct connection	Sphalerite ore	GaAs	1.43	5.653	Direct connection	Sphalerite ore
ZnSe	2.58	5.669	Direct connection	Sphalerite ore	Ga_0.3Al_0.7As		5.653	Indirect connection	Sphalerite ore

As can be seen from Table 1, the lattice constants of these materials are very close, and this property lays a good foundation for the growth of heterogeneous single crystals. However, 0.28% of lattice mismatch exists between GaAs and ZnSe, and one way to narrow the difference in lattice constant between them is to dope S in ZnSe. As S and Se are same elements and have slightly smaller atomic radius, the lattice constant of the doped crystal ZnSe is reduced compared with the ZnSe not doped with S. Thus, excellent heterogeneous single crystals can be obtained no matter ZnSe is grown on GaAs or GaAs is grown on ZnSe.

The relationship between the red limit wavelength position and the relative wavelength position of the sun and the spectrum corresponding to the energy gaps of the four functional semiconductor materials is shown in fig. 9. The selected materials form respective narrow peak response curves after absorbing different energy photons in sunlight, although the respective narrow peak response curves can not cover the whole solar spectrum, the superposed total response curves can cover the main range of the solar spectrum, and according to the sunlight spectrum energy data under the AM1.5 condition, the energy coverage rate of the design is over 90 percent, the energy can be fully utilized, and the energy conversion efficiency can be greatly improved to 30 percent. Left and right

The photoelectrode is formed by adopting a composite semiconductor material, and aims to improve the open-circuit photovoltage of the photoelectrode and widen the spectral response curve of the photoelectrode. To confirm two characteristics of the composite photoelectrode, we only use a N-GaAs photoelectrode with one layer and a photoelectrode with two functional layers, namely N-GaAs/P-Ga_0.8Al_0.7As test comparison, the structure and corresponding doping concentration curve of the two-layer composite photoelectrode for experiment are shown in FIG. 10, in which the photoelectrode is composed of a substrate 10, N-GaAs, 0.3mm, a buffer layer 11, N-GaAs, 0.5mm, a first functional layer 12, N-GaAs, 2mm, a heterojunction 13,500 13,500 Å, a second functional layer 14, and P-Ga from the bottom_0.8Al_O.2As, 0.5 μm doping concentration from 10 starting from the first functional layer 12¹⁸cm^-3. Decreases in a gradient to a heterojunction 13 of 10¹⁷cm^-3Then in a gradient up to 10 in the second functional layer 14¹⁸cm^-3The electrode is grown using MOCVD techniques. Actually measuring the double-layer compositionThe open-circuit photovoltage of the photoelectrode is 0.6394V, the open-circuit photovoltage of the single-layer N-GaAs of the control group is 0.1789V, the photovoltage increment is 0.46V, and the value is matched with the energy gap difference of 0.47ev between the two materials used by the composite photoelectrode (Ga_0.8Al_0.2Eg of As 1.90eV and Eg of GaAs 1.43 eV). This fact indicates that as a result of the work of the diffusion force on the photogenerated carriers, the electron-hole photogenerated carriers with lower energy photophobia in the composite photoelectrode are energized to the photogenerated carriers with higher energy difference, in other words, the open circuit photovoltage of the composite photoelectrode is determined by the largest one of the energy gap values in the material constituting the electrode.

Fig. 11 shows the spectral response characteristic curves of the composite photoelectrode for the experiment and the control group, and the SRC curve of the composite photoelectrode is already obviously broadened.

The working mechanism of the composite photoelectrode in a photoelectrochemical solar cell is described below with reference to fig. 12 and 13. Fig. 12 is a graph showing the energy relationship between the photo-electrochemical solar cell in a non-light-balanced state, and fig. 13 is a graph showing the energy relationship between the photo-electrochemical solar cell in a non-light-balanced state. In the figure, P-YP, N-GaAs and N⁺-ZnSe constitutes the three

functional layers

5, 4 and 3 of the composite photoelectrode, metal 6 as the electrode of the composite photoelectrode and Pt electrode 20 as the cathode of the solar cell. Under the condition of no illumination, the diffusion of majority carriers in each functional layer of the composite photoelectrode acts on two heterogeneous graded junctions P-N junction 21 and N-N junction⁺Junction 22 establishes a junction electric field that blocks the majority carriers from continuing to diffuse. The diffusion force equals the electric field force when the system reaches equilibrium. Similarly, band bending is formed also at the interface between the semiconductor functional layer 3 and the electrolyte 23 and at the interface between the functional layer 5 and the metal electrode 6, and band bending is very significant at the solid-liquid surface. In the figure, Ef is the fermi level and Vfb is the flat band potential.

When the light irradiates, photon-generated carriers generated by the composite functional layer, namely non-equilibrium carriers, are separated by two series-connected heterogeneous slowly-varying junction electric fields, photon-generated electrons move to the right and are accumulated on the right of the junction electric field, and photon-generated holes move to the left and are accumulated on the left of the junction electric field. Due to the obstruction of the Schottky barrier on the solid-liquid interface, the accumulation of the carriers in the non-equilibrium state is equivalent to adding bias to two heterogeneous graded junctionsAnd the balance established in the absence of illumination is broken, and under the action of diffusion force, most carriers flow up again, electrons flow from right to left, and holes flow from left to right. A photocurrent I participating in the photoelectrochemical reaction is formed when the loop is closed. The energy photophobia between the output electrons and holes is approximately equal to the maximum energy gap value of the composite photoelectrode, namely the Eg of ZnSe: 2.58eV, H₂/H₂O and OH^-/O₂Has an energy level difference of 1.23eV, and is in direct contact with N in the solution⁺The flat band potential Vfb of the type ZnSe is 0.28 Vvs. SCE (IN KCD, which is greater than H)₂/H₂O level, -0.49Vvs. SCE, lower, and therefore level H₂/H₂O and OH^-/O₂Just falls in the middle of the forbidden band of ZnSe, so that the cavity energy automatically flows to OH with lower energy^-/H₂O, realizing photoelectrochemical decomposition of water, adjusting the absolute positions of the flat band potentials of the electrodes by changing the types of solutions and the concentrations of solutes, and enabling the energy level positions to be in the optimal matching state so as to ensure that the requirements of photochemical reactions are completely met under different specific conditionsThermodynamic and kinetic conditions. In the drawings_nE_f ⁺、_pE_f ⁺Are the quasi-fermi levels of electrons and holes.

The following is a schematic structural diagram of a photovoltaic solar cell and an actinic solar cell which are made of the composite photoelectrode.

In FIG. 14, the thin film type electrode N is used⁺ZnSe, N-GaAs, P-YP are taken as an example to illustrate the structure of the photovoltaic solar cell. The P-YP layer of the composite photo-electrode 30 is in good ohmic contact with the copper sheet 32 through the Al-Ag evaporation layer 31, and the metal sheet 32 is led out of the shell and serves as the positive electrode of the photovoltaic cell. On the illuminated surface N of the composite photo-electrode 30^-On the exposed surface of the-ZnSe is provided a grid electrode 33 as the negative electrode of the cell, in the middle of the grid is an antireflection film layer 34, and at the uppermost end of the case 32 is a glass plate 35. The efficiency of the photovoltaic solar cell can be improved by about 1 time compared with the photovoltaic cell using single-layer GaAs.

FIG. 15 again taken as P-YP, N-GaAs, N^-The ZnSe composite photoelectrode exemplifies the structure of the photochemical solar cell, where the lower metal sheet 32 of the composite photoelectrode 30 is Pt or Ni material as lightThe cathode of the battery is plated with a metal island layer protective layer 37 on the upper illumination surface, and the periphery of the electrode is sealed and protected by epoxy resin 36. The upper electrolyte solution 38 is the anode region, which occurs at the electrode The oxidation reaction takes place on the metal sheet 32 with the lower electrolyte solution 39 as the cathode region The reaction is also thick. O is₂And H₂And the electrolyte is collected and discharged through the right end and the left end of the upper part of the shell respectively, and a salt bridge membrane 40 is arranged at the junction of the upper electrolyte solution and the lower electrolyte solution and is used as an isolating membrane of the cathode and the anode of the photovoltaic cell.

Claims

1. The efficient solar energy conversion composite photoelectrode consists of three layers of composite semiconductor single crystal materials, and is characterized in that the three layers of semiconductor materials at least comprise two direct transition type materials of GaAs and ZnSe, and all the functional semiconductor materials are gradient doped semiconductors, and

(1) the GaAs is N type, is used as the intermediate layer of the composite photoelectrode, has the thickness of 0.5-3 mu m and the doping concentration of 1 multiplied by 10¹⁷-1×10¹⁸cm^-3，

(2) Two other semiconductor materials adjacent to GaAs, one being N⁺Type (III) with a doping concentration of 1X 10¹⁸—1×10¹⁹cm^-3The other is P type with the impurity concentration of 1 × 10¹⁷－1×10⁴cm^-3，

(3) The doping concentrations of three layers of semiconductor materials forming the composite photoelectrode are in a graded gradient relationship at the mutual joint interface, two heterogeneous graded junctions are respectively formed, one is a P-N junction, and the other is an N-N junction⁺And (6) knotting.

2. The efficient solar energy conversion composite photoelectrode as claimed in claim 1, wherein the third semiconductor material of the composite photoelectrode is a direct transition type YP, and forms a thin film type composite photoelectrode with the GaAs and the ZnSe, and the thickness of the functional layers on the two sides of the thin film type composite photoelectrode is 0.3-3 μm respectively.

3. A high efficiency solar energy conversion composite photoelectrode as claimed in claim 2 wherein the total thickness of the three functional layers of said composite photoelectrode is greater than 3 μm.

4. A high efficiency solar energy conversion composite photoelectrode as claimed in claim 2 or 3 wherein said ZnSe material is doped with element S.

5. The efficient solar energy conversion composite photoelectrode as claimed in claim 1, wherein the third semiconductor material of said composite photoelectrode is indirect transition type Ge, which doubles as a substrate of the electrode, and the thickness thereof is 0.1-0.5mm, and said ZnSe is an outer functional layer, and the thickness thereof is 0.2-2 μm.

6. An efficient solar energy conversion composite photoelectrode as defined in claim 5 wherein said ZnSe material is doped with an element S.

7. A process for preparing an efficient solar energy conversion composite photoelectrode as claimed in claim 1, wherein GaAs is used as substrate, a buffer layer is grown on the substrate by single crystal growth method, then functional layers composed of ZnSe, GaAs and YP are grown in sequence, said buffer layer is Ga_0.3Al_0.7As, nominal doping concentrations of substrate and buffer layer are 1X 10¹⁸cm^-3Which are of the same type P or N as the first functional layer adjacent to the buffer layer, the nominal thickness of the buffer layer being 5 μm and the nominal thickness of the substrate being 0.3mm, and finally the functional layer being stripped from the substrate by etching the buffer layer with hydrofluoric acid.

8. An efficient solar energy conversion composite photoelectrode as claimed in claim 7 wherein a good ohmic contact sheet metal is provided after deposition of an Al-Ag layer on the exposed surface of the outer functional layer of the composite photoelectrode prior to the lift-off process.

9. An efficient solar energy conversion composite optoelectrode as claimed in claim 7 or 8, wherein the composite optode is a composite optodeThe first functional layer of the electrode is N⁺When the crystal is in a type, the crystal of the buffer layer grows in the area adjacent to the first functional layer, and the doping concentration of the crystal is controlled to be 1 multiplied by 10¹³To 1X 10¹⁹cm^-3And (6) transition.

10. A process for fabricating an efficient solar composite photoelectrode as claimed in claim 1 wherein Ge is used as a substrate, a second functional layer GaAs and a third functional layer ZnSe are grown thereon in sequence by a single crystal growth process, and then a metal sheet with good ohmic contact is provided on the exposed surface of said substrate.

11. A high efficiency solar composite photoelectrode as claimed in claim 1 which is an electrode for a photoelectrochemical solar cell or a photovoltaic solar cell.