A three-terminal three-junction perovskite / gallium arsenide photovoltaic cell and a method of making the same
By introducing a transparent conductive intermediate layer into the photovoltaic cell, optical coupling and electrical isolation between the perovskite top cell and the III-V double-junction cell are achieved, solving the problems of complexity and high loss in the fabrication of traditional multi-junction cells, and realizing efficient and flexible three-terminal triple-junction photovoltaic cell integration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI LONGYU XINHANG ENERGY TECHNOLOGY CO LTD
- Filing Date
- 2026-04-18
- Publication Date
- 2026-07-31
AI Technical Summary
Traditional multi-junction photovoltaic cells suffer from problems such as complex tunneling junctions, high current matching requirements, limited material selection, and large optical and electrical losses during the fabrication process, making it difficult to achieve the integration of high-efficiency III-V group multi-junction cells and perovskite cells.
A three-terminal, three-junction photovoltaic cell structure is adopted. By introducing a transparent conductive intermediate layer as a functional intermediate electrode, optical coupling and electrical isolation between the perovskite top cell and the lower III-V double-junction cell are achieved, simplifying the fabrication process and reducing tunneling junctions. The cell structure is fabricated using a bottom-to-top step-integration method.
It reduces tunnel junction losses, simplifies epitaxial structure, lowers series resistance and voltage drop, improves carrier collection efficiency, enhances process flexibility and optical integration, and achieves high-efficiency photovoltaic cell performance.
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Figure CN122497215A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photovoltaic cell technology, specifically to a high-efficiency multi-junction solar cell structure and its fabrication method, and in particular to a perovskite / gallium arsenide / indium gallium arsenide triple-junction photovoltaic cell with a three-terminal electrode design. Background Technology
[0002] The efficiency of photovoltaic cells is limited by the finite absorption of the solar spectrum by a single semiconductor material. Multi-junction cells, by stacking materials with different band gaps, achieve segmented absorption of the solar spectrum, which is the main approach to breaking through the efficiency limit. However, traditional monolithic multi-junction cells require each sub-cell to be connected in series through tunneling junctions, which necessitates the fabrication of complex and high-quality heavily doped tunneling junctions and introduces additional optical and electrical losses. At the same time, the series structure requires strict current matching among the sub-cells, limiting the flexibility of material selection and spectral utilization.
[0003] To circumvent tunneling junction and current matching issues, multi-terminal (multi-junction) cell structures have been proposed. These structures electrically isolate different sub-cells, leading them out through independent electrodes, thus avoiding direct series connection between sub-cells. However, existing multi-terminal devices often employ lateral wiring or complex etching isolation processes, increasing fabrication difficulty and dead area, and making it difficult to achieve high-quality integration of ultra-thin, high-efficiency III-V group multi-junction cells with emerging perovskite cells. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a compact, low-loss, and flexible three-terminal triple-junction photovoltaic cell and its fabrication method. The core concept of this invention lies in: by introducing a planarized transparent conductive intermediate layer as a functional intermediate electrode, optical coupling and electrical isolation between the perovskite top cell and the underlying III-V group (gallium arsenide / indium gallium arsenide) double-junction cell are cleverly achieved.
[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A three-terminal, three-junction photovoltaic cell is characterized by its unique interlayer positioning and connection: along the light incidence direction, a perovskite top cell, a transparent conductive layer serving as the intermediate electrode, a gallium arsenide intermediate cell, a tunnel junction, and an indium gallium arsenide bottom cell are stacked vertically in sequence. The transparent conductive layer physically contacts the bottom functional layer (such as the electron transport layer) of the perovskite top cell and the top contact layer of the gallium arsenide intermediate cell, while electrically serving as an independent electrode port. This design allows the charge carriers generated by the top cell and those generated by the intermediate / bottom cells to be collected separately through different electrodes (front electrode / intermediate electrode / back electrode), forming a three-terminal output.
[0006] More specifically, the gallium arsenide intermediate cell and the indium gallium arsenide bottom cell are first epitaxially grown into a single structure on the original substrate, and then transferred to a supporting substrate through sacrificial layer peeling and bonding. Subsequently, an intermediate electrode is fabricated on the surface of the transferred III-V double-junction cell, and finally, a perovskite top cell is fabricated on it. This "bottom-up, step-by-step integration" fabrication sequence is the key to achieving the aforementioned complex structure in this invention.
[0007] The beneficial effects of this invention are as follows: Structural innovation reduces losses: Compared with traditional triple-junction series cells that require two tunnel junctions, this invention only retains one tunnel junction between the middle cell and the bottom cell, fundamentally reducing one high-loss tunnel junction, simplifying the epitaxial structure, and reducing series resistance and voltage loss.
[0008] Highly efficient collection and optimized path: The introduction of the intermediate electrode allows the carriers of the top and bottom cells to be collected by the near-end electrode without having to traverse the entire stack, which significantly shortens the lateral transport path of the carriers, reduces recombination losses, and helps to improve the fill factor.
[0009] Process decoupling and high flexibility: The fabrication of III-V group solar cells and perovskite solar cells are completed in independent process steps, avoiding the process incompatibility issues between the two types of materials in terms of growth temperature and chemical environment. The fabrication and modification of intermediate electrodes can be carried out independently, providing additional degrees of freedom for performance optimization.
[0010] High optical integration: The planar transparent intermediate electrode replaces the traditional etched isolation trench, minimizing the loss of photosensitive area and ensuring a high optical fill factor for the device. Attached Figure Description
[0011] Figure 1 This is a schematic cross-sectional view of the overall structure of a three-terminal, three-junction photovoltaic cell provided in an embodiment of the present invention.
[0012] Figure 2 yes Figure 1 A schematic diagram of the refined layered structure of a perovskite top solar cell (103).
[0013] Figure 3 yes Figure 1 A schematic diagram of the refined layered structure of a gallium arsenide intermediate cell (105).
[0014] Figure 4 yes Figure 1 A schematic diagram of the refined layered structure of the indium gallium arsenide bottom cell (107).
[0015] Figure 5 This is a schematic diagram of the initial structure after epitaxial growth of III-V group materials on the original substrate in the preparation method of the present invention.
[0016] Figure 6 yes Figure 5 The Bragg reflector structure shown in section 1075.
[0017] Figure 7 yes Figure 5 The diagram shows a cross-sectional view of the independent III-V double-junction thin film obtained after removing the sacrificial layer and the original substrate. The structure includes an intermediate cell (105), a tunnel junction (106), a bottom cell (107), a back metal layer (108), and a supporting substrate (109).
[0018] Figure 8 yes Figure 7 The diagram shows the structure after the intermediate electrode unit is fabricated on the 1051 surface, including a top view and a cross-sectional view of the unit.
[0019] Figure 9 This is a schematic cross-sectional view of the complete structure of the three-terminal, three-junction photovoltaic cell of the present invention. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the implementation methods of the technical solutions of this invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following description is intended to illustrate the implementation process of this invention, and not to limit the scope of protection of this invention.
[0021] First embodiment: The complete structure of a three-terminal, three-junction photovoltaic cell: Figure 1 The overall cross-sectional structure of the three-terminal, three-junction photovoltaic cell provided in this embodiment is shown. The positions, connections, and mating relationships of this structure along the light incident direction from top to bottom are as follows: Front gate electrode (101): Located on the top layer of the device, it is used to collect holes generated by the perovskite top cell (taking the polarity of this embodiment as an example). It is typically designed as a fine grid line to minimize optical obstruction.
[0022] Antireflection layer (102): Covers the front gate electrode (101) and the exposed perovskite cell surface to reduce the reflection loss of incident light. In this embodiment, an NbO2 / SiNx composite film is used.
[0023] Perovskite top solar cell (103): As a top solar cell, it is responsible for absorbing high-energy, short-wavelength photons. Its detailed layered structure is shown below. Figure 2 As shown: Hole transport layer (1031, HTL): Located on the top layer, made of NiOx, used to selectively extract and transport holes to the front gate electrode (101).
[0024] Perovskite absorption layer (1032): FA-based perovskite (FaPbIxBr3-x) is used as the core light absorption layer.
[0025] Electron transport layer (1033, ETL): Located at the bottom layer, made of SnO2, it is used to selectively extract and transport electrons. Its lower surface forms an ohmic contact directly with the subsequent intermediate electrode unit (104), which is the key connection point for achieving independent output of the top cell current.
[0026] Intermediate electrode unit (104): This layer is one of the core innovations of this invention, serving as an independent intermediate electrode. It performs two main functions simultaneously: Electrical function: As a common electrode, it collects electrons from the perovskite top cell (103) on the one hand, and from the gallium arsenide intermediate cell (105) below on the other hand.
[0027] Optical function: As an optical coupling layer, it allows long-wavelength photons not absorbed by the top cell to transmit to the lower cell. This embodiment uses ITO (indium tin oxide) and optimizes its work function by adjusting the oxygen content.
[0028] Gallium arsenide intermediate cell (105): Responsible for absorbing mid-wavelength photons. Its structure is as follows: Figure 3 As shown, from top to bottom, it includes: The front contact layer (1051) is n⁺-GaAs, which forms a good ohmic contact with the transparent conductive film (104) above, ensuring that the electrons of the intermediate cell can be effectively collected by the intermediate electrode.
[0029] Front window layer (1052): n-AlInGaP, which provides surface passivation and allows light to pass through.
[0030] Absorption layer (1053): n-GaAs, core absorption region.
[0031] Back window layer (1054): p-AlGaAs.
[0032] Back contact layer (1055): p⁺-GaAs, which forms a connection with the tunnel junction (106).
[0033] Tunneling junction (106): A heavily doped p⁺⁺ / n⁺⁺ junction (such as p⁺⁺-AlGaAs / n⁺⁺-InGaAs) connecting the intermediate cell (105) and the bottom cell (107) to achieve carrier tunneling. In the three-terminal structure of this invention, only this tunneling junction is required, which is less than that of a conventional three-junction series cell.
[0034] Indium gallium arsenide (IGaAs) bottom cell (107): responsible for absorbing low-energy, long-wavelength infrared photons. Its structure is as follows... Figure 4 As shown, it includes: Lattice buffer layer (1071): InGaP with a gradient composition, used to adapt to the lattice constants of the upper and lower layers and to avoid parasitic absorption.
[0035] Front contact layer (1072): n⁺-InGaAs.
[0036] Front window layer (1073): n-InGaP.
[0037] Absorbing layer (1074): p-InGaAs.
[0038] Distributed Bragg reflector (1075, DBR): A multilayer film composed of alternating stacks of InGaAs (10751) and AlInP (10752) that reflects long-wavelength photons transmitted to the bottom back to the absorption layer for secondary absorption.
[0039] Back contact layer (1076): p⁺-InGaAs.
[0040] Back electrode (108): Located at the bottom of the device, it is usually made of a whole surface of metal (such as Ag) and is used to collect holes generated by the bottom cell (107) and the middle cell (105).
[0041] Support structure (109): Any type of support substrate Key coordination relationships summary: In this embodiment, the front gate electrode (101) and the back electrode (108) have the same polarity (both are positive), while the transparent conductive film (104) serves as the intermediate electrode and is the negative electrode. The charge carriers (electrons downward, holes upward) generated by the perovskite top cell (103) and the charge carriers (electrons upward, holes downward) generated by the gallium arsenide / indium gallium arsenide dual-junction cells (105, 107) are completely separated in the spatial transport path, and are finally output independently through three ports, realizing an innovative architecture of optical stacked series and electrical parallel / independent management.
[0042] Second embodiment: Detailed preparation method of three-terminal triple-junction photovoltaic cell This embodiment details the battery fabrication process in the first embodiment, focusing on the process sequence and structural coordination of each module. Figures 5 to 9 The device form after the key steps are shown.
[0043] Step 1: Epitaxial growth and initial structure preparation of III-V double-junction solar cells (corresponding to...) Figure 5 ) A raw gallium arsenide (GaAs) substrate (201) is provided.
[0044] The following layers were epitaxially grown sequentially using metal-organic chemical vapor deposition (MOCVD) technology: Buffer layer (202): A GaAs layer is grown to improve the surface morphology of the substrate.
[0045] Sacrificial layer (203): An AlAs layer is grown, which has a high etch selectivity with the adjacent layer, in preparation for subsequent stripping.
[0046] Intermediate cell structure (105): n⁺-GaAs front contact layer (1051), n-AlInGaP front window layer (1052), n-GaAs absorption layer (1053), p-AlGaAs back window layer (1054), and p⁺-GaAs back contact layer (1055) are grown sequentially.
[0047] Tunnel junction structure (106): p⁺⁺-AlGaAs layer (1061) and n⁺⁺-AlGaAs layer (1062) are grown.
[0048] The bottom cell structure (107) consists of an InGaP lattice buffer layer (1071) with gradually varying composition, an n⁺-InGaAs front contact layer (1072), an n-InGaP front window layer (1073), a p-InGaAs absorption layer (1074), a DBR anti-reflection layer (1075) composed of InGaAs (65nm) / AlInP (82nm) pairs, and a p⁺-InGaAs back contact layer (1076).
[0049] Step 2: Substrate transfer and release of III-V thin films (corresponding to...) Figure 6 and Figure 7 (Note the distinction) Fabricate and bond the back electrode, and peel off the original substrate (corresponding to...). Figure 7 On the surface of the epitaxially completed bottom cell structure (107) (i.e., on the back contact layer 1076), a silver (Ag) back electrode (108) is prepared by physical vapor deposition. Subsequently, a support substrate (109) is bonded to the back electrode (108) to provide support. The bonded sample is then immersed in a hydrofluoric acid (HF) solution to selectively etch the AlAs sacrificial layer (203). After the sacrificial layer is completely etched, the original substrate (201) and the buffer layer (202) are removed, thereby obtaining an independently supported III-V double-junction film consisting of an intermediate cell (105), a tunnel junction (106), and a bottom cell (107). At this time, the surface of the front contact layer (1051) of the intermediate cell is exposed.
[0050] Step 3: Fabrication of the intermediate electrode unit (104) (corresponding to) Figure 8 ) Silver (Ag) grid electrodes (1041) are fabricated on the exposed surface of the intermediate cell structure (1051) by screen printing or inkjet printing.
[0051] Using a magnetron sputtering process, an indium tin oxide (ITO) thin film is deposited to form a transparent conductive film (1042) covering the entire grid line and the surface of the cell. The silver grid line (1041) is embedded in this ITO layer and electrically interconnected, ultimately forming a planar intermediate electrode unit (104) with both high conductivity and high light transmittance. Figure 8 The top and side views clearly show the interaction between the grid lines and the ITO thin film.
[0052] Step 4: Integration and device completion of the perovskite top solar cell (corresponding to...) Figure 9 ) On the prepared intermediate electrode unit (104) (i.e., ITO thin film 1042), a SnO2 thin film is prepared as an electron transport layer (1033) by reactive sputtering.
[0053] On the electron transport layer (1033), FaBr / FaI reacts with PbBr2 / PbI2 using a gas-solid reaction or solution method to form a FaPbIxBr3-x perovskite absorber layer (1032).
[0054] A NiOx thin film was prepared on the perovskite layer (1032) as a hole transport layer (1031) by reactive sputtering. At this point, the perovskite top cell (103) was completed.
[0055] The front gate electrode (101) is fabricated on the hole transport layer (1031) by means of a mask and physical vapor deposition.
[0056] Finally, a NbO2 / SiNx composite antireflection layer (102) was deposited on the outermost surface of the device using reactive sputtering, and electrode lead holes were etched by photolithography. The final overall structure of the device is as follows. Figure 9 As shown.
[0057] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A three-terminal, three-junction photovoltaic cell, characterized in that, The following layers are stacked sequentially along the direction of light incidence: Top-mounted battery cell, which is a perovskite cell; An intermediate electrode unit, which includes a transparent conductive layer; The intermediate battery unit is a gallium arsenide-based battery; Tunnel-through junction unit; The bottom battery cell is an indium gallium arsenide-based battery; The transparent conductive layer serves as an independent electrical port, electrically isolating the top battery unit from the stacked battery consisting of the lower intermediate battery unit, tunnel junction unit, and bottom battery unit, thereby giving the entire device three independent electrical output terminals.
2. The three-terminal, three-junction photovoltaic cell according to claim 1, characterized in that, The intermediate electrode unit further includes metal grid lines disposed on the transparent conductive layer, the metal grid lines being embedded in or disposed beneath the transparent conductive layer, the transparent conductive layer covering the entire surface of the intermediate battery unit.
3. The three-terminal triple-junction photovoltaic cell according to claim 1 or 2, characterized in that, The light absorption band gaps of the top battery unit, the middle battery unit, and the bottom battery unit decrease sequentially, and the photocurrent of each battery unit meets the requirements of series and parallel connection to avoid carrier accumulation. The separation and transmission directions of photogenerated carriers in the middle battery unit and the bottom battery unit are the same, and opposite to the separation and transmission directions of photogenerated carriers in the top battery unit and the middle battery unit.
4. The three-terminal triple-junction photovoltaic cell according to claim 1, characterized in that, The bottom battery cell has a distributed Bragg reflector layer on the side away from the tunnel junction.
5. The three-terminal, three-junction photovoltaic cell according to claim 1, characterized in that, The intermediate battery cell and the bottom battery cell are integrally formed on the original substrate by epitaxial growth and then transferred to the support substrate by a peeling process.
6. The three-terminal triple-junction photovoltaic cell according to claim 5, characterized in that, A sacrificial layer is provided between the original substrate and the intermediate battery cell.
7. A method for preparing a three-terminal, three-junction photovoltaic cell as described in any one of claims 1-6, characterized in that, The method comprises the following process modules executed sequentially: Epitaxial growth and substrate preparation of S1, III-V group dual-junction cells: On the original substrate, a buffer layer, a sacrificial layer, the intermediate cell unit, the tunnel junction unit and the bottom cell unit are epitaxially grown sequentially. S2, Substrate Transfer and Intermediate Cell Exposure: A back electrode is formed on the side of the bottom cell away from the tunnel junction and a supporting substrate is bonded. The sacrificial layer is then removed to remove the original substrate and expose the surface of the intermediate cell. S3. Integrated construction of intermediate electrode unit: On the exposed surface of the intermediate battery unit, a planarized intermediate electrode unit with both conductive and light-transmitting functions is prepared. S4. Integration of perovskite top cell: The top cell unit, antireflection layer and front grid electrode are sequentially fabricated on the intermediate electrode unit.
8. The method according to claim 7, characterized in that, The preparation of the intermediate electrode unit in step S3 specifically includes: First, a metal grid pattern is prepared on the surface of the intermediate battery cell; Subsequently, the transparent conductive layer is deposited while covering the metal grid lines and the entire battery surface to form the electrically interconnected and optically flat intermediate electrode unit.
9. The method according to claim 7, characterized in that, In step S1, the material of the sacrificial layer has a selective etching ratio with the materials of the buffer layer and the intermediate battery cell; in step S2, the sacrificial layer is removed by wet chemical etching.
10. The method according to claim 7, characterized in that, In step S4, when the top battery cell is fabricated on the intermediate electrode cell, the bottom functional transport layer of the top battery cell directly forms an ohmic contact with the intermediate electrode cell.