GaAs / pedot:pss@cnt heterojunction solar cell with electron transport layer and preparation method thereof

Abstract

This invention discloses a GaAs / PEDOT:PSS@CNT heterojunction solar cell with an electron transport layer and its fabrication method. The cell structure, from bottom to top, consists of a back electrode, an electron transport layer, a GaAs substrate, a PEDOT@CNT layer, and a top electrode. The fabrication method involves depositing a ZnO electron transport layer on the back side of the GaAs substrate using electron beam evaporation, followed by depositing an Au layer on the deposited ZnO as the back electrode. A PEDOT:PSS@CNT thin film is then fabricated on the surface of the GaAs substrate, followed by depositing one or more composite electrodes selected from Ag, Cr, Ti, Ni, and Au on the PEDOT:PSS@CNT thin film. This invention's solar cell fabrication method is not only simple and low-cost, but also utilizes the band structure characteristics of ZnO as the electron transport layer and PEDOT@CNT as a composite hole transport layer to improve device performance, which is beneficial for promoting the market development of GaAs-based solar cells.

Description

Technical Field

[0001] This invention relates to the technical field of solar cells, and more specifically, to a method for fabricating a GaAs / PEDOT:PSS@CNT heterojunction solar cell. Background Technology

[0002] In recent years, with the advent of the carbon neutrality concept, the development of green and clean energy has become a hot topic of social concern. Solar energy, as the most abundant clean energy source in nature, has naturally become a key research focus. Solar cells, as devices utilizing solar energy, are of great significance to the development and utilization of solar energy. GaAs is a direct bandgap semiconductor with a bandgap of 1.42 eV. Compared with traditional Si, it has higher theoretical efficiency, higher carrier mobility, and stronger radiation resistance. These advantages have led to the widespread application of GaAs solar cells in aerospace and other fields. However, most commonly used GaAs solar cells today are pn homojunction structures. Their fabrication requires equipment such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), as well as related epitaxial processes. These equipment are generally very expensive, and the process costs are also high, resulting in the high cost of GaAs solar cells. In contrast, heterojunction solar cells can effectively solve this problem. Currently, the development of high-efficiency organic hybrid heterojunction solar cells based on PEDOT:PSS or CNT hole transport thin films has simplified device fabrication processes and significantly reduced fabrication costs, and has been widely studied and reported. Besides the widely used pn homojunction, heterojunction solar cells also exist. Their structure consists of semiconductors and other transparent conductive materials to achieve directional carrier transport. Compared to pn homojunctions, the fabrication process of this type of heterojunction cell eliminates the demanding high-temperature epitaxial step, greatly reducing costs. Therefore, developing low-cost, high-performance GaAs heterojunction solar cells has become a research hotspot for many scholars. Furthermore, with the discovery of conductive polymers in the last century, their low cost and simple processing advantages have attracted widespread attention and rapid development. PEDOT:PSS, as a commonly used conductive polymer, is very inexpensive and is now widely used in solar cell research and development, with some success. Moreover, previous researchers have conducted theoretical calculations and simulations on the theoretical performance limits of GaAs / PEDOT:PSS solar cells, demonstrating great potential. However, in the current GaAs / PEDOT:PSS heterojunction hybrid solar cells, there is still considerable room for improvement in their performance. The reason for this, from the perspective of device structure, is that the lack of many functional layers leads to the loss of non-radiative recombination and charge carriers in the device, resulting in the incomplete realization of device performance. Summary of the Invention

[0003] To overcome the problems and shortcomings of the existing technology, this invention mainly proposes a method for fabricating GaAs / PEDOT:PSS@CNT heterojunction solar cells with a novel electron transport layer. A ZnO layer is deposited on the back side of the GaAs substrate as the electron transport layer, and PEDOT:PSS is combined with CNTs, which can effectively promote carrier migration rate, improve carrier separation, and enhance device performance. Therefore, this GaAs / PEDOT:PSS@CNT heterojunction solar cell structure is of great significance to the development of GaAs heterojunction solar cells.

[0004] The objective of this invention is achieved through the following technical steps:

[0005] A GaAs / PEDOT:PSS@CNT heterojunction solar cell with a novel electron transport layer comprises, from bottom to top, an Au back electrode, a ZnO electron transport layer, a GaAs substrate, a PEDOT:PSS@CNT layer, and a top electrode. In the PEDOT:PSS@CNT layer, PEDOT:PSS refers to an organic polymer, specifically poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and CNT refers to carbon nanotubes. This composite layer is prepared by spin-coating a PEDOT:PSS solution and a CNT dispersion after ultrasonic mixing.

[0006] In this invention, the open-circuit voltage of the solar cell is 0.50–0.55V, and the current density is 8.1–10.8 mA / cm². 2 The fill factor is 62.1–66.7%, and the photoelectric conversion efficiency is 2.77–3.53%.

[0007] A method for fabricating a GaAs / PEDOT:PSS@CNT heterojunction solar cell with a novel electron transport layer includes the following steps:

[0008] (1) A ZnO layer was deposited on the back side of a GaAs substrate as an electron transport layer by electron beam evaporation.

[0009] (2) A layer of Au is deposited on the surface of the ZnO thin film as a back electrode;

[0010] (3) A PEDOT:PSS@CNT thin film was prepared on the surface of a GaAs substrate;

[0011] (4) A composite electrode consisting of one or more of Ag, Cr, Ti, Ni and Au is deposited on the surface of PEDOT:PSS@CNT.

[0012] Preferably, the GaAs substrate is n-type doped.

[0013] Preferably, in step (3), the PEDOT:PSS@CNT film is prepared by spin coating, with a rotation speed of 3000-6000 rpm and a spin coating time of 10s-20s.

[0014] Preferably, in step (1), after the ZnO thin film is deposited by vapor deposition, it needs to be annealed under vacuum conditions at a temperature of 350℃-400℃.

[0015] Preferably, in step (3), after the PEDOT:PSS@CNT film is prepared, it needs to be annealed under vacuum conditions at a temperature of 120℃-150℃.

[0016] Specifically, the following steps are included:

[0017] (1) The GaAs substrate is cleaved into specific sizes according to requirements to facilitate subsequent substrate cleaning and solar cell device fabrication.

[0018] (2) The GaAs substrates were ultrasonically cleaned for 5 minutes with isopropanol, ethanol and deionized water respectively to remove organic matter on the surface. Then, the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% dilute hydrochloric acid.

[0019] (3) A ZnO layer was deposited on the back side of the GaAs substrate as an electron transport layer by electron beam evaporation.

[0020] (4) A layer of metal is deposited on the surface of the ZnO thin film as a back electrode;

[0021] (5) The substrate with the vapor-deposited back electrode is sent into an annealing furnace for rapid annealing.

[0022] (6) Prepare PEDOT:PSS@CNT thin films on the surface of GaAs substrates;

[0023] (7) A layer of metal is deposited on the surface of PEDOT:PSS@CNT as the top electrode.

[0024] In step (1) of the above method, the specific size of the GaAs substrate can be 0.5cm×0.5cm, 0.7cm×0.7cm, 1.0cm×1.0cm, 1.5cm×1.5cm, 2.0cm×2.0cm, etc., not exceeding 4cm. 2 The square size.

[0025] In step (1) of the above method, the GaAs substrate is n-type doped with a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0026] In step (3) of the above method, the thickness of the vapor-deposited ZnO film is 20-50 nm.

[0027] In step (3) of the above method, after the ZnO thin film is deposited by vapor deposition, it needs to be annealed under vacuum conditions at a temperature of 350℃-400℃.

[0028] In step (4) of the above method, the back electrode metal used can be one or more of the following metals: Au, Pt, Ni, Ti, etc.

[0029] In step (4) of the above method, the thickness of the back electrode deposited by vapor deposition is 100-150 nm.

[0030] In step (4) of the above method, the annealing atmosphere of the back electrode is nitrogen atmosphere, the annealing temperature is 300-350℃, and the annealing time is 30-60s.

[0031] In step (6) of the above method, PEDOT:PSS in the PEDOT:PSS@CNT film refers to an organic polymer, whose full Chinese name is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and the specific model is Clevios. TM P1000, CNT refers to carbon nanotubes. This composite layer is made by spin-coating a PEDOT:PSS solution and a CNT dispersion after ultrasonic mixing.

[0032] In step (6) of the above method, the concentration of the PEDOT:PSS@CNT solution is 10mg / mL-30mg / mL.

[0033] In step (6) of the above method, the PEDOT:PSS@CNT film is prepared by spin coating, with a rotation speed of 3000-6000 rpm and a spin coating time of 10s-20s.

[0034] In step (6) of the above method, after the PEDOT:PSS@CNT film is prepared, it needs to be annealed under vacuum conditions at a temperature of 120℃-150℃.

[0035] In step (7) of the above method, the top electrode prepared is one or more composite metal electrodes selected from Ag, Cr, Ti, Ni, and Au.

[0036] In step (7) of the above method, the thickness of the top electrode is 100-120 nm.

[0037] The principle of this invention is as follows:

[0038] ZnO, as a semiconductor, is used in the GaAs / PEDOT:PSS@CNT solar cell structure. The band structure relationships among the three components are as follows:Figure 3 As shown, the insertion of a ZnO layer introduces a new band structure between the GaAs substrate and the Au back electrode. The figure shows that, compared to a simple GaAs / Au contact, the presence of the ZnO electron transport layer reduces the electron transition barrier from 1.03 eV to 0.8 eV. Furthermore, the conduction band bottom position between the GaAs substrate and the ZnO electron transport layer differs by only 0.23 eV, effectively lowering the electron transport barrier and increasing the electron transition probability. The addition of CNTs also improves the hole mobility of the PEDOT:PSS@CNT layer, promoting carrier separation and thus enhancing device performance.

[0039] Compared with existing technologies, the present invention has the following advantages and beneficial effects:

[0040] Compared to conventional GaAs / PEDOT:PSS heterojunction solar cells, electron transport layers can be fabricated through simple evaporation and annealing processes, improving device performance while maintaining lower costs. Furthermore, the insertion of ZnO layers can promote electron migration, and the application of PEDOT:PSS@CNT layers reduces carrier recombination, thereby improving device performance without conflicting with other functional layers. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the structure of the GaAs / PEDOT:PSS@CNT heterojunction solar cell in an embodiment of the present invention;

[0042] Figure 2 This is a molecular structure diagram of the PEDOT:PSS conductive polymer used in this invention;

[0043] Figure 3 This is a band structure diagram showing the energy band relationship between the ZnO electron transport layer used in this invention, when it is between the GaAs and Au back electrodes.

[0044] Figure 4 The JV curve of the GaAs / PEDOT:PSS@CNT heterojunction solar cell in this embodiment of the invention;

[0045] Figure 1 The components are as follows:

[0046] Au back electrode 1, ZnO electron transport layer 2, GaAs substrate 3, PEDOT:PSS@CNT layer 4, top electrode 5. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0048] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0049] Example 1

[0050] This embodiment describes a method for fabricating a GaAs / PEDOT:PSS@CNT heterojunction solar cell with a novel electron transport layer, the structural schematic of which is shown below. Figure 1 As shown, it includes, from bottom to top, an Au back electrode 1, a ZnO electron transport layer 2, a GaAs substrate 3, a PEDOT:PSS@CNT layer 4, and a top electrode 5.

[0051] The GaAs / PEDOT:PSS@CNT heterojunction solar cell described above is fabricated using the following method:

[0052] (1) Cleave the GaAs substrate into squares of 1.0cm × 1.0cm as required;

[0053] (2) The GaAs substrates were ultrasonically cleaned for 5 minutes with isopropanol, ethanol and deionized water respectively to remove organic matter on the surface. Then, the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% dilute hydrochloric acid.

[0054] (3) A 30 nm thick ZnO layer was deposited on the back side of an n-type doped GaAs substrate by electron beam evaporation.

[0055] (4) Anneal the GaAs substrate with ZnO layer at 350°C in vacuum for 10 minutes;

[0056] (5) A 120nm thick layer of Au is deposited on the ZnO layer as the back electrode;

[0057] (6) The substrate with the evaporated Au back electrode is sent into an annealing furnace for rapid annealing in a nitrogen atmosphere. The annealing temperature is 320℃ and the annealing time is 30s.

[0058] (7) A PEDOT@CNT mixed solution was spin-coated onto the upper surface of a GaAs substrate. The PEDOT:PSS concentration of the mixed solution precursor was 15 mg / mL, and the concentration of the CNT dispersion was 1×

[0059] 10 -3 mg / ml, the volume fraction of the mixed solution PEDOT:PSS is 80%, spin-coated at 3000 rpm for 15 seconds;

[0060] (8) The spin-coated PEDOT:PSS@CNT film was annealed under vacuum conditions at a temperature of 130°C for 5 minutes.

[0061] (9) A 110nm Au layer was deposited on the annealed PEDOT:PSS as the top electrode.

[0062] Figure 4 This is the JV curve of the GaAs / PEDOT:PSS@CNT heterojunction solar cell prepared in Example 1.

[0063] The open-circuit voltage of the solar cell is 0.55V, and the current density is 9.6mA / cm². 2 The fill factor is 66.7%, and the photoelectric conversion efficiency is 3.52%.

[0064] Example 2

[0065] (1) Cleave the GaAs substrate into squares of 1.0cm × 1.0cm as required;

[0066] (2) The GaAs substrates were ultrasonically cleaned for 5 minutes with isopropanol, ethanol and deionized water respectively to remove organic matter on the surface. Then, the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% dilute hydrochloric acid.

[0067] (3) A 30 nm ZnO layer was deposited on the back side of an n-type doped GaAs substrate by electron beam evaporation.

[0068] (4) Anneal the GaAs substrate with ZnO layer at 400°C in vacuum for 10 minutes;

[0069] (5) A 120nm Au layer is deposited on the ZnO layer as a back electrode;

[0070] (6) The substrate with the evaporated Au back electrode is sent into an annealing furnace for rapid annealing in a nitrogen atmosphere. The annealing temperature is 320℃ and the annealing time is 30s.

[0071] (7) A layer of PEDOT:PSS@CNT solution was spin-coated onto the upper surface of the GaAs substrate. The concentration of PEDOT:PSS in the mixed solution precursor was 15 mg / mL, and the concentration of CNT solution was 1 × 10⁻⁶. -3 mg / ml, the volume fraction of the mixed solution PEDOT:PSS is 70%, spin-coated at 3000 rpm for 15 seconds;

[0072] (8) The spin-coated PEDOT:PSS@CNT film was annealed under vacuum conditions at a temperature of 130°C for 5 minutes.

[0073] (9) A 110nm Au layer was deposited on the annealed PEDOT:PSS@CNT as the top electrode.

[0074] Example 3

[0075] (1) Cleave the GaAs substrate into squares of 1.0cm × 1.0cm as required;

[0076] (2) The GaAs substrates were ultrasonically cleaned for 5 minutes with isopropanol, ethanol and deionized water respectively to remove organic matter on the surface. Then, the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% dilute hydrochloric acid.

[0077] (3) A 30 nm ZnO layer was deposited on the back side of an n-type doped GaAs substrate by electron beam evaporation.

[0078] (4) Anneal the GaAs substrate with ZnO layer at 400°C in vacuum for 10 minutes;

[0079] (5) A 120nm Au layer is deposited on the ZnO layer as the back electrode;

[0080] (6) The substrate with the evaporated Au back electrode is sent into an annealing furnace for rapid annealing in a nitrogen atmosphere. The annealing temperature is 330℃ and the annealing time is 30s.

[0081] (7) A PDOTE:PSS@CNT composite solution was spin-coated onto the upper surface of a GaAs substrate. The concentration of the PDOTE:PSS precursor in the mixed solution was 15 mg / mL, and the concentration of the CNT solution was 1 × 10⁻⁶. -3 mg / ml, the volume fraction of the mixed solution PEDOT:PSS is 70%, spin-coated at 3000 rpm for 15 seconds;

[0082] (8) The spin-coated PEDOT:PSS@CNT film was annealed under vacuum conditions at a temperature of 150°C for 5 minutes.

[0083] (9) An Ag layer is deposited on the annealed PEDOT:PSS as the top electrode.

[0084] Comparative Example 1

[0085] This comparative example illustrates a method for fabricating a GaAs / PEDOT:PSS heterojunction solar cell, and its structural schematic diagram is shown below. Figure 1 As shown, it includes a back electrode, a GaAs substrate, a PEDOT:PSS layer, and a top electrode stacked sequentially from bottom to top.

[0086] The GaAs / PEDOT:PSS heterojunction solar cell described above is fabricated using the following method:

[0087] (1) Cleave the GaAs substrate into squares of 1.0cm × 1.0cm as required;

[0088] (2) The divided GaAs substrates were ultrasonically cleaned with isopropanol, ethanol and deionized water respectively for 5 minutes.

[0089] After 10 minutes, the organic matter on the surface was washed away, and then the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% by mass dilute hydrochloric acid.

[0090] (3) A 120 nm Au layer was deposited on the back side of an n-type doped GaAs substrate using electron beam evaporation as a back electrode;

[0091] (4) The n-type GaAs substrate with Au back electrode was rapidly annealed at 350°C in a nitrogen atmosphere for 30s.

[0092] (5) Spin-coat a layer of PDOTE:PSS solution with a concentration of 15 mg / mL on the upper surface of the GaAs substrate for 15 seconds at a speed of 3000 rpm.

[0093] (6) The spin-coated PEDOT:PSS solution was annealed under vacuum at a temperature of 110°C for 5 minutes.

[0094] (7) A 120nm Ag layer was deposited on the annealed PEDOT:PSS as the top electrode.

[0095] The device performance of the GaAs / PEDOT:PSS heterojunction solar cell prepared in Example 1 is shown in Table 1. The open-circuit voltage of the solar cell is 0.47V, and the current density is 3.1mA / cm². 2 The fill factor is

[0096] 48.3%, with a photoelectric conversion efficiency of 0.70%.

[0097] Comparative Example 2

[0098] This comparative example illustrates a method for fabricating a GaAs / graphene heterojunction solar cell, the structural schematic of which is shown below. Figure 1 As shown, it includes a back electrode, a GaAs substrate, a graphene layer, and a top electrode stacked from bottom to top.

[0099] The GaAs / graphene heterojunction solar cell described above is fabricated using the following method:

[0100] (1) Cleave the GaAs substrate into squares of 0.5cm × 0.5cm as required;

[0101] (2) The GaAs substrates were ultrasonically cleaned for 5 minutes with isopropanol, ethanol and deionized water respectively to remove organic matter on the surface. Then, the intrinsic oxide layer on the surface of the GaAs substrate was removed with 10% dilute hydrochloric acid.

[0102] (3) A 120 nm Au layer was deposited on the back side of an n-type doped GaAs substrate using electron beam evaporation as a back electrode;

[0103] (4) The n-type GaAs substrate with Au back electrode was rapidly annealed at 350°C in a nitrogen atmosphere for 30s.

[0104] (5) Cut the purchased graphene film into 0.5cm×0.5cm squares as needed, and place it in an aqueous solution for wet transfer to transfer the graphene onto a GaAs substrate with an Au back electrode.

[0105] (6) Place the GaAs substrate with transferred graphene in a vacuum vessel, remove the water using a machine, then drop 50°C acetone solution onto the graphene surface to remove the PMMA involved, and wash away the acetone to obtain a pure GaAs / graphene heterojunction.

[0106] (7) A 120nm Ag layer was deposited on the annealed PEDOT:PSS as the top electrode.

[0107] The device performance of the GaAs / graphene heterojunction solar cell prepared in Example 2 is shown in Table 1. The open-circuit voltage of the solar cell is 0.51V, and the current density is 10.06mA / cm². 2 The fill factor is

[0108] 51.98%, with a photoelectric conversion efficiency of 2.65%.

[0109] The preparation conditions of Comparative Examples 1 and 2 were similar to those of Example 1, except that ZnO electron transport layers and CNTs were not used. In addition, since Comparative Example 2 used two-dimensional materials to prepare heterojunctions, the cost was higher than that of organic materials, and it was not suitable for large-scale production.

[0110] The performance parameters of Comparative Examples 1-2 and Examples 1-3 were compared using a solar simulator and are shown in Table 1.

[0111] Table 1. Performance parameters of GaAs heterojunction solar cells obtained in Examples 1-3 and Comparative Examples 1-2.

[0112]

[0113]

[0114] As shown in Table 1, the fill factor of Examples 1-3 was significantly improved compared with Comparative Examples 1-2. This is related to the characteristic that PEDOT:PSS@CNT can easily form good contacts, which can directly improve device performance. In addition, compared with Comparative Example 1 without an electron transport layer, the current density of Examples 1-3 was significantly improved. This proves the role of the ZnO electron transport layer, which can promote electron transport and carrier separation, thereby increasing the device current.

[0115] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A GaAs / PEDOT:PSS@CNT heterojunction solar cell with an electron transport layer, characterized in that, The solar cell, from bottom to top, consists of an Au back electrode, a ZnO electron transport layer, an n-type doped GaAs substrate, a PEDOT:PSS@CNT layer, and a top electrode. After the ZnO electron transport layer is deposited by vapor deposition, it is annealed under vacuum conditions at 350℃-400℃. In the PEDOT:PSS@CNT layer, PEDOT:PSS refers to poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and CNT refers to carbon nanotubes; the PEDOT:PSS@CNT layer is composed of a PEDOT:PSS solution with a concentration of 10 mg / mL-30 mg / mL and a 1×10⁻⁶ solution. -3 mg / mL~3×10 -3 The CNT dispersion of mg / mL was mixed with PEDOT:PSS solution at a volume fraction of 30% to 90%, and after ultrasonic treatment to form a uniform dispersion, it was spin-coated onto the surface of GaAs substrate and then annealed under vacuum at 120℃-150℃. The open-circuit voltage of the solar cell is 0.50V to 0.55V, and the short-circuit current density is 8.1mA / cm². 2 ~10.8mA / cm 2 The fill factor is 62.1%–66.7%, and the photoelectric conversion efficiency is 2.77%–3.53%. The method for fabricating the GaAs / PEDOT:PSS@CNT heterojunction solar cell with an electron transport layer includes the following steps: (1) A layer of ZnO is deposited on the back side of the GaAs substrate as an electron transport layer by electron beam evaporation. After the ZnO thin film is deposited, it needs to be annealed under vacuum conditions at a temperature of 350℃-400℃. (2) A layer of Au is deposited on the surface of the ZnO thin film as a back electrode; (3) A PEDOT:PSS@CNT thin film was prepared on the GaAs substrate. The PEDOT:PSS@CNT thin film was prepared by spin coating at a speed of 3000-6000 rpm for 10-20 seconds. After the PEDOT:PSS@CNT thin film was prepared, it was annealed under vacuum at a temperature of 120-150℃. PEDOT:PSS in the PEDOT:PSS@CNT thin film refers to an organic polymer, whose full Chinese name is poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and CNT refers to carbon nanotubes. The composite layer was prepared by spin coating after mixing PEDOT:PSS solution and CNT dispersion by ultrasonic means. The concentration of PEDOT:PSS solution was 10 mg / mL-30 mg / mL, and the concentration of CNT dispersion was 1×10⁻⁶. -3 mg / ml~3×10 -3 mg / ml; The volume fraction of PEDOT:PSS solution in the PEDOT:PSS@CNT mixture is 30%–90%; (4) A composite electrode consisting of one or more of Ag, Cr, Ti, Ni and Au is deposited on the surface of PEDOT:PSS@CNT; the GaAs substrate is n-type doped.

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