CN106159003B - A kind of photovoltaic devices and a kind of method for producing photovoltaic effect - Google Patents

Abstract

The invention provides a photovoltaic device, including a light source and a photovoltaic device, the photovoltaic device includes a high-blocking light-gain semiconductor substrate, a graphene layer on the high-blocking light-gain semiconductor substrate, and a graphene layer on the high-blocking light-gain semiconductor substrate. A first electrode and a second electrode on the gain semiconductor substrate and the graphene layer, wherein a part of the first electrode is in contact with the high-resistance optical gain semiconductor substrate, and another part is in contact with the graphene layer , a part of the second electrode is in contact with the high-resistance optical gain semiconductor substrate, and another part is in contact with the graphene layer, wherein the energy of the light emitted by the light source is greater than that of the high-resistance optical gain semiconductor substrate the band gap. The photovoltaic device fully utilizes the advantages of each component, and has high photoelectric conversion efficiency.

Description

Photovoltaic device and method for producing photovoltaic effect

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a photovoltaic device and a method for generating photovoltaic effects.

Background technique

Since the invention of semiconductor transistors by scientists John Bardeen and Walter Brattain of Bell Laboratories in 1947, PN junctions have been widely used in modern semiconductor optoelectronic components and systems as the basic structural unit of modern semiconductor devices. Based on the photovoltaic effect of the PN junction principle, Bell Laboratories made a practical monocrystalline silicon photovoltaic cell with a photoelectric conversion efficiency of 6% for the first time in 1954, creating a new era of photovoltaic power generation. For more than half a century, all photovoltaic devices developed and utilized have followed this principle. However, the complex device process and large device size of the traditional semiconductor PN junction limit its wide application, especially in the application of micro-nano devices and flexible devices.

With the emergence of graphene as a new two-dimensional material, the excellent optoelectronic properties of graphene and the thickness of only a single atomic layer provide opportunities for graphene-based devices. "Graphene photodetectors for high-speed optical communications" published by Thomas Mueller et al. on nature Photonics in 2010 and "Tunable photoresponse of epitaxial graphene on SiC" published by Rujie Sun et al. on Applied Physics Letters in 2013 respectively disclosed a method based on Graphene photovoltaic devices, but in these two documents, the photovoltaic effect is based on the photothermoelectric effect, requiring the substrate of the photovoltaic device to have no absorption of irradiated light as much as possible, which greatly limits the selection of light sources. Meanwhile, the absorption of irradiated light in the above documents is achieved by metal or graphene. Due to the characteristics of the photothermoelectric effect and the thickness of the single atomic layer of graphene, the absorption rate of irradiated light by graphene-based photovoltaic devices in the prior art is only 2.3%, and the photoelectric conversion efficiency is low.

Contents of the invention

Therefore, the object of the present invention is to overcome the deficiencies in the above-mentioned prior art, and a kind of highly sensitive photovoltaic device that fully utilizes the advantage of each component (comprising substrate, metal electrode and graphene) is provided, comprises light source and photovoltaic device, so The photovoltaic device includes a high-blocking optical gain semiconductor substrate, a graphene layer located on the high-blocking optical gain semiconductor substrate, a first electrode and a first electrode located on the high-blocking optical gain semiconductor substrate and the graphene layer A second electrode, wherein a part of the first electrode is in contact with the high-resistance optical gain semiconductor substrate, another part is in contact with the graphene layer, and a part of the second electrode is in contact with the high-resistance optical gain semiconductor substrate. The other part is in contact with the graphene layer, wherein the energy of the light emitted by the light source is greater than the band gap of the high-resistance optical gain semiconductor substrate.

According to the photovoltaic device of the present invention, preferably, the high-resistance optical gain semiconductor substrate is a high-resistance organic semiconductor or a high-resistance inorganic semiconductor.

According to the photovoltaic device of the present invention, preferably, the high-blocking light-gain semiconductor substrate is a single body or a semi-insulating film grown on the substrate.

According to the photovoltaic device of the present invention, preferably, the light source is an ultraviolet light source, the high-blocking light gain semiconductor substrate is SiC, or the light source is a visible light source, and the high-blocking light gain semiconductor substrate is GaP or GaAs .

According to the photovoltaic device of the present invention, preferably, the thickness of the high-blocking light-gain semiconductor substrate is greater than 50 nm.

According to the photovoltaic device of the present invention, preferably, the length of the graphene layer between the first electrode and the second electrode is greater than 3 μm.

According to the photovoltaic device of the present invention, preferably, the first electrode and the second electrode are metal electrodes.

According to the photovoltaic device of the present invention, preferably, the difference between the electron work function of the metal electrode and the electron work function of the high-blocking optical gain semiconductor substrate is greater than 0.1 eV.

According to the photovoltaic device of the present invention, preferably, the first electrode and the second electrode use the same metal.

According to the photovoltaic device of the present invention, preferably, it further includes an opaque coating layer on the first electrode or the second electrode.

According to the photovoltaic device of the present invention, preferably, it further includes a first lead and a second lead electrically connected to the first electrode and the second electrode, respectively.

According to the photovoltaic device of the present invention, preferably, it also includes a package for encapsulating the high resistance optical gain semiconductor substrate, the graphene layer, the first and second electrodes, and the first and second leads A housing, wherein the encapsulating housing has a light-through window.

The present invention also provides a method for producing a photovoltaic effect, comprising irradiating a photovoltaic device with a light source, the photovoltaic device comprising a high-blocking light-gain semiconductor substrate, a graphene layer positioned on the high-blocking light-gain semiconductor substrate, A first electrode and a second electrode located on the high resistance light gain semiconductor substrate and the graphene layer, wherein a part of the first electrode is in contact with the high resistance light gain semiconductor substrate, and another part is in contact with the high resistance light gain semiconductor substrate The graphene layer is in contact, a part of the second electrode is in contact with the high-resistance optical gain semiconductor substrate, and the other part is in contact with the graphene layer, and the method includes: using the light whose energy is greater than the high A light source blocking the bandgap of the gain semiconductor substrate illuminates the photovoltaic device.

Compared with the prior art, the photovoltaic device of the present invention makes full use of the support substrate of the graphene device compared to the effective absorption of irradiated light with high band gap energy, and a large number of carriers generated are quickly transferred to the metal of the graphene device. On the electrodes, the photovoltaic effect occurs if the photovoltaic device is properly configured such that a voltage difference is established across the graphene electrodes. Since the supporting substrate of the graphene device is a bulk material or a thin film material, its absorption of irradiated light is strong. Compared with the prior art solution, the photovoltaic device of the present invention has more obvious photovoltaic effect and higher photoelectric conversion efficiency. The photovoltaic device of the invention can be widely used in organic and inorganic semiconductor material systems to prepare flexible, micro-nano-scale photovoltaic components. Especially under short-circuit conditions, the photovoltaic device also serves as an ultrafast, sensitive photodetector that does not require an external power source.

Description of drawings

Embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

1 is a schematic diagram of a cross-sectional structure of a photovoltaic device according to the present invention;

Fig. 2 is a top view of the photovoltaic device 100 in the photovoltaic device shown in Fig. 1, without showing the leads;

Figure 3 is a schematic diagram of the energy band structure of the metal electrode Ti and SiC heterojunction interface, where E _C , _EV and _EF represent the conduction band, valence band and Fermi level of SiC, respectively;

Figure 4 is a schematic diagram of the energy band structure of graphene and metal electrode Ti under the condition of light, where ΔE is the case where the left electrode is irradiated by light with photon energy hν (its energy is greater than the band gap of high resistance optical gain semiconductor) , the Fermi level difference generated at both ends of the graphene;

Figure 5 is a schematic diagram of the energy band structure of graphene and metal electrode Ti in the absence of light;

Figure 6 is a schematic diagram of the energy band structure of the interface between graphene and SiC heterojunction;

Fig. 7 is the photocurrent response curve of the photovoltaic device of the specific example of the present invention under short-circuit condition;

8 is a schematic top view of a photovoltaic device structure in another example of the present invention;

Fig. 9 is a schematic cross-sectional structure diagram of a photovoltaic device structure in another example of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In order to fully utilize and tap the role of all participating components in a graphene-based photovoltaic device, the present invention proposes a photovoltaic device whose substrate is absorbable to irradiated light. Since the thickness of the substrate material is much larger than that of the metal electrode or graphene, the photogenerated carriers generated by its efficient absorption of irradiated light can be under the action of the electric field at the substrate/metal interface and the electric field at the substrate/graphene interface. Fast transfer to the metal electrode or graphene, causing a change in the Fermi level of the metal electrode or graphene. By using asymmetric metal electrodes or asymmetric irradiated light, the photovoltaic device of the present invention quickly establishes a voltage between the metal electrodes at both ends of the graphene under the irradiation of irradiated light that can be absorbed by the substrate, thereby generating a photovoltaic voltage . Moreover, the inventors also found that the photovoltaic voltage generated by the photovoltaic device of the present invention is actually the result of the superposition of the photovoltaic effect generated by substrate absorption and the photothermoelectric effect of metal electrodes and graphene, and the latter is almost negligible compared to the former , so the photoelectric conversion efficiency of the photovoltaic device of the present invention is much higher than that of the prior art photovoltaic devices.

first embodiment

1 shows a schematic diagram of a cross-sectional structure of a photovoltaic device according to the present invention, including a photovoltaic device 100 and a light source 200 for irradiating the photovoltaic device 100. The photovoltaic device 100 includes a high-blocking light-gain semiconductor substrate 1 located on a high-blocking light-gaining semiconductor substrate 1. The graphene layer 2 on the gain semiconductor substrate 1, the first electrode 31 and the second electrode 32 on the high-resistance light gain semiconductor substrate 1 and the graphene layer 2, and the first and second electrodes 31, 32 respectively Electrically connected first and second leads 41, 42, wherein a part of the first electrode 31 is in contact with the high-resistance optical gain semiconductor substrate 1, another part is in contact with the graphene layer 2, and a part of the second electrode 32 is in contact with the high-resistance optical gain semiconductor substrate 1. The optical gain semiconductor substrate 1 is in contact, and the other part is in contact with the graphene layer 2 . FIG. 2 is a top view of the photovoltaic device 100 in the photovoltaic device shown in FIG. 1 , where the first and second leads 41 and 42 are not shown. ,

In the photovoltaic device of the present invention, the high-resistance light-gain semiconductor substrate 1 of the photovoltaic device is used as the support substrate of the graphene layer 2 and the first and second electrodes 31, 32, and more importantly, the high-resistance light-gain semiconductor substrate Bottom 1 is used as a photosensitive material. When the light emitted by the light source with energy greater than the band gap of the high-blocking light-gain semiconductor substrate is irradiated on the prepared photovoltaic device, the large light-absorbing volume of the high-blocking light-gain semiconductor substrate enhances the contrast to other materials. The absorption of photon energy with high band gap energy generates a large number of photogenerated carriers in the semiconductor substrate with high resistance to light gain.

The electrodes 31 and 32 of the photovoltaic device in the photovoltaic device of the present invention are not only the electrodes at both ends of the photovoltaic device of the present invention, but also receive the photogenerated carriers transferred from the high resistance optical gain semiconductor substrate 1 to the electrode 31 or electrode 32 . According to an embodiment of the present invention, preferably, the electrodes 31 and 32 are metal electrodes. More preferably, the electron work function of the metal electrode is quite different from the electron work function of the high-resistance optical gain semiconductor substrate (the difference should be greater than 0.1 eV). Due to the balance requirement of the Fermi level at the interface between the high-resistance light-gain semiconductor material and the metal electrode, an electric field is formed at the interface that is conducive to the drift of photo-generated carriers from the high-resistance light-gain semiconductor substrate to the metal electrode. The built-in electric field helps the photogenerated carriers to transfer rapidly from the high-resistance light-gain semiconductor substrate to the metal electrode. Those skilled in the art can easily understand that when the light causes the high-resistance optical gain semiconductor substrate to transfer carriers at different rates on the electrodes 31 and 32 at the two ends of the graphene layer 2, it will result in a gap in the graphene layer 2. The Fermi energy gap is generated on the electrodes at both ends, thereby generating the photovoltaic effect. However, in order to form different Fermi levels on the electrodes 31 and 32 at the two ends of the graphene layer 2 under light conditions, it can be realized by the following two situations: the first, the electrodes 31 and 32 are symmetrical, that is, the electrodes 31 and 32 are symmetrical. The material type of 32 and its area on the semiconductor substrate with high resistance light gain are all the same. In this case, the light emitted by the light source only irradiates one of the two electrodes 31 or 32, which will make the Fermi of the irradiated electrode The energy level changes, so that the two electrodes produce a very poor Fermi energy. Those skilled in the art can easily understand that one of the two electrodes can also be coated with an opaque layer. At this time, the light emitted by the light source is evenly distributed. Irradiating the entire device creates a Fermi energy gap between the two electrodes. Of course, it can also be understood that if the light source is a light source group containing two light sources emitting different lights, or the light emitted by the light source is divided into two different beams by another beam splitting device, the two different beams of light are respectively irradiated to the two electrodes 31 and 32, the two electrodes will also produce a Fermi level difference; second, the electrodes 31 and 32 are asymmetrical, that is, the materials of the electrodes 31 and 32 are different or the areas on the high-resistance optical gain semiconductor substrate are different or the two electrodes are asymmetrical. In this case, there is no limitation on whether the light emitted by the light source illuminates the entire device or a single electrode. In the simplest case, a beam of uniform light emitted by the light source irradiates the entire device. Obviously, the device fabrication process in the former case is simpler and easier to operate.

The graphene layer 2 of the photovoltaic device in the photovoltaic device of the present invention acts as a connection medium between two electrodes, and its size (including length and width) between the two electrodes 31 and 32 directly affects the magnitude of the photovoltaic voltage. In principle, the longer and narrower the graphene layer between the two electrodes 31, 32, the more prominent its photovoltaic effect. At the same time, the graphene layer 2 also receives the photogenerated carriers transferred from the high-resistance light-gain semiconductor substrate 1 to change the Fermi level, thereby affecting the response rule of the short-circuit photocurrent. Based on short-circuit photocurrent detection, the photovoltaic device can act as an ultrafast photodetector.

The photovoltaic device of the present invention will be described below through specific examples.

Referring to Fig. 1, illustrate the specific example of the photovoltaic device of the present invention, it comprises photovoltaic device 100 and ultraviolet light source 200, photovoltaic device 100 comprises SiC substrate 1, is positioned at the graphene layer 2 on SiC substrate 1, is positioned at SiC substrate 1 and The Ti metal electrode 31 and the Ti metal electrode 32 on the graphene layer 2, a part of the Ti metal electrode 31 is in contact with the SiC substrate 1, another part is in contact with the graphene layer 2, and a part of the Ti metal electrode 32 is in contact with the SiC substrate 1 , and the other part is in contact with the graphene layer 2. Wherein, the thickness of the SiC substrate 1 is 350 μm; the length×width of the graphene layer between the two electrodes is 100 μm×10 μm.

Experiments have found that if ultraviolet light with energy greater than the band gap of SiC is irradiated on one of the electrodes of the prepared photovoltaic device, electrons in the valence band of SiC in the irradiation area can be excited to transition to the conduction band. However, the photogenerated carriers generated in SiC are quickly transferred to the metal electrode irradiated by ultraviolet light under the action of the interface electric field between SiC and metal electrode (metal Ti) (as shown in Figure 3), resulting in the contact between graphene and metal. There is a potential energy difference between the Fermi levels at the electrodes at both ends (as shown in Figure 4), so a voltage difference of tens or even hundreds of millivolts can be generated at both ends of the electrodes. For comparison, Fig. 5 shows a schematic diagram of the energy band structures of graphene and metal electrodes in the absence of light.

In addition, at the heterojunction interface formed by graphene and SiC, the photogenerated carriers generated in SiC can also be transferred from the conduction band of SiC to graphene. However, since the electronic work function of graphene is close to that of SiC, the energy band bending at the heterojunction interface between graphene and SiC is small (as shown in Figure 6), and the electron energy in graphene is similar to that of SiC. Electrons with close valence band electron energies will flow back to the valence band of SiC, resulting in the same or little change in the number of net carriers in graphene. Fig. 7 is under the short-circuit condition, under the situation that the ultraviolet light of 325nm of different powers only irradiates the large-area electrode 31, the photocurrent response curve (the curve from bottom to top corresponds to 0mW (no light), 2mW, 3mW, 5mW respectively and the photocurrent response law under 10mW ultraviolet light irradiation), the magnitude of the applied voltage value corresponding to the intersection of each curve and the horizontal axis is equal to the magnitude of the photovoltaic voltage generated by the photovoltaic device.

Fig. 8 is a schematic structural diagram of a photovoltaic device in a photovoltaic device according to another example of the present invention. In this example, the unshown light source is 532nm green light with energy greater than 2.3eV; the high-resistance optical gain semiconductor substrate adopts GaP single wafer; the first electrode 31 is Ti metal, and the second electrode 32 is Pt metal. Wherein, the thickness of the GaP single wafer is 300 μm; the area of the first electrode 31 is equal to the area of the second electrode 32 ; the length×width of the graphene layer between the two electrodes is 10 μm×3 μm.

Fig. 9 is a schematic structural diagram of a photovoltaic device in a photovoltaic device according to another example of the present invention. In this example, the unshown light source is 632nm red light with energy greater than 1.42eV; the high-resistance optical gain semiconductor substrate adopts a semi-insulating GaAs film epitaxially grown on a Si substrate; the first electrode 31 and the second electrode 32 are all Ti metals. Wherein, the thickness of the GaAs thin film is 100 nm; the length×width of the graphene layer between the two electrodes is 5 μm×3 μm.

According to other examples of the present invention, the material of the high-blocking optical gain semiconductor substrate is an organic or inorganic semiconductor material, and the thickness of the substrate is greater than 50nm;

According to other examples of the present invention, the first electrode and the second electrode are made of the same metal, and preferably, an opaque layer is coated on one of the electrodes on the high-resistance optical gain semiconductor substrate. Those skilled in the art can understand that in the present invention, the shape of the electrodes is not limited in any way;

According to other examples of the present invention, the first electrode and the second electrode are different metals. Preferably, if the electronic work functions of the two electrodes are both smaller than the electronic work function of the high-resistance optical gain semiconductor 1, the light emitted by the light source should be irradiated to the maximum extent on the metal electrode with a relatively small electronic work function on the high-resistance optical gain semiconductor substrate. on the bottom. If the work function of one electrode is smaller than the work function of the high-resistance optical gain semiconductor 1, and the electronic work function of the other electrode is greater than the electronic work function of the high-resistance optical gain semiconductor 1, the irradiation of the light emitted by the light source on the two metal electrodes The method is not strictly limited. The irradiation mode and direction of the light beam emitted by the light source can be implemented in a manner known in the art.

According to other examples of the present invention, the length of the graphene layer between the two metal electrodes is greater than 3 μm.

According to other examples of the present invention, the photovoltaic device of the present invention may further include an encapsulation case encapsulating the high-resistance light-gain semiconductor substrate, the graphene layer, electrodes and leads, and the encapsulation case has a light-through window.

In order to embody the effect of the present invention, the contriver has carried out comparative experiment, adopts the ultraviolet light source (light spot diameter is about 150 μ m) of the 325nm ultraviolet light source (light spot diameter) of 10mW to irradiate an electrode of the photovoltaic device in the photovoltaic device of the concrete example of the present invention, experimental result shows Generate a photovoltaic voltage of approximately 80 mV. In addition, when the photovoltaic device of the specific example of the present invention is irradiated with 632nm visible light, the generated photovoltaic voltage is almost indistinguishable.

To sum up, the working principle of the photovoltaic device provided by the present invention is completely different from the photovoltaic devices of the prior art. The photogenerated carriers in the optical gain semiconductor material are quickly transferred to the metal electrode and graphene, and a Fermi level difference is established at both ends of the graphene electrode, thereby realizing the photovoltaic effect. Under short-circuit conditions, ultrafast response and sensitive detection of irradiated light can be achieved due to the excellent electron transport properties of graphene. Therefore, the photovoltaic device of the present invention can be used as an ultrafast, sensitive photodetector that does not require a power source.

In addition, the high-resistance light-gain semiconductor material of the photovoltaic device of the present invention can be an organic semiconductor or an inorganic semiconductor thin film material, and the selection range is wide; the choice of the metal electrode material is large; the device process of the photovoltaic device is simple, the size is small, and it is different from the existing Large-scale integrated circuits have good process compatibility and low manufacturing costs.

Although the present invention has been described in terms of preferred embodiments, the present invention is not limited to the embodiments described herein, and various changes and changes are included without departing from the scope of the present invention.

Claims (13)

1. a kind of photovoltaic devices, including light source and photovoltaic device, the photovoltaic device includes high resistance light gain semi-conductor substrate, position Continuous graphene layer on the high resistance light gain semi-conductor substrate, positioned at the high resistance light gain semi-conductor substrate and institute The first electrode and second electrode on graphene layer are stated, wherein, a part for the first electrode and the high resistant gain of light half Conductor substrate contact, another part contact with the graphene layer, a part for the second electrode and the high resistant gain of light Semiconductor substrate contacts, and another part contacts with the graphene layer, wherein, the energy of the light of the light source transmitting is more than described The band gap of high resistance light gain semi-conductor substrate.

2. photovoltaic devices according to claim 1, it is characterised in that：The high resistance light gain semi-conductor substrate has for high resistant Machine semiconductor or high resistant inorganic semiconductor.

3. photovoltaic devices according to claim 1, it is characterised in that：The high resistance light gain semi-conductor substrate is single piece Body or the semi-insulating film being grown on substrate.

4. photovoltaic devices according to claim 1, it is characterised in that：The light source is ultraviolet source, and the high resistance light increases Beneficial Semiconductor substrate is SiC, or the light source is visible light source, and the high resistance light gain semi-conductor substrate is GaP or GaAs.

5. photovoltaic devices according to any one of the preceding claims, it is characterised in that：The high resistance light gain semi-conductor The thickness of substrate is more than 50nm.

6. photovoltaic devices according to claim 1, it is characterised in that：The graphene layer is in the first electrode and described Length between second electrode is more than 3 μm.

7. photovoltaic devices according to claim 1, it is characterised in that：The first electrode and the second electrode are metal Electrode.

8. photovoltaic devices according to claim 7, it is characterised in that：The electronic work function of the metal electrode and the height The difference of the electronic work function of light blocking gain semi-conductor substrate is more than 0.1eV.

9. the photovoltaic devices according to claim 7 or 8, it is characterised in that：The first electrode and the second electrode are adopted With identical metal.

10. photovoltaic devices according to claim 9, it is characterised in that：Also include the first electrode or described second Lighttight coat on electrode.

11. photovoltaic devices according to claim 1, in addition to it is respectively electrically connected to the first electrode and second electricity The first lead and the second lead of pole.

12. photovoltaic devices according to claim 11, in addition to by the high resistance light gain semi-conductor substrate, the graphite The encapsulating housing that alkene layer, first and second electrode and first and second lead are packaged, wherein the encapsulation Housing has thang-kng window.

13. a kind of method for producing photovoltaic effect, including light irradiation photovoltaic device is used, the photovoltaic device includes high resistance light Gain semi-conductor substrate, the continuous graphene layer on the high resistance light gain semi-conductor substrate, positioned at the high resistance light Gain semi-conductor substrate and first electrode and second electrode on the graphene layer, wherein, a part for the first electrode With the high resistance light gain semi-conductor substrate contact, another part contacts with the graphene layer, one of the second electrode Divide and contacted with the high resistance light gain semi-conductor substrate contact, another part with the graphene layer, methods described includes：Use it The light source that the energy of light is more than the band gap of the high resistance light gain semi-conductor substrate irradiates the photovoltaic device.