CN103413894A - Transparent solar cell with polarization absorption function - Google Patents

Abstract

The invention discloses a polarized absorption transparent solar cell, which includes a substrate, a solar cell body and an encapsulation layer. The solar cell body is composed of a transparent anode film layer, a photoelectric conversion layer and a transparent cathode film layer. The photoelectric A metal grating is embedded in the conversion layer. The invention provides a polarized absorption transparent solar cell. Due to the plasma enhancement effect of the metal grating embedded in the photoelectric conversion layer, the number of photons absorbed per unit area of the photoelectric conversion layer is increased by 45.3% compared with the traditional transparent solar cell; At the same time, due to the introduction of the grating structure, the electrode-to-carrier collection area is enlarged, the internal quantum efficiency of the device is improved, and a higher photoelectric conversion efficiency is realized.

Description

A polarized absorbing transparent solar cell

technical field

The invention belongs to the field of solar cells, in particular to a polarized absorption transparent solar cell.

Background technique

In the past 50 years, the energy consumption rate of human society has increased rapidly. Since today's energy mainly comes from thermal power generation, this has directly led to a rapid decline in the reserves of non-renewable energy such as coal, oil, and natural gas on the earth. On the one hand, due to the limited reserves of the above-mentioned energy sources, they cannot be supplied to human society for a long time; on the other hand, the destruction of the ecological environment due to the burning of fossil fuels will have an immeasurable negative impact on the earth's ecology. In order to solve the energy problem, the development of new renewable clean energy is an important and urgent work. Solar energy is an important renewable energy source and the only inexhaustible clean energy source available to human beings.

At present, the development and utilization of solar energy are mainly divided into thermal energy utilization and light energy utilization. Solar thermal energy utilization refers to the use of sunlight to heat water to generate steam to use its internal energy; light energy utilization refers to the use of solar cells to convert solar energy into electrical energy. Make use of. Because electric energy is easier to store and transport, converting solar energy directly into electric energy is more conducive to the comprehensive utilization of solar energy. Therefore, solar cells have become a research and development hotspot in various countries in recent decades.

A solar cell, also known as a "solar chip" or a "photovoltaic cell", is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. But because ordinary solar cells need to absorb visible light, they are mostly black, which greatly limits their scope of use. At present, the newly developed transparent solar cell can improve this shortcoming of ordinary solar cells and expand its application range.

The absorption windows of transparent solar cells are mainly concentrated in the ultraviolet band, infrared band and a small amount of visible band. phone screen etc.

Using transparent solar cells as glass curtain walls will not block people's sight, but also can use the absorbed invisible light for power generation, saving energy. The currently developed transparent solar cells can achieve a photoelectric conversion efficiency of 2% and a transparency of 70%. Therefore, how to further improve the photoelectric conversion efficiency is the focus of current research.

When the ordinary polarizing element receives the incident light and realizes the polarization function, most of the incident light will be lost through reflection or other forms, which will cause a large waste of energy. For example, in the liquid crystal display (LCD) technology that is most used today, since the backlight in the LCD needs to be polarized to work, but about 75% of the light energy in the polarized original will be reflected and other forms can not be output eventually, This leads to a huge waste of light sources.

Therefore, it will be of great practical significance to find a method to realize the absorption and utilization of other incident light and reduce energy waste while realizing the polarization function.

Contents of the invention

The invention provides a polarized absorption transparent solar cell, which utilizes its internal metal grating structure to generate plasma enhancement, and improves the photoelectric conversion efficiency of the transparent solar cell without affecting its visible light transmittance.

A polarized absorption transparent solar cell is composed of a substrate, a solar cell main body and an encapsulation layer. The solar cell main body is composed of a transparent anode thin film layer, a photoelectric conversion layer and a transparent cathode thin film layer, and a metal grating is embedded in the photoelectric conversion layer.

First define the polarization direction of the incident light (as shown in Figure 2):

The polarization direction is parallel to the period direction of the grating, which is defined as the TE direction;

The direction perpendicular to the period of the grating is defined as the TM direction.

Natural light can be decomposed into two beams of polarized light whose polarization directions are perpendicular to each other. The polarized absorption transparent solar cell of the present invention embeds a metal grating inside the photoelectric conversion layer, and the electromagnetic field around the grating structure resonates with a certain polarization component of the incident natural light. Since we use a planar grating, a certain polarization component is the TE polarization component. When the electromagnetic field resonates with the TE polarization component, a large plasmon enhancement will be generated. This plasmon near-field enhancement will be coupled into the photoelectric conversion layer material, increasing The absorption intensity of the TE polarization component is improved, but the light intensity of the TM polarization component has little influence, so a high transmittance can be maintained for the TM polarization component, thereby realizing polarization absorption (transmission).

Different metals correspond to different plasmonic excitation wavelengths, so by choosing different metals, the polarization absorption of a certain wavelength band of light can be realized. Preferably, the metal material used in the metal grating is silver (Ag), gold (Au) or aluminum (Al), more preferably, the metal material is silver. Compared with the other two metals, metallic silver can excite stronger plasmon enhancement in the visible light spectrum by preparing appropriate metal structure and size, and the light absorption intensity in this band is greatly improved; and the price of metallic silver is relatively low, Adapted to commercial applications.

Preferably, the grating period of the metal grating is 50nm-400nm. The period of the grating varies with different photoelectric conversion materials and metals, and the period needs to be optimized to achieve the best absorption intensity. Further preferably, when silver (Ag) is used as the metal, the grating period is 175 nm, and at this time, the light absorption intensity of the photoelectric conversion layer reaches the best.

The grating duty cycle is the ratio of the grating width to the grating period, and its value has a great influence on the polarization absorption performance. If the duty cycle is too large, it will affect the light transmittance. If the duty cycle is too small, the excited plasmon enhancement range will be small, which will affect the optical absorption. By selecting the appropriate duty cycle to excite the appropriate wavelength enhancement without affecting the transmittance. Preferably, the grating duty ratio of the metal grating is 0.1-0.8. According to different photoelectric conversion materials and different metals, the duty ratio needs to be optimized to achieve the best absorption intensity. Further preferably, when silver (Ag) is used as the metal, its duty ratio is 0.14. Selecting this duty cycle can stimulate the wavelength enhancement of visible light without affecting the transmittance.

Preferably, the metal grating has a grating height of 10 nm to 150 nm. A grating that is too thick will affect the light transmittance of the device, while a grating that is too thin stimulates plasmonic enhancement with limited intensity and range. According to different photoelectric conversion materials, as well as different metals, the grating height needs to be optimized to achieve the best absorption intensity. Further preferably, when silver (Ag) is used as the metal, the grating height is 65nm, at this time, the light absorption intensity of the photoelectric conversion layer reaches the best.

The photoelectric conversion layer of a solar cell includes a donor material and an acceptor material. The photoelectric conversion layer, that is, the functional layer can be a single-layer bulk heterojunction functional layer blended with a donor material and an acceptor material, or a donor and an acceptor material. The receptors are respectively formed into a double-layer heterojunction functional layer.

In transparent solar cells, the absorption coefficient of the donor and acceptor materials in the visible light region is required to be small, and the main absorption wavelength ranges are the ultraviolet band (about 200nm ~ 400nm) and the infrared band (greater than 750nm), so as to ensure the protection of visible light. High transmittance, while absorbing ultraviolet rays and heat insulation. Preferably, the donor material is Chloroaluminum phthalocyanine (ClAlPc), whose absorption band is mainly in the infrared band; preferably, the acceptor material is generally fullerene C ₆₀ , C ₇₀ , Derivatives of fullerene or 6,6-phenyl-C71-butyric acid methyl ester (PCBM-C ₇₀ ), more preferably, the acceptor material is fullerene C ₆₀ , so far, fullerene is still It is recognized as the best electron acceptor material. On the one hand, it is due to the short photoconductive charge conversion time between it and the electron donor, which is only about 50 fs; on the other hand, fullerene can achieve high electron mobility.

The material of the transparent anode film layer requires high transmittance in the full spectrum or most of the spectrum of sunlight, and can be a single-layer structure or a composite structure composed of an anode and an anode buffer layer. The introduction of the buffer layer better modified the interface between the electrode and the photoelectric conversion layer, and at the same time made the energy levels of the two more matched.

Preferably, the material of the single-layer anode film layer is indium tin oxide (ITO), a transparent conductive film with high conductivity. The ITO electrode has good permeability, which allows the incident light to pass through the electrode and irradiate the photoelectric conversion layer. It is the best choice for the transparent solar cell electrode; at the same time, the preparation process of ITO is mature and has a strong substrate. of adhesion.

Preferably, the anode buffer layer is a polymer anode buffer layer. Further preferably, the polymer anode buffer layer can use low-conductivity PEDOT:PSS or 2,9-dimethyl-4,7-biphenyl-1,10-phenanthroline (bathocuproine, BCP) . Among them, PEDOT is a polymer of 3,4-ethylenedioxythiophene monomer (DOT), and PSS is polystyrene sulfonate. These two anode buffer layers have been widely used and have good hole injection properties.

The material of the transparent cathode thin film layer is also required to have high transmittance in the full spectrum of sunlight or most of the spectral range, and can be a single-layer structure, or a composite structure of the cathode and the cathode buffer layer.

Preferably, the material of the single-layer cathode film layer is indium tin oxide (ITO), a transparent conductive film with high conductivity.

Preferably, the cathode buffer layer material is generally a metal compound, more preferably molybdenum oxide (MoO ₃ ), and molybdenum oxide has been proven to have good performance in improving the energy level matching between the electrode and the photoelectric conversion layer.

The transparent solar cell substrate requires a wide transmittance spectrum, especially high transmittance to ultraviolet and infrared light. Preferably, the substrate is quartz glass.

The encapsulation layer requires high transmittance and high density. As a preference, the encapsulation layer is traditional transparent ethylene-vinyl acetate copolymer (EVA)-glass, which can be laminated by vacuum heating. The polarized absorption transparent solar cell is packaged.

The polarized absorption transparent solar cell main body is on the substrate, and from bottom to top, it can be a transparent anode thin film layer, a photoelectric conversion layer and a transparent cathode thin film layer, or it can be a transparent cathode thin film layer, a photoelectric conversion layer and a transparent cathode thin film layer in sequence. Anode film layer.

Compared with traditional transparent solar cells, the polarization-absorbing transparent solar cells of the present invention have the following unique advantages in addition to inheriting the advantages of high visible light transmittance, UV protection, and heat insulation:

The polarized absorption transparent solar cell prepared by the present invention, due to the plasmonic enhancement effect of the metal grating embedded in the photoelectric conversion layer, the number of photons absorbed per unit area of the photoelectric conversion layer is increased by 45.3% compared with the traditional transparent solar cell; the grating The structure also increases the contact area between the photoelectric conversion layer and the electrode, resulting in greater internal quantum efficiency, and the photoelectric conversion efficiency of the cell is proportional to the product of the number of absorbed photons and the internal quantum efficiency, so it has a higher photoelectric conversion efficiency.

The polarized-absorbing transparent solar cell prepared by the present invention is used to replace the ordinary polarizing element, and the polarized-absorbed transparent solar cell can ensure a higher transmittance for the output polarization component; at the same time, the solar cell will be reflected Or other reasons, the polarization component that cannot be output finally and the invisible spectrum in the light source are absorbed, and converted into electrical energy, which improves the utilization rate of energy.

Description of drawings

Fig. 1 is the structural representation of the polarized absorption solar cell of the present invention;

Fig. 2 is the sectional structure diagram of the solar cell main body of polarized absorption of the present invention;

Fig. 3 is the solar cell transmittance spectrogram of polarized absorption of the present invention;

Fig. 4 is a dichroic ratio spectrum diagram of the polarized absorption solar cell of the present invention.

Detailed ways

Example

As shown in Fig. 1, the polarized absorption solar cell of the present invention is composed of an EVA-glass encapsulation layer (101), a transparent solar energy body (102), and a transparent quartz glass substrate (103). Concrete preparation steps are as follows:

1. First prepare the transparent cathode film layer (104), wipe the transparent quartz glass substrate (103) with a non-woven cloth to ensure that it is dust-free, and then coat a layer of ITO conductive film on the surface of the substrate by sputtering, with a thickness of 100nm ~ 180nm.

Then, a layer of molybdenum oxide film is deposited on the surface of the ITO conductive film by thermal evaporation as a cathode buffer layer. The evaporation rate is controlled at 0.1-0.5nm/s, and the thickness is controlled at 15nm-25nm.

2. Continue to prepare the photoelectric conversion layer (105) on the surface of the cathode film layer (104) prepared in step 1, and form a donor layer on the surface of the cathode film layer by thermal evaporation, which is an aluminum phthalocyanine chloride film layer, The evaporation rate is controlled below 0.2nm/s, and the thickness is controlled between 15nm and 20nm; then a layer of C ₆₀ thin film is formed on the donor layer by thermal evaporation as the acceptor layer, and the evaporation rate is controlled below 0.2nm/s, and the thickness is controlled below 0.2nm/s. Controlled at 25nm to 40nm; on the surface of the acceptor layer, a grating mask is first formed by traditional nanoimprint technology, the material of the mask is polydimethylsiloxane (PDMS), and then evaporated by electron beam Evaporating metallic silver, and finally transferring the formed metallic silver grating (105) onto the photoelectric conversion layer. The width (w), height (h) and period (p) of the metallic silver grating are 25nm, 65nm and 175nm respectively.

3. Continue to prepare a transparent anode film layer (106) on the surface of the photoelectric conversion layer prepared in step 2. First, form a layer of BCP film by thermal evaporation, with a thickness of 5nm-10nm and an evaporation rate of 0.1-0.5nm/s ; Then, a layer of ITO conductive film is plated on the BCP film by sputtering, the thickness is controlled at 100nm-150nm, and the coating speed must be very slow, controlled at 0.005nm-0.03nm/s.

4. Finally, using ethylene-vinyl acetate copolymer (EVA)-glass as the encapsulation layer, the encapsulation layer is bonded to the main body of the transparent solar cell by vacuum heating lamination, and the polarized absorption transparent solar cell is prepared .

A periodic cross-sectional structure of the polarization-absorbing solar cell body (102) of the present invention is shown in Figure 2, consisting of a transparent anode thin film layer (104), a photoelectric conversion layer (105), and a transparent cathode thin film layer (106). The transparent anode thin film layer (104) includes an ITO layer (107) with high transmittance and high conductivity and an ultra-thin molybdenum oxide layer (108); the photoelectric conversion layer (105) is a double-layer film formed of a donor and an acceptor respectively The heterojunction functional layer, the donor layer (109) is aluminum phthalocyanine chloride, the acceptor layer (110) is fullerene C ₆₀ ; the transparent cathode film layer (106) includes an ultra-thin BCP layer (111) and a high light transmittance over-rate and high-conductivity ITO layer (112). The metal grating layer (113) is embedded in the acceptor layer (110), and the material is metallic silver (Ag).

comparative example

In this comparative example, a transparent solar cell without a metal grating was prepared, and the specific preparation steps are as follows:

1. First prepare the transparent cathode film layer, wipe the transparent quartz glass substrate with non-woven cloth to ensure dust-free, and then coat a layer of ITO conductive film on the surface of the substrate by sputtering, with a thickness of 100nm to 180nm, and then A molybdenum oxide film is deposited on the surface of the ITO conductive film by thermal evaporation as a cathode buffer layer, the evaporation rate is controlled at 0.1-0.5nm/s, and the thickness is controlled at 15nm-25nm.

2. Continue to prepare a photoelectric conversion layer on the surface of the cathode film layer prepared in step 1, and form a donor layer on the surface of the cathode film layer by thermal evaporation, which is an aluminum phthalocyanine chloride film layer, and the evaporation rate is controlled at 0.2nm /s or less, the thickness is controlled at 15nm to 20nm; and then a layer of C ₆₀ thin film is formed on the donor layer as the acceptor layer by thermal evaporation, the evaporation rate is controlled below 0.2nm/s, and the thickness is controlled at 25nm to 40nm.

3. Continue to prepare a transparent anode thin film layer on the surface of the photoelectric conversion layer prepared in step 2. First, a layer of BCP film is formed by thermal evaporation, the thickness is controlled at 5nm-10nm, and the evaporation rate is controlled at 0.1-0.5nm/s; The method of sputtering coats a layer of ITO conductive film on the BCP film, the thickness is controlled at 100nm-150nm, and the coating speed must be very slow, controlled at 0.005nm-0.03nm/s.

4. Finally, using ethylene-vinyl acetate copolymer (EVA)-glass as the encapsulation layer, the encapsulation layer was bonded to the main body of the transparent solar cell by vacuum heating lamination, and a transparent solar cell without metal grating was prepared.

Performance and Application

Under the standard solar spectrum (i.e. AM1.5 spectrum), refer to the comparison of photon absorption per unit area between transparent solar cells and polarized absorption solar cells, as shown in Table 1. Visible TE waves and TM waves, both of which have polarized incident light absorption Enhanced. The overall average increase in absorption is 45.3%. Due to the introduction of the grating structure, the expansion of the electrode-to-carrier collection area will increase the internal quantum efficiency of the device to a certain extent, and the conversion efficiency of the battery is proportional to the product of the number of absorbed photons and the internal quantum efficiency, so the device’s The photoelectric conversion efficiency will be more greatly improved.

Table 1

The number of photons absorbed per unit area/piece comparative example Example improve/% TE wave 3.86×10 ²⁰ 6.69×10 ²⁰ 73.3 TM wave 3.86×10 ²⁰ 4.87×10 ²⁰ 26.2 average value 3.86×10 ²⁰ 5.48×10 ²⁰ 45.3

Fig. 3 is the transmittance curve of the transparent solar cell of the embodiment and the comparative example, wherein, 31 is the transmittance curve of the transparent solar cell without the metal grating of the comparative example, no metal grating is introduced in the comparative example, so the transparent solar cell There is no polarized absorption feature, and the transmittance in the visible light range is between 60% and 70%; 33 is the transparent solar cell with polarized absorption in the embodiment, the transmittance curve of the incident light with TM polarization, and the transmittance decreases Not much, the phenomenon of polarization absorption is not obvious, and a small amount of reflection will occur due to the existence of the metal grating, but the overall transmittance is still 50% to 60%. 32 is the polarized absorption transparent solar cell of the embodiment, the transmittance curve of its TE polarized incident light, the transmittance in this curve has a large drop, reaching the minimum at 630nm, this is because near this wavelength A strong plasmonic enhancement effect will be excited, resulting in strong absorption of light energy near this wavelength.

A further analysis of the polarized absorption solar cell transmits the difference between the two polarized light, and introduces the concept of dichroic ratio, that is, the ratio of TM and TE polarized light transmittance, as shown in Figure 4, the visible wavelength is 630nm Nearby, the dichroic ratio reaches a maximum of 6.7.

As shown in Figure 3 and Figure 4, the polarization-absorbing transparent solar cell of the present invention has the characteristics of polarization absorption, can replace ordinary polarizing elements, and convert the received light energy into electrical energy while realizing the polarization function, realizing Energy reuse.

For the above-mentioned characteristics of the polarized absorption transparent solar cell of the present invention, the following two application fields are proposed:

1) The polarized absorption transparent solar cell of the present invention is used to replace the filters on car windows and lights. For example, the filters of car lights only pass TE light, so the outgoing light is TE light, while the front windshield The window filter only passes the TM light perpendicular to the TE light, so that the oncoming car light pair will not pass through the front windshield. Reducing the stimulation of the driver by the light of the incoming car can play a role in anti-glare and improve driving safety. At the same time, it can convert the light energy generated by absorbing the light of the incoming car into electrical energy for charging the battery of the car.

2) Replace the polarizing element in the liquid crystal display (LCD) with the polarization-absorbing transparent solar cell of the present invention. Since the backlight in the LCD needs to be polarized to work, about 75% of the light energy in the polarizing element will pass through Reflection and other forms are ultimately not output. The polarization-absorbing transparent solar cell replaces the original polarizing element. Due to its polarization-absorbing characteristics, it can absorb part of the component perpendicular to the polarization of the output light (originally reflected light), and the invisible spectrum of the light source includes ultraviolet and infrared components. The battery absorbs the light energy and converts it into electrical energy to reduce energy waste. At the same time, for the required output polarization component, the solar cell of the present invention can still maintain a relatively high transmittance.

Claims (7)

1. the transparent solar cell of a polarization absorption, comprise substrate, solar-electricity tank main body and encapsulated layer, described solar-electricity tank main body consists of transparent anode thin layer, photoelectric conversion layer and transparent cathode thin layer, it is characterized in that, is embedded with metal grating in described photoelectric conversion layer.

2. the transparent solar cell of polarization absorption as claimed in claim 1, is characterized in that, the material of described metal grating is silver, gold or aluminium.

3. the transparent solar cell of polarization absorption as claimed in claim 2, is characterized in that, the material of described metal grating is silver.

4. the transparent solar cell of polarization absorption as claimed in claim 1 or 2, is characterized in that, the grating cycle of described metal grating is 50nm～400nm.

5. the transparent solar cell of polarization absorption as claimed in claim 4, is characterized in that, the grating duty ratio of described metal grating is 0.1～0.8.

6. the transparent solar cell of polarization absorption as claimed in claim 4, is characterized in that, the grating height of described metal grating is 10nm～150nm.

7. the transparent solar cell of polarization absorption as claimed in claim 1, it is characterized in that: described photoelectric conversion layer comprises donor material and acceptor material, and described donor material is phthalocyanine aluminium chloride, and described acceptor material is fullerene C ₆₀.

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