High-efficiency ultrathin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode

Abstract

The invention discloses a high-efficiency ultrathin GaAs solar cell based on photonic crystals and ITO / Ag / ITO transparent electrodes, which is characterized in that the bottom layer is an Al substrate, the second layer is an AlGaAs photonic crystal, the structure of the AlGaAs photonic crystal is a tetragonal lattice, the lattice constant is a, the radius of a cylinder is R, the thickness of the cylinder is h, the AlGaAs photonic crystal is wrapped by SiO2, the third layer uses Al0. 3Ga0. 7As as an electron transport layer, the fourth layer is a GaAs absorption layer, and the fifth layer is a GaAs transparent electrode. The fifth layer uses Al < 0.75 > Ga < 0.25 > As as a hole transport layer, and the top layer is a SiO2 and ITO / Ag / ITO transparent electrode. The solar cell with the structure has the characteristics of small volume and high light absorption and photoelectric conversion efficiency.

Description

Technical Field

[0001] The invention relates to the field of optical communication technology, and in particular to constructing an ultra-thin GaAs solar cell structure by utilizing photonic crystals and ITO / Ag / ITO multilayer electrodes with excellent performance. Background Art

[0002] Photonic crystals (PC) are a class of materials with periodic changes in dielectric constants. Through their unique structural characteristics, the propagation behavior of photons can be effectively controlled. The basic principle of photonic crystals is similar to the electronic band structure in semiconductors. The periodic structure is used to form optical "bands" in space, thereby generating photonic band gaps in certain frequency ranges, that is, light of a certain frequency cannot propagate in the crystal. This characteristic makes photonic crystals have great potential in manipulating the transmission, reflection and transmission of light. Localized surface plasmons (LSPs) are localized electron oscillations on the surface of metal nanoparticles caused by light excitation. This oscillation is confined to the surface of the nanoparticles and produces a strong local electromagnetic field enhancement effect.

[0003] APL Materials published the article "Ultrathin and easy-processing photonic crystal absorbing layers to enhance light absorption efficiency of solar cells". Wan's team used hexagonal columnar scatterers and discussed the filling of air and silicon dioxide respectively. The study found that the photonic crystal structure can significantly improve the absorption rate of the battery absorption layer. Energies published the article "Application of TiO2 / Ag / TiO2 as an Ohmic Contact to an AlGaAs Layer in a GaAs Solar Cell". Vitanov's team used nano-layered TiO2 / Ag / TiO2 structure as a transparent conductive coating on GaAs solar cells and found that this structure can form an ohmic contact on the AlGaAs window layer with excellent optical and electrical properties. However, although the methods proposed in the above studies can effectively improve the performance of solar cells, the photoelectric conversion efficiency of the battery is not ideal, which is severely limited by the Shockley-Queisser limit. Summary of the invention

[0004] The purpose of the present invention is to design an ultra-thin GaAs solar cell structure by analyzing and selecting the light absorption rate and photovoltaic performance of solar cells in view of the deficiencies of the prior art. The structure adopts a dual strategy of front-end ITO / Ag / ITO transparent electrodes and back-end photonic crystals, so that the absorption rate of GaAs solar cells with an absorption layer thickness of only 500nm in the visible light range reaches more than 95%, and the final photoelectric conversion efficiency reaches 35.12%. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 It is a schematic diagram of the battery model structure; DETAILED DESCRIPTION

[0006] The content of the present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0007] Reference Figure 1 , a high-efficiency ultra-thin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode, wherein the bottom layer is Al substrate 1, the second layer is AlGaAs photonic crystal 2, the structure of which is a tetragonal lattice, the lattice constant is a, the radius of the cylinder is R, the thickness is h, it is wrapped by SiO2, and the third layer is Al 0.3 Ga 0.7 As electron transport layer 3, the fourth layer is GaAs absorption layer 4, and the fifth layer is Al 0.75 Ga 0.25 As hole transport layer 5, the top layer is SiO2 and ITO / Ag / ITO transparent electrode 6, in which the Ag nanoparticle array is embedded in the middle of ITO, with a radius of 25nm and a period of 80nm.

[0008] The Al substrate 1 is used as the back electrode of the battery and has a thickness of 100 nm.

[0009] The AlGaAs photonic crystal 2 is used as the back reflection layer of the battery, and its lattice constant a is 450nm, the dielectric column radius R is 120nm, and h is 130nm. This structure has two clear TE photon band gaps at a normalized frequency of 0-0.74, which can modulate the spectral range and localize photons, thereby improving the light absorption and photoelectric conversion efficiency of the battery.

[0010] The Al 0.75 Ga 0.25 As and Al 0.3 Ga 0.7As is used as the hole transport layer 5 and the electron transport layer 3 of the battery, and the thickness of each layer is 50nm. Since AlGaAs can change the band structure by adjusting the Al content, the band gap difference between AlGaAs and GaAs can be adjusted, which is beneficial to control the transport and life of carriers. In addition, AlGaAs and GaAs have similar lattice constants. This lattice matching helps to reduce lattice defects and interface states, and improve the performance and stability of the device.

[0011] The GaAs is used as the absorption layer 4 of the battery, and its thickness is 500nm.

[0012] The SiO2 and ITO / Ag / ITO transparent electrodes are used as the top 6 of the battery, and their thicknesses are 50nm and 100nm respectively. SiO2 can reduce surface reflection, increase the incidence of light, and prevent oxidation and corrosion of electrode materials, thereby improving the durability of the device. The ITO / Ag / ITO structure has excellent transparency and conductivity. As a transparent electrode, it can realize transparent transmission of light and effective conduction of charges. Ag nanoparticles can also excite LSPs under the action of incident light, thereby jointly improving the photoelectric conversion efficiency and stability of the solar cell.

[0013] In this case, when sunlight hits the surface of the battery, photons are absorbed by the GaAs absorption layer, generating electron-hole pairs. Under the action of the built-in electric field of the pn junction, these electrons and holes are separated and move to the n-type and p-type regions respectively. The top SiO2 anti-reflection layer reduces reflection, the ITO / Ag / ITO transparent electrode improves light transmission and charge collection efficiency, the Ag nanoparticles stimulate the surface plasmon effect to enhance light absorption, the AlGaAs photonic crystal structure increases the localization and reflection of light, extends the path of light in the absorption layer, and the optimized pn junction doping concentration improves the efficiency of carrier generation and separation. Finally, the separated electrons and holes enter the external circuit through the electrode to form a current, achieving efficient photoelectric conversion.

Claims

1. A high-efficiency ultra-thin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode, characterized in that: The bottom layer is Al substrate 1, the second layer is AlGaAs photonic crystal 2, which has a tetragonal lattice structure, a lattice constant, a cylinder radius R, a thickness h, and is wrapped by SiO2. The third layer is Al 0.3 Ga 0.7 As electron transport layer 3, the fourth layer is GaAs absorption layer 4, and the fifth layer is Al 0.75 Ga 0.25 As hole transport layer 5, the top layer is SiO2 and ITO / Ag / ITO transparent electrode 6.

2. The high-efficiency ultra-thin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode according to claim 1, characterized in that: The AlGaAs photonic crystal 2 has a lattice constant a of 450 nm, a radius R of 120 nm, and a thickness h of 130 nm.

3. The high-efficiency ultra-thin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode according to claim 1, characterized in that: The Ag nanosphere array in the ITO / Ag / ITO transparent electrode is embedded in the middle of the ITO, with a period of 80nm and a radius of 25nm.

4. The high-efficiency ultra-thin GaAs solar cell based on photonic crystal and ITO / Ag / ITO transparent electrode according to claim 1, characterized in that: The P-type doping concentration and the N-type doping concentration in the GaAs absorption layer 4 are both 2×10 19 cm -3 .

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