(1) Improve the original preparation process and develop new processes to increase the output of silicon raw materials
At present, there are reports on some new process methods: vapor to liquid deposition (VLD) and molten silicon refinement. In the VLD method, trichlorosilane (SiHC3) and hydrogen (H2) are injected together into a graphite tube at 1500°C to form silicon fused deposition, which is faster than the traditional Siemens method. Future research will develop more new processes and increase silicon output.
(2) Looking for new materials
Researchers have found that semiconductors such as nitrided steel have a band gap that is significantly smaller than originally thought, lower than 0.7 eV. This finding indicates that photovoltaic cells based on alloys containing chromium, ions, and nitrogen will be sensitive to radiation in all solar spectra. This alloy can be used to develop relatively cheap solar panels, and the new solar panels will be stronger and more efficient than the existing ones. Relevant personnel pointed out that multi-level solar cells made of nitrided steel and nitrided double-layer can reach 50% of the theoretical maximum efficiency. For this reason, one layer needs to be “adjusted” to a band gap of 1.7eV, and the other The layer needs to be “adjusted” to the forbidden band of 1.leV. If solar cells with many layers can be made, and each layer has its own band gap, the maximum theoretical efficiency of solar cells can reach more than 70%. Researchers at Oregon State University and Portland State University in the United States have experimentally confirmed that a tiny seaweed called “diatom” helps to make dye-sensitized solar cells ( The power output of dye-sensitized solarcel1) is increased by 3 times. By capturing the light in the nano-pores of the thin-film solar cell covered with the diatom layer, the cell can obtain more incident photons, thereby greatly improving the power generation efficiency. In the system, photons bounce in the small holes formed by the diatom shell, which can increase its energy efficiency by 3 times compared with traditional systems.
Graphene is an ideal conductive electrode material for solar cells. By introducing graphene materials into solar cells, the photoelectric conversion efficiency of solar cells is effectively improved. Graphene can be used as a nano-coating, coated on the surface of the device to obtain the ability of photoelectric conversion. It can also be made into flexible and transparent solar panels. Therefore, in the future, equipment with solar power will be more compact and beautiful, and at the same time, the product design can be changed without being affected by the solar panel itself. Graphene coating can use common materials such as glass and plastic as the substrate, so it can be coated on the surface of digital products. For example, the screen of a mobile phone, the shell of a laptop, etc. The photoelectric conversion efficiency of graphene solar technology is as high as 60%, which is twice that of the existing crystalline silicon solar technology. The report pointed out that graphene has been regarded as one of the best candidates for building third-generation solar cells.
(3) Reduce reflection loss
It is possible to use anti-reflection film on the illuminated surface, surface etching to reduce reflection, increase the optical path of light in the battery and back reflection film and other measures.
The following two techniques are generally used: ① Using anti-reflection film. Commonly used anti-reflection films include silicon oxide (SiO) and titanium oxide (TiO) with an oxygen content of 1 to 2. The effect of using a single layer of reflective film alone is not good. For this reason, two layers of anti-reflection film are mostly used, such as an anti-reflection film composed of TiO2 and MgF2 or an anti-reflection film composed of SiN and SiO2. The surface of the solar cell after anti-reflection treatment has a good anti-reflection effect. ②Using concave-convex structure. For example, the surface is treated with a method such as etching to have a lot of pyramid-shaped suede-like structures or an inverted pyramid-shaped groove structure, or a V-shaped groove structure. The incident sunlight from various directions can enter the solar cell after multiple reflections, thereby increasing the amount of incident sunlight. With this structure, some of its light reflection loss can even be reduced to about 5%. The reflectivity of the untreated smooth silicon surface is generally as high as about 30%.
(4) Surface passivation technology
The surface passivation of crystalline silicon solar cells has always been the top priority of design and optimization. It has experienced the only back electric field passivation in the early stage, the front silicon nitride passivation, and the PERC/PERL design of passivating partial opening contacts with dielectric layers such as silicon oxide, aluminum oxide, and silicon nitride introduced on the back. Although this structure temporarily alleviates the problem of back passivation, it has not been eradicated. The high recombination rate at the openings still exists, and the process is further complicated. In recent years, a technology that can achieve passivation of the entire back surface without opening contacts has become a hot spot for institutional research, which is the passivated contact technology. When both sides of the battery adopt passivation contacts, it is also possible to realize a selective contact (selective contact) battery structure without a diffused PN junction.
(5) Reduce transmission loss
The Massachusetts Institute of Technology research team composed of American physicists and engineers successfully added an anti-reflection coating on the front side of the ultra-thin silicon film that constitutes solar cells, and added a multilayer reflective film and diffraction grating on the back side. The fine structure of the combination. The longer the transmission distance in the silicon film means the higher the probability of light energy being absorbed, and the absorbed light energy will cause the free electrons in the film to form an electric current. This is enough to allow the light irradiated into the film to be reflected in the film for a longer period of time, so that there is sufficient time for the light energy to be absorbed and converted into electrical energy, resulting in a 50% increase in the electrical output of the solar cell.
(6) Adopt nanostructure
It is a feasible choice to use nanostructures such as multiple quantum wells and quantum dots as the intrinsic layer to improve the collection efficiency of photogenerated carriers and the light excitation characteristics. It is reported that quantum dots of certain semiconductor materials can release more than two photons when they are bombarded by high-energy photons such as blue and ultraviolet rays from the end of the spectrum. Although the conversion efficiency of nanostructured solar cells currently developed by people is relatively low, it is theoretically estimated that if the interface characteristics of quantum dots are further adjusted and the electron transmission process between dots is improved, then photovoltaic modules based on quantum dot technology will have the highest The efficiency can reach 42%, which is much higher than the theoretical 31% efficiency of crystalline silicon solar cells. L.Raniero et al. fabricated a nanostructured solar cell with nc-Si:H intrinsic layer, and obtained an open circuit voltage of 0.95V, a short-circuit current density of 14.96mA/cm², a fill factor of 0.67 and a conversion efficiency of 9.52%.
(7) Cascaded solar cells
Cascaded solar cells are the integration of sub-cells made of semiconductor materials with different spectral responses, making full use of the wavelengths of the solar spectrum. Solar radiation can improve the utilization rate through multi-junction cell technology, such as the triple junction cascade cell composed of GalnP/Ga(In)As/Ge, which is a kind of cascade solar cell that has been used at present, and the products are used in space and ground Concentrating photovoltaic systems, however, this three-junction cascade cell structure cannot make full use of the infrared part of sunlight beyond 880nm. It is hoped that another sub-cell with a band gap width of about 1.0 eV can be added between GaAs and Ge to form a four-junction cascade battery. Due to material limitations, the four-junction cascade battery is far below the expected level. Therefore, people turn more attention to other technical approaches to explore the feasibility of five-junction and six-junction cascade batteries. However, the photoelectric conversion efficiency of the five-junction and six-junction integral cascade battery is far lower than the GalnP/Ga(In)As/Ge triple-junction cascade battery. G.Z.Yue et al. prepared a -Si:Hi/nc-Si:H/nc-Si; H triple-junction cascade solar cell using nano-Si thin film (nc-Si:H) as the intrinsic layer. Because such a battery structure effectively combines materials with different band gaps, it improves the spectral response range of the battery, and at the same time reduces the light-induced degradation effect of the battery, so that it has a higher conversion efficiency (13.2%) And lower output power attenuation characteristics.
(8) Increase the conductive path
Adding new conductive paths to reduce shading loss can greatly reduce power conversion loss, and the use of new laser processing technology can improve the photoelectric conversion efficiency of solar cells. The manufacturing process of solar cell electrodes is a very important link in solar cell manufacturing. The quality of the metallization process used in this process determines the shading area and the loss of series resistance. The Buried Gate Solar Cell (BCSC) process developed by the University of New South Wales is one of them. It uses laser or mechanical methods to cut and form trenches on a lightly diffused surface protected by nitride or oxide. These trenches are etched and After cleaning, a special heavy doping is performed again, and then through self-aligned electroplating technology, nickel, copper and a thin layer of silver are plated to achieve metallization. The depth to width ratio of the grooves of this structure can reach 5:1. In this way, compared with the conventional grid-making technology, the shading area is reduced, the resistance of the gate line itself is also reduced, and the low contact resistance between the gate line and the heavily doped trench region can enable the solar cell to obtain a larger fill factor. In addition, the heavy doping of the trench region forms electrode passivation, thereby obtaining a higher sheet resistance, thereby obtaining a higher voltage, and the open circuit voltage of the battery can reach 700mV. Advent Solar uses a launching area wrap technology, which uses a laser to drill through holes in the silicon wafer. The highly doped wall conducts the current on the front surface to the back electrode layer on the back surface, which can further reduce the shielding loss and improve the photoelectricity. Conversion efficiency.
(9) Electrodes prepared by stencil printing
The series resistance of the positive electrode of the stencil printed battery avoids the shortcomings of “peaks” and “valleys” that are easily formed by the fine grid of electrodes printed by ordinary nylon mesh screens, thereby reducing the series resistance. Using special stainless steel mesh, the thin grid part is 100% open, the grid line width is 50um, the screen life can reach 60,000 times, and it can realize the grid line with high uniformity and high aspect ratio; and the common nylon mesh cloth. Compared with the printed electrodes, the series resistance of the stencil printing is reduced by 12%, the effect is obvious, and the conversion efficiency of the solar cell is increased by 0.12%.
(10) Secondary knotting technology
The new process of making N+P type silicon solar cells through secondary constant source diffusion and constant diffusion can alleviate the damage to the silicon surface lattice caused by the diffusion of high-concentration shallow junction phosphorus. Compared with the conventional one-time junction process, due to the reduced range of the dead layer and the increase in the relative spectral response, the short-circuit current I- of the manufactured solar cell is increased by about 0.7%, and the open-circuit voltage U is increased. There is also a significant improvement. The photoelectric conversion efficiency has increased from 17.34% of the battery prepared by the conventional process to 17.7%.
The downstream of the photovoltaic power generation industry chain is the application system link, which mainly improves the total power generation efficiency of the photovoltaic power generation system by improving the effective receiving area of photovoltaic modules and the maximum power point tracking technology.
Through the above article, we have learned the specific ways to improve the efficiency of photovoltaic modules, so do you know what is the principle of improving the efficiency of photovoltaic modules? Please refer to another article on this site.