18650 battery 4800mah.Dye-sensitized solar cell technology

　　1 Introduction

　　Among many new energy sources, solar energy has attracted widespread attention due to its abundant reserves, clean and pollution-free advantages, and smaller geographical restrictions. The utilization of solar energy mainly includes three forms: photothermal conversion, photoelectric conversion and photochemical energy conversion. Solar cell is a photoelectric conversion device that converts solar energy into electrical energy. It can directly provide electrical energy for small appliances and can also be connected to the grid to generate electricity, so it has very broad application prospects. Silicon-based solar cells were the first to be developed and are currently the most mature solar cells. After decades of hard work. The efficiency of monocrystalline silicon solar cells has exceeded 25% and plays a pivotal role in aerospace. However, in terms of civilian use, the current price/performance ratio cannot compete with traditional energy sources. Therefore, various types of new solar cells have emerged.

　　Among many new solar cells, dye-sensitized solar cells (DSC) have developed rapidly in recent years. Its research history can be traced back to the 1960s. Tributsch of Germany discovered that dyes adsorbed on semiconductors can generate electric current under certain conditions, laying an important foundation for photoelectrochemistry. In fact, before 1991, most dye-sensitized photoelectric conversion efficiencies were relatively low (<1%). In 1991, a research team led by Professor Michael Gratzel of the Ecole Polytechnique Supérieure de Lausanne in Switzerland introduced nanocrystalline porous films into dye-sensitized solar cells, significantly improving the photoelectric conversion efficiency of such cells. Compared with silicon-based solar cells, dye-sensitized solar cells (DSC) have the characteristics of low cost, simple process and high photoelectric conversion efficiency.

　　2 Structure and working principle of dye-sensitized solar cells

　　2.1 Structure of dye-sensitized solar cells

　　Figure 1 Structure of dye-sensitized solar cell

　　The structure of a typical dye-sensitized solar cell includes nanoporous TiO2 semiconductor film, transparent conductive glass, dye photosensitizer, hole transport medium and counter electrode.

　　The porous nano-TiO2 film is the photoanode of the battery, and its performance is directly related to the efficiency of the solar cell. This kind of film is generally coated on the surface of conductive glass with TiO2 nanocrystalline particles and sintered under high temperature conditions to form a porous electrode.

　　Transparent conductive glass is generally ITO glass or TCO glass, which plays the role of transmitting and collecting electrons.

　　Dye photosensitizers are adsorbed on the surface of porous electrodes and are required to have broad visible spectrum absorption and long-term stability.

　　The hole transport medium mainly plays the role of redox and electron transport. The main difference between various dye-sensitized batteries is also the hole transport medium.

　　The counter electrode generally uses a platinum electrode or a platinum electrode with a single electron layer, which is mainly used to collect electrons.

　　2.2 Working principle of dye-sensitized solar cells

　　The basic working principle of dye-sensitized solar cells is as follows: when the incident light with energy lower than the band gap of the porous nano-TiO2 film but equal to the characteristic absorption wavelength of the dye molecules is irradiated on the porous electrode, the dye molecules adsorbed on the surface of the porous electrode will The electrons are stimulated to jump to the excited state, and then injected into the TiO2 conduction band, and the dye molecules themselves become oxidized. The electrons injected into TiO2 are enriched to the conductive glass substrate through diffusion, and then enter the external circuit. The dye molecules in the oxidized state obtain electrons from the electrolyte solution and are reduced to the ground state. The oxidized electrons in the electrolyte diffuse to the counter electrode, which completes a photoelectrochemical reaction process. In dye-sensitized solar cells, light energy is converted directly into electrical energy, with no net chemical changes occurring inside the cell.

　　The working principle of DSC cells is similar to photosynthesis in nature and is different from traditional silicon cells. Its absorption of light is mainly achieved through dyes, while the separation and transport of charges is controlled by the kinetic reaction rate. The transport of charge in TiO2 is completed by majority carriers, so this kind of battery does not have very strict requirements on material purity and preparation process, which greatly reduces the production cost.

　　3 Advantages of dye-sensitized solar cells

　　3.1 Price and process advantages

　　The light absorption and carrier transport of traditional solar cells are accomplished by the same substance. In order to prevent the recombination of electrons and holes, the materials used must be of high purity and have no structural defects. Therefore, it is very important for semiconductors. The process requirements are very high, making it difficult to reduce costs. The dye-sensitized photoelectrochemical cell only generates carriers on one band, that is, after the anode is photosensitized, electrons are injected into the nano-TiO2 conduction band, while holes remain on the dye on the surface. Therefore, the recombination of charges is limited, so polycrystalline and low-purity materials can be used, the process is simpler, and the cost is greatly reduced. Currently, the price of dye-sensitized solar cells is 1/5 to 1/10 of that of silicon solar cells.

　　3.2 High theoretical photoelectric conversion efficiency

　　Current dye-sensitized solar cells are mainly based on liquid electrolytes, and their theoretical photoelectric conversion rate can be stabilized at more than 10%, which is not inferior to polycrystalline silicon solar cells. All-solid-state cells using solid organic hole transport materials as electrolytes are in Under monochromatic light, it can even reach 33%.

　　3.3 Other advantages

　　Dye-sensitized solar cells have high transparency and can be made into transparent products; prepared on flexible substrates, the cells can be made into various shapes, greatly expanding their application scope; they can be used under various lighting conditions; they are sensitive to light It is not sensitive to the incident angle and can make full use of refracted and reflected light; it has a wide operating temperature and the upper limit can be as high as 70°C.

　　4 Problems and development prospects of dye-sensitized solar cells

　　4.1 Main problems existing in dye-sensitized solar cells at this stage

　　At present, the photoelectric conversion efficiency of dye-sensitized solar cells (area <0.5cm2) has reached 11.04%. However, the photoelectric conversion efficiency of large area and practical significance has always been around 5% (maximum 5.9%), and batteries with an area larger than 100cm2 have not been reported yet. Compared with the conversion efficiency of traditional silicon solar cells, there is still a certain gap, and the photoelectric conversion efficiency of dye-sensitized solar cells still needs to be improved.

　　The most widely used liquid electrolyte dye-sensitized solar cells currently mainly use liquid organic small molecule compound solvents, which have low boiling points, are easily volatile, and have high fluidity, which can cause a series of problems such as electrode corrosion, electrolyte leakage, and short life. It brings difficulties to the sealing and long-term use of the battery.

　　The main challenges facing the development of dye-sensitized solar cells include the following aspects: low-temperature preparation and flexibility of efficient electrodes (photoanode and counter electrode); design and development of cheap and stable full-spectrum dyes; encapsulation and packaging of liquid electrolytes Preparation of efficient solid electrolytes and solutions to related problems, etc.

　　4.2 Development prospects of dye-sensitized solar cells

　　Since liquid electrolyte dye-sensitized solar cells have a series of problems, finding suitable solid-state hole transport materials to replace liquid electrolytes and preparing all-solid-state dye-sensitized solar cells will be an important research direction.

　　Figure 2 Schematic diagram of the structure of all-solid-state sensitized titanium dioxide solar cells

　　All-solid-state sensitized solar cells are mainly composed of a transparent conductive substrate, a dense titanium dioxide layer, a dye-sensitized multi-phase junction and a metal electrode. Among them, the dense titanium dioxide layer is introduced to prevent short circuit caused by direct contact between the conductive substrate and the hole transport material. Dye-sensitized multiphase junctions mainly contain porous titanium dioxide membranes, dyes, hole transport materials and some additives.

　　The working principle of all-solid-state sensitized solar cells is that the electrons of the dye in the multi-phase junction are excited by light with an energy lower than the forbidden band width of titanium dioxide and transition to the excited state, and then injected into the conduction band of titanium dioxide, and the dye molecules themselves transform into oxidation state. The electrons injected into the titanium dioxide are concentrated in the conductive substrate and flow to the metal electrode through the external circuit. The dye molecules in the oxidized state obtain electrons through the hole transport layer (or in other words, the holes in the dye molecules are injected into the hole transport layer, and finally reach the metal electrode and are reduced. Same as the liquid electrolyte dye-sensitized solar cell, in the whole process The various substances in it do not appear to change, but light energy is converted into electrical energy.

　　In addition to all-solid-state sensitized solar cells, the future development direction of dye-sensitized solar cells also includes the following aspects: low-temperature preparation and flexibility of efficient electrodes (photoanode and counter electrode); development of cheap and stable full-spectrum dyes Design and development; packaging of liquid electrolytes, preparation of high-efficiency solid electrolytes and solutions to related problems, etc.

　　5 Summary

　　At present, dye-sensitized solar cells have developed to the stage of transition to industrialization. On the basis of existing technology, further reducing costs, improving efficiency and stability, and promoting the process of industrialization are inevitable development trends. Dye-sensitized solar cells have a huge price advantage over other types of solar cells, although there are still some problems. , but we believe that in the near future, with the further development of technology, this kind of solar cell will have very broad application prospects.

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