Thin-film solar cells have attracted the attention of researchers for their low production cost, light weight, less consumables, and good response to weak light. Thin-film solar cells can be manufactured using cheap ceramics, graphite, metal sheets and other materials as substrates. The thickness of the film that can generate voltage is only a few μm, and the current conversion efficiency can reach up to 13%. Let’s take a look at the principles, advantages and disadvantages of thin-film solar cells with the editor.
Principle of Thin Film Solar Cell
In a chemical battery, the direct conversion of chemical energy into electrical energy is the result of spontaneous chemical reactions such as oxidation and reduction inside the battery, which are carried out on the two electrodes respectively. The negative electrode active material is composed of reducing agents with relatively negative potential and stable in the electrolyte, such as active metals such as zinc, cadmium, and lead, and hydrogen or hydrocarbons. The positive electrode active material is composed of oxidants with positive potential and stable in the electrolyte, such as metal oxides such as manganese dioxide, lead dioxide, nickel oxide, oxygen or air, halogens and their salts, oxyacids and their salts, etc. .
Electrolyte is a material with good ion conductivity, such as acid, alkali, salt aqueous solution, organic or inorganic non-aqueous solution, molten salt or solid electrolyte, etc. When the external circuit is disconnected, although there is a potential difference (open circuit voltage) between the two poles, there is no current, and the chemical energy stored in the battery is not converted into electrical energy. When the external circuit is closed, current flows through the external circuit under the action of the potential difference between the two electrodes.Also read:Why is lithium used in batteries
At the same time, inside the battery, since there are no free electrons in the electrolyte, the transfer of charges must be accompanied by oxidation or reduction reactions at the interface between the two-pole active material and the electrolyte, as well as the material migration of reactants and reaction products. The transfer of charges in the electrolyte is also accomplished by the migration of ions. Therefore, the normal charge transfer and material transfer process inside the battery is a necessary condition to ensure the normal output of electric energy. When charging, the direction of the electricity and mass transfer process inside the battery is just opposite to that of the discharge; the electrode reaction must be reversible to ensure the normal progress of the mass transfer and electricity transfer process in the opposite direction.
Therefore, the reversibility of the electrode reaction is a necessary condition for forming a battery. is the Gibbs reaction free energy increment (Joule); F is the Faraday constant = 96500 library = 26.8 amp hours; n is the equivalent number of the battery reaction. This is the basic thermodynamic relationship between the electromotive force of the battery and the reaction of the battery, and it is also the basic thermodynamic equation for calculating the energy conversion efficiency of the battery. In fact, when the current flows through the electrode, the electrode potential will deviate from the thermodynamic equilibrium electrode potential, this phenomenon is called polarization. The greater the current density (current passing per unit electrode area), the more severe the polarization. Polarization is one of the important causes of battery energy loss. There are three reasons for polarization:
① The polarization caused by the resistance of each part of the battery is called ohmic polarization;
② The polarization caused by the retardation of the charge transfer process in the electrode-electrolyte interface layer is called activation polarization;
③ The polarization caused by the slow mass transfer process in the electrode-electrolyte interface layer is called concentration polarization. The way to reduce the polarization is to increase the electrode reaction area, reduce the current density, increase the reaction temperature and improve the catalytic activity of the electrode surface.
Advantages and disadvantages of thin film solar cells
Due to the use of less materials, thin-film solar cells have a significantly lower cost per module than stacked solar cells, and the energy required for the manufacturing process is also smaller than stacked solar cells. It also has The integrated connection module saves the cost of fixing and internal connection of independent modules.
In the future, thin-film solar cells may replace silicon solar cells commonly used today and become the mainstream of the market. The main difference between amorphous silicon solar cells and monocrystalline silicon solar cells or polycrystalline silicon solar cells is the difference in materials. The materials of monocrystalline silicon solar cells or polycrystalline silicon solar cells are sparse, while the materials of amorphous silicon solar cells are SiH4. Because of the different materials, the structure of amorphous silicon solar cells is slightly different from that of crystalline silicon solar cells.Also read:What is the main mineral in lithium batteries
The biggest advantage of SiH4 is that it has good light-absorbing effect and light-guiding effect, but its electrical properties are similar to insulators, which are far from the semiconductor properties of silicon, so SiH4 was initially considered to be an unsuitable material. But scientists overcame this problem in the 1970s, and soon after, RCA in the US produced the first amorphous silicon solar cells. Although SiH4 has good light-absorbing effect and light-guiding effect, its crystal structure is worse than that of polycrystalline silicon solar cells, so the problem of suspended bonds is more serious than that of polycrystalline silicon solar cells, and the rate of recombination of free electrons and holes is very fast; in addition, the crystal structure of SiH4 Irregularities hinder the movement of electrons and holes and shorten the diffusion range.
Based on the above two factors, when light is irradiated on SiH4 to generate electron-hole pairs, the electrons and holes must be separated as soon as possible to effectively generate the photoelectric effect. Therefore, most amorphous silicon solar cells are made very thin to reduce the recombination of free electrons and holes. Because SiH4 has a good light absorption effect, although the amorphous silicon solar cell is made very thin, it can still absorb most of the light.
The biggest advantage of amorphous silicon solar cells is low cost, while the disadvantages are the low efficiency and the degradation of photoelectric conversion efficiency over time. Therefore, amorphous silicon solar cells are widely used in the small power market, but they are less competitive in the power generation market.