Principles of thin film solar cells

In a chemical battery, the direct conversion of chemical energy into electrical energy is the result of chemical reactions such as oxidation and reduction occurring spontaneously within the battery, which are carried out on two electrodes respectively. The negative active substance is composed of reducing agents with negative potential and stability in the electrolyte, such as zinc, cadmium, lead and other active metals and hydrogen or hydrocarbons. The positive active substance is composed of oxidants with more positive potential and stability in the electrolyte, such as manganese dioxide, lead dioxide, nickel oxide and other metal oxides, oxygen or air, halogens and their salts, oxic acids and their salts, etc.

Electrolytes are materials with good ionic conductivity, such as acid, base, salt aqueous solution, organic or inorganic non-aqueous solution, molten salt or solid electrolyte. When the external circuit is disconnected, although there is a potential difference (open circuit voltage) between the 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, a current flows through the external circuit under the action of the potential difference between the two electrodes.

At the same time, in the battery, because there is no free electron in the electrolyte, the transfer of charge must be accompanied by the oxidation or reduction reaction between the active substance and the electrolyte interface at the two poles, as well as the material migration of the reactants and reaction products. The transfer of charge 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 electrical energy. When charging, the direction of electric and mass transfer process inside the battery is just opposite to discharge; The electrode reaction must be reversible to ensure the normal process of mass and electricity transfer in the opposite direction.