| High-efficiency mono-crystalline silicon solar cell is one of the most popular research-areas in the field of solar cells. There are a large number of unsaturated bonds on the surface of silicon, such as dangling bonds and breaking bonds. Surface passivation can remove the recombination centers, decrease the density of surface states of silicon, and increase the light-electronic efficiency of solar cells. The traditional method of surface passivation is PECVD, which deposits a layer of SiNx film on the surface of silicon. But the thermal oxidation method has a better effect on surface passivation because of the match between the SiO2 film and silicon substrate. Thermal oxidation is to grow a good SiO2 film on the surface of silicon as a passivation film, which could decrease the surface state effective and decrease the recombination loss of the minority carrier on the surface.Thermal oxidation uses dry-oxygen oxidation to grow SiO2 film on the surface of silicon because the one grew by this method is compact and uniform. The effect of passivation is closely related to the quantity of SiO2 film. If the film is defective or populated, it will seriously affect the performance of solar cells. The experiment acquires the proper condition for passivation: the oxidation temperature is 780℃, the flow rate of nitrogen is 10L·min-1, the flow rate of oxygen is 6L·min-1, and the oxidation time is 25 minutes. The oxidation atmosphere used to be pure oxygen, but an innovative thought is proposed to study the oxidation reaction at the atmosphere of nitrogen-oxygen mixture, acquiring a very important result which is that the atmosphere of nitrogen-oxygen mixture is better for passivation. In the above condition, after growing SiO2 film on the surface of silicon, the effective lifetime of minority carrier of crystalline silicon is increased more than 10 seconds, decreasing the recombination velocity of crystalline silicon solar cells.Dual ARC is formed of a passivation film at the bottom and an ARC on the top. On the one hand, the passivation film can decrease the surface recombination velocity of light-induced carriers and increase the minority carrier lifetime. On the other hand, the ARC could increase the absorption of light and the efficiency. Two types of customary dual ARC are introduced, including SiO2/TiO2 and SiO2/SiNx. Firstly, TiO2 film which has a depth of 60 nanometers has a good optical match with SiO2 film grew in the proper oxidation condition, which has the depth of 10 nanometers. Secondly, because SiO2 film could decrease the surface combination velocity as a passivation film, which makes SiO2/SiNx a good short-wave response and long-wave response, the reflection rate and exterior quantum efficiency of SiO2/SiNx are better than SiNx film. Thirdly, the reflection rate of SiO2/TiO2 is worse than SiO2/SiNx, because TiO2 film has a good optical match with SiO2 film. Otherwise, the TiO2 film grew by spraying is not compact and uniform, yielding defective on the surface, causes that the exterior quantum efficiency of SiO2/TiO2 is worse than SiO2/SiNx.The experimental condition, including PH value and concentration of electroplating solution and temperature, are related to the performance of electroplating coating and the contact of nickel coating and silicon. The proper experimental condition is: the PH value is four, the temperature is 50℃, and the concentration of NiSiO4 is 150 g·L-1. The SEM experiment shows that the nickel coating is compact and uniform and has a good contact with silicon.
|
PDF Full Text Request