Research On Optimization Of The Surface Antireflection Properties For Multicrystalline Silicon Solar Cells

When the sun light irradiate to the surface of the bare silicon wafer, the loss light exceed 30% because of surface reflection. After cleaning and texturing of the silicon wafer, the surface reflection is still up to about 20%. The processes of the surface texturization of the multicrystalline silicon wafer and the PECVD for multicrystalline silicon solar cells were investigated in this paper. In the process of the surface texturization, for manufacturing optimum surface topography and obtaining the best preparation process to achieve the better antireflection propreties, the effects of the different of the ratio of the etching solution, the temperature and the etching time on surface topography and reflectance were investigated by using various techniques. In the process of the PECVD, the silicon nitride (SiNx) films were deposited on multi-crystalline silicon surface by Plasma Enhanced Chemical Vapor Deposition (PECVD). The effects of the different SiH4/NH3 on the propreties of the monolayer SiNx antireflective films were investigated by using various techniques. The impact of the different thickness on the properties of the double SiNx antireflective coatings prepared by PECVD with different depostion times for the inner and outer films was investigated. The main results of the paper are as follows:(1) Afer the texturing of silicon surface with the acid etching, the surface topography with coorosion pits like "earthworm" were textured on the silicon surface, which is not only conducived to reduce the reflectivity of silicon surface, but also conducive to deposited good quality SiNx film on the silicon surface, to further reduce the surface reflectivity. The best surface morphology were manufactured when the HF:HNO3:H2O=1:5:2, the corrosion temperature is 9℃ and corrosion time is 100s in the corrosion system, which have the evently distributed corrosion pits and the best light trapping effect, achivie the best antireflection effect, the reflection rate was 20%.(2) For the monolayer SiNx films deposited by PECVD with different SiH4/NH3, when the SiH4/NH3 wasl:6, the refractive index of SiNx film was 2.16 and the minimum surface reflectance was 5.9%. For the double SiNx films with different thickness, when the refractive index and the thickness of the inner and outer layer films were 2.36/2.04 and 36nm/50nm, respectively, the best double SiNx films structure was achived. The best reflectance of the SiNx films with the binary complex structure was 5.3% and comparing with the original silicon wafer, the reflectivity was reduced by about 20%, the antireflection effect was best. Furthermore, the SiNx films with the binary complex structure have the better passivation, which can improve the minority carrier lifetime. The multicrystalline silicon solar cells with the best double SiNx films structure have the highest photoelectric conversion effievency, short-ciruit current and open-circuit voltage were 16.83%,8.522mA and 0.626V, respectively.