Research On Key Technologies In Fabrication Of The HIT Solar Cells

HIT (Heterojunction with Intrinsic Thin-layer) solar cells are attracting more and more attention due to the high efficiency and a fairly simple process, which enable them to be the cost-effective alternatives for present c-Si and a-Si solar cells. In this paper, the fabrication technology of the a-Si layers in HIT solar cells, the passivation technology of the a-Si/c-Si interface, and the surface etching of the silicon substrate have been studied in details, in order to obtain high-efficiency HIT solar cells.The a-Si layers of the HIT solar cells were fabricated by PECVD. The optical band gap, deposition rate and conductivity of the amorphous silicon films prepred in different PECVD parameters have been measured and the effect of the parameters on the performance of the solar cells has been studied. The substrate temperature, RF power in the fabrication of the intrinsic a-Si layers were optimized as 200℃and 100W respectively, and the doping concentration (PH3 /SiH4) of the n-type a-Si layer was set as 0.015. The thickness of the intrinsic and n-type a-Si layers were set as 3.5nm and 21.6nm respectively.The passivation of the a-Si/c-Si interface was realized by the pretreatment of the crystalline silicon substrate by diluted hyfluoric acid before the deposition of the a-Si layer. To prevent the over-etching of the hyfluoric acid, we set the pretreating time as 60 seconds, so that the open circuit voltage has been enhanced by 160mV, and the short circuit current has been improved by one magnitude.Textured substrate has been obtained by anisotropic etching using KOH and IPA mixed solution at 80℃while wafer thinning has been realized at the same time. The reflectance of the substrate could be below 11.4% and the thickness of the wafer would be reduced to 250μm, when the etching time was optimized as 50min.