Preparation Of Polycrystalline Silicon Thick-Film And Rapid Thermal Diffusion Of Phosphorus And Boron

Energy crisis has become one of the highly focused issues in the world,and it is global task to seek clean,abundant,and sustainable alternate sources of energy.Photovoltaic(PV)technology is particularly attractive among them,whose key components are solar cells.For traditional silicon solar cells,the silicon material consumption and energy consumption during the long high temperature diffusion process are large,which is hard to reducing costs.Therefore,two solutions are proposed in this paper,which are the preparation of polycrystalline silicon thick-film solar cells based on graphite substrate and the rapid thermal diffusion(RTD)of phosphorus and boron.Because silicon is a kind of indirect bandgap semiconductor material,the polycrystalline silicon thick-film solar cells are prepared to absorb more incident light,which can effectively reduce the amount of silicon material,reduce material costs,and with a wide selection of substrate materials.In order to reduce the diffusion time and energy consumption,the RTD of phosphorus and boron is proposed in this paper.Compared to the traditional diffusion method,the same diffusion effect can be achieved in tens of seconds by RTD.So the costs are significantly reduced.To prepare a polycrystalline silicon thick-film based on graphite substrate,an amorphous silicon layer was first deposited by magnetron sputtering method,and the amorphous silicon layer was crystallized by rapid thermal processing(RTP),then a polycrystalline silicon thick-film was grown by chemical vapor deposition method(CVD).In this paper,the influence of the seed layer and the Zn O buffer layer on the quality of polycrystalline silicon thick-film was investigated.Because the influence of grain boundary on diffusion is obvious and there is not enough research on phosphorus and boron RTD,the diffusion of phosphorus and boron in monocrystalline silicon by RTD was studied.The diffusion coefficient and diffusion activation energy were investigated,for further phosphorus and boron diffusion in polycrystalline silicon thickfilm by RTD.The main achievements in this paper are as follows:(1)SEM images and XRD characterization showed that there was no obvious preferential orientation in the polycrystalline silicon thick-film prepared on the graphite substrate without the seed layer,and the thick-film was easily peeled off from the graphite substrate;the introduction of the seed layer was beneficial to the polycrystalline silicon thick-film and makes it difficult to separate from the substrate.It was found that the seed layer and the upper polycrystalline silicon thick-film demonstrated Si(220)preferential orientation by XRD characterization,and the RTP had a significant effect on the preferred orientation based on the classical nucleation theory and energy minimum principle analysis.(2)By SEM,It was found that the quality of the polycrystalline silicon seed layer was improved by the introduction of the Zn O buffer layer,and the quality of the thick-film was also improved.The XRD results showed that the thick-film was preferentially oriented to Si(400).Through atomic arrangement analysis,it was considered that the atomic arrangement of Zn O buffer layer has a significant effect on the preferred orientation of polycrystalline silicon thickfilm.(3)The phosphorous and boron RTD samples were treated by the angle lapping and staining technique and then observed by metallographic microscope.It was found that the diffusion results were significantly enhanced by increasing the diffusion temperature or time.The optimum phosphorous RTD conditions for making p-n junction were as follows: 850? 30 s,850? 40 s,900 ? 10 s,900 ? 20 s,950 ? 10 s.The RTD diffusion coefficient and diffusion activation energy were calculated and compared with that by the traditional diffusion method,and it was found that the RTD efficiency increased by three orders of magnitude.Through analysis,the high diffusion efficiency was due to the photon-enhanced built-in electric field generated during heating process,which could promote impurities drifting to the area of low concentration and improve the diffusion efficiency.The p-n junctions prepared under the best phosphorous diffusion conditions were tested by I-V.The results showed that the best samples were obtained at 900? for 20 s,with FF of 0.539,JSC of 62.874 m A/cm2,VOC of 498.073 mV and P_m of 8.436 mW.