Silicon Thin Film Solar Cell Electrode Contact Characteristics

As an unexhausted clean energy, the utility and development of solar energy is paid more attention by people. Crystalline thin films solar cell has more merits: high conversion efficiency of crystal silicon solar cells, long lifetime of bulk silicon solar cells, simple manufacturing processing of a-Si thin films solar cell.Crystalline thin films solar cell consist of several layers of different chemical composition and hence different optical and electronic properties. The structure of solar cell is glass/TCO/pin or nip/TCO/Al or Ag in this text. There are interface effect between different layers, and the properties of solar cell is influenced by them. TCO/p, p/i and n/TCO/Al are important interfaces. We mainly research on the contact characteristic of TCO/p and n/TCO.The experiments include:(1)p-Si:H were deposited on different TCO (SnO₂, ZnO:Al, SnO₂/ZnO:Al) byPECVD, the contact characteristic of different TCO and p-Si:H was studied;(2) ZnO:Al were textured, then the influencing factors on rough surface of ZnO:Al are researched. p-μc-Si:H were deposited on different roughness ZnO:Al by PECVD, then the contact characteristic of different roughness ZnO:Al with p-μc-Si:H were analyzed;(3) n-a-Si:H were deposited on ZnO:Al by PECVD, then ZnO:Al were prepared on n-a-Si:H by electron beam evaporation and magnetron sputtering, then the contact characteristic of n-a-Si:H/ZnO:Al were analyzed.The results as follow:(1) The crystalline condition of p-Si:H on different TCO are analyzed systematically: the crystalline volume fraction of p-Si:H on SnO₂ higher than others. Through analyzing the cause is that the rough surface of SnO₂ has more structures such as surface bulge, groove, bench, etc, and these structures may have effect on the nucleation and grow of films.(2) Then the effect of the parameters on the contact characteristic of TCO/P was studied. In our experiment it was showed that contact characteristics of SnO₂/p-Si:H is not superior to ZnO:Al/p-Si:H and SnO₂/ZnO:Al/p-Si:H.Through analyzing the cause is that: (1) the interface between ZnO:Al/p-Si:H has more interface states; (2) the surface of ZnO: Al is not textured, and the surface of SnO₂ is rough; (3) the carrier concentration of ZnO:Al that we used is bigger than SnO₂, (4) the stability of ZnO: Al against H plasma treatment.(3) ZnO:Al were textured by texture liquid that is mixed with de-ionized and 0.5% diluted HCl., then the influencing factors on rough surface of ZnO:Al are researched: when ZnO: Al films are prepared, the optimum of work pressure must be get, so as to get good optical and electronic properties and rough surface. Meanwhile, only ZnO:Al be prepared at proper temperature range, we can get roughness surface that we need.(4) Based on former research the contact characteristic of different roughness ZnO: Al with p-μc-Si:H were analyzed. It was found that the crystalline volume fraction of p-μe-Si:H on rougher ZnO:Al is higher than the one on smooth ZnO:Al, and their contact resistance are all smaller than on smooth ZnO:Al. So it showed that the roughness is benefit to crystalline of p-μe-Si:H; The crystalline volume fraction of p-μc-Si:H on ZnO: Al of textured time 15s is higher, and their contact resistance is also smaller, so it showed that the textured time has an optimum value; if concentration of B doped is increased shortly (0.1%-0.15%), the change trend is same as the former, and in generally contact characteristic become bad: the crystalline volume fraction of p-μc-Si:H on different roughness ZnO:Al are all decreased, and contact resistance all become bigger. It showed that increasing concentration of B doped is may not benefit to crystalline of p-μc-Si:H, it should has an optimum value.(5) Some research on the contact characteristic of back reflectors: (1) the doping content of the ZnO:Al prepared by electron beam evaporation has an knee point. When the doping content is 2.5%, the contact resistance of n-a-Si:H/ZnO:Al is smallest. Because when the doping content is 2.5%, the resistivity of ZnO:Al is smallest; (2) Keeping the doping content is 2.5%, the contact resistance of n-a-Si:H/ZnO:Al is increasing as the thickness of ZnO:Al is increasing. Through analyzing the cause is that when the thickness of ZnO:Al change a little, the properties (the resistivity and crystallinity) of ZnO:Al is almost same. As the thickness is increasing, the resistance of ZnO:Al is increasing; (3) As to ZnO:Al prepared by magnetron sputtering: the contact resistance of n-a-Si:H/ZnO:Al is decreasing as the thickness of ZnO:Al is increasing. As the thickness of ZnO:Al prepared by magnetron sputtering is increasing, and the crystallinity of ZnO:Al becomes better, the resistivity of ZnO: Al is decreasing.