硅薄膜太阳电池电极接触特性的研究

【作者】 吴芳；

【导师】 王海燕；

【作者基本信息】 郑州大学 ， 凝聚态物理， 2007， 硕士

【摘要】 作为一种取之不尽的清洁能源，太阳能的开发利用正引起人类从未有过的极大关注。晶硅薄膜电池是兼具单晶硅和多晶硅体电池的高转换效率和长寿命以及非晶硅薄膜电池的材料制备工艺相对简化等优点的新一代电池。硅薄膜太阳能电池是由许多不同化学成份的叠层构成的，每一层材料都有不同的光电性能。本论文采用的电池结构是glass/TCO/pin或nip/TCO/Al或Ag背场，电池各层之间存在不同的界面效应，从而影响电池性能。其中TCO/p，p/i及n/TCO/Al是重要的界面。本实验主要研究了TCO/p，n/TCO界面的接触效应。实验内容如下：（1）TCO/p界面：采用等离子体化学气相沉积（PECVD）法在不同的透明导电膜：掺F的SnO₂、掺Al的ZnO（znO：Al），SnO₂/ZnO：Al复合膜上沉积了p-Si：H薄膜，研究了不同的透明导电膜和p-Si：H薄膜之间的接触特性；（2）绒面TCO/p界面：对ZnO：Al薄膜进行腐蚀，研究了其织构的影响因素，接着采用PECVD法在不同织构的ZnO：Al上沉积了p-μc-Si：H薄膜，研究了不同织构ZnO：Al与p-μc-Si：H薄膜的接触特性；（3）n/TCO界面：采用PECVD法在ZnO：Al薄膜上沉积了n-a-Si：H薄膜，接着分别用电子束蒸发和磁控溅射法在n-a-Si：H薄膜上制备ZnO：Al薄膜，研究了n-a-Si：H/ZnO：Al的接触特性。实验结果如下：（1）系统地研究了在不同透明导电膜上沉积的p-Si：H薄膜结晶状况：p-μc-Si：H薄膜在SnO₂上晶化率比较高，分析认为：粗糙衬底表面有更多的表面凸起、沟槽、台阶等结构，而这些结构势必对薄膜成核长大有很大的影响；（2）研究了各项参数对TCO/P接触特性的影响。结果表明ZnO：Al/p-a-Si：H的接触电阻并不比SnO₂/p-a-Si：H高。分析认为：①ZnO：Al/p-a-Si：H接触面上的界面态比较少；②ZnO：Al薄膜表面是未曾织构的表面，SnO₂薄膜表面是具有一定绒度的表面；③本实验采用的ZnO：Al薄膜的载流子浓度较SnO₂薄膜的大；④在H等离子体气氛中，ZnO：Al薄膜比SnO₂薄膜稳定；（3）用去离子水（纯度为p＞8 MΩ·cm）与0.5％的稀盐酸混合成腐蚀液对ZnO：Al薄膜表面进行腐蚀，并研究了其织构的影响因素：在制各薄膜时需要很好的掌握反应气压的最佳点，既保证优良的光电特性又要能腐蚀出一定的绒度。同时，只有在恰当温度范围内制备的ZnO：Al薄膜腐蚀后才会得到适合我们要求的绒面结构；（4）在此基础上又对不同织构ZnO：Al与p-μc-Si：H薄膜的接触特性进行了研究和分析。在织构后的ZnO：Al上沉积的p-μc-Si：H薄膜的晶化率均大于在未织构的ZnO：Al上沉积的p-μc-Si：H薄膜，且它们的接触电阻也均小于未织构的。说明绒面有利于p-μc-Si：H薄膜的晶化；织构时间为15s的ZnO：Al衬底上沉积的p-μc-Si：H薄膜的晶化率较高，且其接触电阻也较低，即织构时间存在最佳点；如略微增大硼掺杂浓度（0.1％～0.15％）的话，其变化规律与轻掺杂的相同，总体来说接触特性变差：在不同织构时间的ZnO：Al衬底上沉积的p-μc-Si：H薄膜的晶化率均下降，且接触电阻均变大；（5）对背电极的接触也作了一些研究：①对于电子束蒸发制备的ZnO：Al薄膜，掺杂浓度存在一拐点，当掺杂浓度为2.5％时n-a-Si：H/ZnO：Al的接触电阻最小，这是因为在掺杂浓度为2.5％时ZnO：Al薄膜的电阻率最小；②保持掺杂浓度为2.5％时，改变ZnO：Al膜的厚度，在厚度变化不大的情况下，n-a-Si：H/ZnO：Al的接触电阻随着ZnO：Al厚度的增加而增大。分析认为，厚度变化不大时，薄膜的性能基本相同（电阻率和结晶度差别不大），但体电阻随着厚度的增加而增加；③磁控溅射制备韵ZnO：Al薄膜，n-a-Si：H/ZnO：Al的接触电阻随着厚度的增加而不断减小，这是因为磁控溅射制备的ZnO：Al薄膜随着厚度的增加，结晶度不断变好，ZnO：Al薄膜的电阻率不断减小。更多还原

【Abstract】 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.更多还原