【作者】 岳红云；

【导师】 李廷举； 吴爱民；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2011， 博士

【摘要】 能源危机和环境污染问题促进了太阳能光伏产业的快速发展,而降低成本、提高光电转化效率则是加快太阳能电池推广应用的重要手段。微晶硅薄膜因其低成本、高效率、无衰减等优点已经成为最有潜力的光伏材料之一。而以柔性材料为衬底的柔性微晶硅薄膜太阳能电池不仅可以实现卷轴式大规模生产,进一步降低成本,还具有可卷曲性和重量轻的特点,使其携带方便、应用更加广泛。但是,其仍存在吸收系数低、界面不稳定、结构均匀性不好等问题,这在一定程度上限制了柔性微晶硅薄膜太阳能电池的发展和应用,本文针对以上主要问题开展了研究。通过调节工艺参数、开发新材料和新方法来达到优化柔性薄膜太阳能电池的陷光结构、解决铝硅界面问题、改善硅薄膜质量等目的。首先,进行了聚酰亚胺(PI)衬底上制备具有织构表面铝背电极的研究,分析讨论了薄膜生长和表面织构形成的机理；其次,将铝镍合金用作柔性硅基薄膜太阳能电池的阻挡层,对铝电极和硅薄膜之间的互扩散有良好的阻挡效果,并对其阻挡机理进行了分析；再次,采用新的两步生长法有效改善了微晶硅薄膜的结构均匀性问题；最后,确定了透明氧化锌铝薄膜(ZnO:Al)的最佳沉积条件,分析讨论了薄膜结构变化的原因及其对性能的影响规律。上述研究为解决柔性微晶硅薄膜太阳能电池中存在的问题和提高电池的性能,提供了丰富的实验和理论基础。论文主要结论如下：1.绒面铝电极的制备及机理研究利用射频磁控溅射技术,室温条件下通过控制工艺参数,在PI柔性衬底上制备了具有表面织构的铝电极。高功率(300-450W)下制备的薄膜沉积速率高、电阻率较低同时具有较高的漫反射率,薄膜的平均漫反射率高达70%。随着工作气压的增加,薄膜的沉积速率降低,表面粗糙度减小,在工作气压为0.5Pa时,薄膜具有较低的电阻率和较高的漫反射率。分析表明：高的沉积功率、低的工作气压和斜向入射的沉积方式都可以提高粒子在薄膜生长表面的动能和迁移率,有利于粒子的聚集及表面岛的长大。而薄膜表面的柱状生长形貌则主要与粒子斜向入射和在沉积过程中的应变能释放有关。这种表面织构的制备方法工艺简单实用,同时还避免了高温对塑料柔性衬底的影响,具有较高的实用价值。2. AlxNiy薄膜制备及阻挡效果分析采用射频磁控双靶共溅射法制备了AlxNiy系列合金薄膜,通过调节靶的功率可以有效调控合金的比例,制备的合金薄膜成分也比较均一。Al、Ni比例为1：1和2：3的薄膜均为多晶结构,对Al、Si互扩散具有较好的阻挡效果,这与其属于置换固溶体,有较高的熔点、较低的自扩散系数有关。其中,AlNi合金对电极电阻的影响最小,与n-Si接触后形成的接触势垒更低,更有利于电子的传输。因此,AlNi合金更适合用来做阻止Al、Si互扩散的阻挡层材料。3.微晶硅薄膜制备工艺优化结合微波电子回旋共振等离子体增强化学气相沉积(ECR-PECVD)技术的特点,提出生长-刻蚀-再生长的两步生长法制备微晶硅薄膜。该方法也可以被称为籽晶层法,即：先生长厚度约为15nm的薄膜,用氢等离子体处理2min得到籽晶层后,继续生长得到微晶硅薄膜。该两步生长法有效消除了非晶孵化层,改善了微晶硅薄膜的纵向均匀性,使薄膜的晶化率从常规生长的24.3提高到了50.7%。结合实验结果,对氢等离子体诱导非晶硅晶化的机理进行了阐述,并提出了两步生长法制备微晶硅薄膜的生长模型。4. ZnO:Al薄膜的制备及结构变化分析采用射频磁控溅射技术以ZnO(含2wt.%Al203)陶瓷靶为溅射靶材制备了高c轴择优取向的ZnO:Al薄膜,并分析讨论了薄膜结构变化的原因及其对薄膜电性能的影响规律。实验结果表明：当溅射功率为100W、工作气压为0.3Pa、衬底温度为250℃时沉积得到的ZnO:Al薄膜有最佳的综合性能,可见光区的平均透过率在90%左右,薄膜电阻率约为3.1×10-3Ω.cm。利用GID-XRD和HRTEM对ZnO:Al薄膜的结构进行了深入研究,结果表明：ZnO:Al的晶格相对于未掺杂的氧化锌不仅在垂直于衬底方向变大,在其它方向上晶格也变大,这说明晶格常数变大除受薄膜应力影响外,还和掺杂本身有直接关系。掺杂量为2%时,除了替位掺杂外还有一部分铝和锌以填隙形式存在,从而使晶格在多个方向变大。通过理论计算证实了上述观点的正确性。更多还原

【Abstract】 Energy supply problem and ecological consideration have taken over as main driving forces in promoting alternative energy sources, in particular, PV solar energy. The cost reduction and efficiency improvement are very essential to push the application of solar cell. Hydrogenated microcrystalline silicon (μc-Si:H) has been confirmed as a promising PV absorber material, owing to its low cost, high convension efficiency and good stablility. Flexibleμc-Si:H thin film solar cell (FMTFSC) can be manufactured in large scale through roll-to-roll process with low cost, and it is more convenient and widely used. However, there are still some disadvantages such as low absorption coefficient, interface interdiffusion, bad structural homogeneity, which restrict the developement and application of FMTFSC to some extent. The scope of this paper is to solve the problems mentioned above.Firstly, the study on the preparation of Al back electrode with texture surface was carried out on PI substrate. The mechanism of the formation of texture surface was discussed. Secondly, the AINi alloy was firstly used as the barrier layer in FMTFSC and the results showed that it had a good barrier effect on the interdiffusion of Al and Si film. Thirdly, a new two-step method was proposed, which can effectively improve the uniformity ofμc-Si:H thin film. At last, the optimism deposition parameters of tramsparent ZnO:Al were obtained and the variation mechanism of film structure and the influence of this variation on the properties were discussed. These studies provide abundant experimental and theoritical fundations to the solution of those problems in FMTFSC. The results of this paper are showed below:1. Study on the growth of texture surface of Al electrode and its mechanismAl electrode with texure suface was prepared at room temperature by r. f sputtering. The film deposited under high power (300-450W) had high depositon rate, low resistivity and high diffuse reflectivity. The average diffuse reflectivity of the film can be as high as 70%. The effect of deposition parameters on the shape and size of three-dimensional surface islands was discussed. High deposition rate, low working pressure and oblique incident can promote the particle kinetic energy and mobility on the film surface, which is favorable for the aggregation and growing up of surface islands. The columnar morphology of the surface is mostly ralated to the oblique incident and the release of strain energy during depositon. It is easy to prepare texture surface with this method and avoids the influence of high temperatur on plastic substrate, which illustrates a good prospect of application. 2. Study on the AlxNiy alloys as the diffusion barriers between Al and SiAlxNiy thin films were prepared using r. f. magnetron co-sputtering technology. The chemical compositions of the films were controlled through adjusting the sputtering powers on Al and Ni targets. When the ratio of Al and Ni were 1:1 and 2:3, the structures of films were polycrystalline. Compared to Ni, AlxNiy alloys had the merits of good oxidation resistance and chemical stability. Among them, the AlNi film had the minimum sheet resistance, the best barrier performance to the interdiffusion between Al and Si, and the lowest contact potential with Si film. Thus, the AlNi film was more suitable in using as the barrier layer of flexible Si based thin film solar cells.3. Study on the uniformity ofμc-Si:H thin filmsBase on the ECR-PECVD technology, a new two-step growth method was proposed to deposite theμc-Si:H thin film without incubation layer. A very thin film in thickness of～15 nm was firstly deposited using ECR-PECVD and then it was treated with H2 plasma to get the seed layer, after that, normal parameters were used to depositμc-Si:H film on it. The uniformity in the longitudinal direction of theμc-Si:H thin film can be improved using this new two-step growth method, and the crystalline volume fraction of the films would be increased from 24.3% to 50.7%.. The mechanism of hydrogen-induced crystallization of amorphous silicon was discribed according to experimental results. And the growth model of the two-step growth method was proposed in this work.4. Preparation and structure analysis of ZnO:Al thin filmsAl-doped ZnO (ZnO:Al) thin films with high c-axis preferred grain orientation were deposited by radio frequency magnetron sputtering. The variation of structure were discussed, and were correlated to the electical properties of ZnO:Al films. The film, deposited at sputtering power of 100 W, working pressure of 0.3 Pa and substrate temperature of 250℃performs high crystalline quality and good properties. The film exhibits a transmittance of about 90% in the visible region and a resistivity of 3.1×10-3Ω·cm. The further studies on structure were performed through GID-XRD and HRTEM. The results show that the interplanar spacings are enlarged in other directions besides the direction perpendicular to the substrate, Apart from the film stress, the doping concentration and the doping site of Al play an important role in the variation of lattice parameters. When the doping content of Al is 2 wt. %, the redundant Al atoms are incorporated into the interstitial position, which leads to the increase of crystal lattice. This viewpoint is also proved by first-principle calculations.更多还原