CdTe薄膜的电化学沉积、结构与性能研究

发布时间：2018-07-05 16:22

  本文选题：CdTe薄膜 + 太阳能电池　； 参考：《济南大学》2017年硕士论文

【摘要】：碲化镉(CdTe)薄膜太阳能电池是一种以p型CdTe和n型CdS所组成的异质结为基础的薄膜太阳能电池。CdTe层作为光吸收层,其禁带宽度为1.46 eV,光吸收率高,是一种典型的II-VI族直接带隙半导体。CdTe薄膜太阳能电池具有理论转换效率高,电池性能稳定,制备工艺简单等诸多优点,备受国内外关注。CdTe薄膜的制备方法有很多种,包括近空间升华法,气相输运法,磁控溅射法和电化学沉积法等等。其中,电化学沉积法因其成本低廉,工艺简单,易于大面积制备等优点受到了广大国内外科研人员的青睐。CdS层作为CdTe薄膜太阳能电池的窗口层,CdS中Cl浓度会影响电池中缓冲层的形成,化学浴沉积过程中Cl在CdS薄膜中的引入必将影响电池的性能。Cl掺杂CdTe是形成高效电池的必备条件。在电化学法制备的CdTe薄膜电池中,Cl通常通过电解质溶液在电沉积过程中被引入CdTe薄膜中,以提高薄膜质量和电池性能,但其作用机理尚不清晰。目前电化学沉积的CdTe薄膜的主要问题是晶粒小,晶界多,已有的退火方式会造成薄膜中气孔较多,电池的光生载流子复合严重,电池转换效率低。因此,需要优化电化学沉积CdTe薄膜的退火工艺来提高CdTe薄膜的结构和电池性能。同时,电化学沉积的CdTe薄膜的晶体结构和厚度的特殊性,也需要与其相适应的背接触层沉积和退火条件以提高电池性能。本文重点就以上这些问题展开研究,主要研究内容如下:(1)研究了CdS薄膜中Cl残留对薄膜结构性能及组装电池性能的影响。研究采用醋酸镉与氯化镉两种溶液体系化学浴沉积CdS薄膜。研究发现,两种体系中沉积的CdS薄膜均为六方相结构的n型半导体。退火后,CdCl2体系中制备的CdS薄膜晶粒尺寸要大于Cd(CH3COO)2体系中制备的CdS,其表面平整致密。所有CdS薄膜热处理后的禁带宽度都有所降低,但相比而言CdCl2体系中制备的CdS薄膜的禁带宽度更大。从Mott-Schottky曲线计算的载流子浓度发现,退火会降低CdS薄膜的载流子浓度,但随着更多Cl的引入载流子浓度又会增加。结果表明,CdS薄膜中Cl的残留将导致S空位及膜内应力的减少。通过组装的电池性能发现,采用CdCl2体系制备的CdS薄膜组装的电池性能更优。(2)通过对比含Cl与否的电解质溶液所沉积CdTe薄膜的结构性能,研究了Cl在电解质溶液中的引入对CdTe薄膜的电沉积过程,结构性能及所组装电池性能的影响。研究发现,含Cl电解质溶液中沉积出的CdTe薄膜的结构性能均优于不含Cl电解质溶液中沉积出的薄膜,这要归因于薄膜电导率的提高,进而减少了薄膜沉积过程中反应界面处的电位降,使得薄膜沉积以生长为主,从而获得了优异的初始结晶质量。此外,在不含Cl的电解质溶液中,提高沉积电位同样可获得良好的结晶质量。退火后,含Cl溶液中沉积的CdTe薄膜膜内Cl的残留使得所组装电池的性能得到了提高。(3)提出了一种针对电化学沉积法制备CdTe薄膜太阳能电池的新型退火工艺。与传统退火工艺相比,在Cl激活处理前,一个额外的预退火工艺被引入使得在Cl激活处理前CdTe薄膜可以获得良好的结晶性,最小化晶界的存在。因此,在第二步的Cl激活处理中,适度抑制了Cl沿着晶界渗入CdTe薄膜,并因此获得了较传统一步法更优良的CdS/CdTe界面。界面处孔洞的减少,也使得所组装的电池获得了更高的量子效率及光电转换效率。两步法退火工艺为进一步提高电化学沉积法制备CdTe薄膜太阳能电池的性能提供了一个新的思路。(4)为了优化电化学沉积法制备CdTe薄膜太阳能电池中背接触层的制备工艺,对不同酸腐时间,Cu层厚度及退火温度处理下的电池性能进行了分析,发现当酸腐时间为10 s,Cu层厚度为8 nm,退火温度为200℃的时候,所获电池性能最佳。这是由于对CdTe层进行适时的蚀刻处理可以去除表面的高阻氧化层,并形成一层富Te层。在富Te层表面,制备一层合适厚度的Cu层,经适宜温度退火后生成一个CuxTe层,形成重掺杂层,降低背接触势垒,促进了CdTe与背电极之间形成了欧姆接触,从而最终提高了电池的性能。
[Abstract]:Cadmium telluride (CdTe) thin film solar cell is a kind of thin film solar cell.CdTe layer based on P type CdTe and N CdS as the optical absorption layer. The band gap is 1.46 eV, and the optical absorption rate is high. It is a typical II-VI family direct band gap semiconductor.CdTe thin film solar cell with high theoretical conversion efficiency and battery property. It has many advantages, such as stability, simple preparation technology and so on. There are many kinds of preparation methods concerned with.CdTe films at home and abroad, including near space sublimation, gas phase transport, magnetron sputtering and electrochemical deposition, etc., in which the electrochemical deposition has many advantages, such as low cost, simple process and easy to make large area. The researchers favor the.CdS layer as the window layer of the CdTe thin film solar cell, and the Cl concentration in CdS will affect the formation of the buffer layer in the battery. The introduction of Cl in the CdS film during the chemical bath deposition will certainly affect the performance of the battery and the.Cl doping CdTe is a necessary condition for the formation of high efficiency batteries. In the CdTe thin film battery prepared by the electrochemical method, Cl passes. The electrolyte solution is often introduced into the CdTe film in the electrodeposition process to improve the film quality and battery performance, but its mechanism is not clear. The main problem of the electrochemical deposition of CdTe film is that the grain size is small and the grain boundary is large. The existing annealing methods will cause more pores in the film, and the battery's optical carrier recombination is serious. The efficiency of battery conversion is low. Therefore, it is necessary to optimize the annealing process of Electrodeposited CdTe films to improve the structure and battery performance of the CdTe thin films. At the same time, the crystal structure and thickness of the electrodeposited CdTe films also need to be deposited and retreated to improve the battery performance. The main research contents are as follows: (1) the effects of Cl residue on the structural properties and the performance of the assembled battery in CdS films are studied. The study of the deposition of CdS films by two solution system chemical bath with cadmium acetate and cadmium chloride shows that the CdS films deposited in the two systems are all N type semiconductors with the structure of six square phase. After annealing, the grain size of the CdS film prepared in the CdCl2 system is larger than the CdS produced in the Cd (CH3COO) 2 system. Its surface is smooth and compact. The band gap of all CdS films is reduced after heat treatment, but the forbidden band width of the CdS film prepared in the CdCl2 system is larger. The carrier concentration calculated from the Mott-Schottky curve is found, Annealing will reduce the carrier concentration of the CdS film, but as more Cl is introduced, the carrier concentration will increase. The results show that the residual Cl in the CdS film will lead to the decrease of the S vacancy and the internal stress in the membrane. The battery performance of the CdCl2 system is better to be assembled by the assembly of the battery. (2) whether the Cl is compared or not by comparison. The structure properties of CdTe films deposited by electrolyte solution were studied. The effects of the introduction of Cl in electrolyte solution on the electrodeposition, structural properties and the performance of the assembled cells were studied. It was found that the structure properties of the CdTe films deposited in the Cl electrolyte solution were better than those in the Cl electrolyte solution without the electrolyte solution. This is attributable to the increase of the conductivity of the film, thus reducing the potential drop at the reaction interface during the deposition of the film, making the deposition of the film dominated by growth, thus obtaining excellent initial crystallization quality. In addition, a good crystalline quality can be obtained by increasing the deposition potential in an electrolyte solution without Cl. After annealing, the solution contains a Cl solution. The residue of Cl in the deposited CdTe film film improves the performance of the assembled cells. (3) a new annealing process is proposed for the preparation of CdTe thin film solar cells by electrochemical deposition. Compared with the traditional annealing process, an additional pre annealing process is introduced before the Cl activation process to make CdTe before the Cl activation process. The thin film can obtain good crystallinity and minimize the existence of grain boundaries. Therefore, in the second step Cl activation treatment, Cl appropriately inhibits the infiltration of the CdTe film along the grain boundary, and thus obtains a better CdS/CdTe interface than the uniform gait. The decrease of the pores at the interface also makes the assembled cells obtain higher quantum efficiency and light. The two step annealing process provides a new idea to further improve the performance of CdTe thin film solar cells by electrochemical deposition. (4) in order to optimize the preparation process of the back contact layer in the CdTe thin film solar cell by electrochemical deposition, the electric power of different acid decay time, Cu layer thickness and annealing temperature treatment The performance of the pool is analyzed. It is found that when the acid time is 10 s, the thickness of the Cu layer is 8 nm and the annealing temperature is 200 c, the performance of the battery is the best. This is because the etching treatment of the CdTe layer can remove the high resistance oxidation layer on the surface and form a layer of rich Te layer. The suitable thickness of the Cu layer on the surface of the rich Te layer is suitable. After temperature annealing, a CuxTe layer is generated to form a heavy doped layer, which reduces the potential barrier of the back contact, and promotes the formation of ohm contact between the CdTe and the back electrode, thus ultimately improving the performance of the battery.
【学位授予单位】：济南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2;TM914.4

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