碱性条件下电化学沉积法制备CdTe半导体薄膜及其性能研究

发布时间：2018-04-11 15:14

本文选题：碱性溶液 + 四甲基氢氧化铵　；参考：《济南大学》2017年硕士论文

【摘要】：CdTe属于II-VI族半导体化合物,具有较窄的禁带宽度(1.45 e V)、较高的光吸收系数和理论转化效率,作为吸收层材料广泛应用于太阳能电池。商业化CdTe太阳能电池组件的转换效率为18.6%,超过多晶硅组件的17.7%。目前制备CdTe薄膜的方法有磁控溅射法、近空间升华法、气相传输沉积法和电化学沉积法等。与其他沉积方法相比,电沉积方法操作简单、成本低廉、容易控制、成膜均匀致密,十分适合于大面积CdTe半导体薄膜材料的制备。目前大多采用酸性溶液进行电沉积,酸性条件下电沉积CdTe薄膜存在着许多问题如:沉积速率低、腐蚀Cd S薄膜、薄膜中Te过量、多孔、界面质量差和结构复杂等。可以通过提高酸性沉积溶液中Te O_2的溶解度提高沉积速率,但是高的沉积速率会增加薄膜中的缺陷,导致器件性能降低。目前关于碱性溶液的电沉积CdTe的报道较少。本论文采用一种新的碱性溶液体系电化学沉积CdTe薄膜,探索薄膜的电化学沉积机理以及工艺参数对薄膜结构与性质的影响。本文的主要研究内容与创新点如下:1、Na OH碱性溶液体系中电沉积CdTe薄膜的研究研究不同p H对Cd~(2+)、Te O_3~(2-)还原电位的影响,p H为9.5时Te O_3~(2-)开始被还原为单质Te的还原电位更正为-0.3 V,Cd~(2+)的还原电位不受p H的影响,为-1.05 V。结合NTA-Na OH-Cd Cl_2-Te O_2电沉积溶液的循环伏安特性,从而确定碲化镉的沉积电位范围在-0.8 V和-1.2 V之间。尝试采用不同的沉积电位沉积CdTe薄膜,发现:刚沉积的CdTe薄膜相组成随着沉积电位的变化而变化。在较正的电位下沉积的薄膜六方相较多,而这种六方相的形成与薄膜中过量的Te有关。经过退火后,六方相转变为立方相,并且薄膜具有好的结晶度和窄的禁带宽度。相组成随薄膜组成的变化而变化,这种变化关系为电化学沉积CdTe薄膜提供了依据。2、TMAH碱性溶液体系中电沉积CdTe薄膜的研究为了中和碱性溶液中的羧基,大量的无机碱Na OH进入溶液,碱金属离子Na~+会掺杂CdTe薄膜进而破坏器件的性能。为了避免Na~+的引入,采用一种不含金属离子的有机强碱四甲基氢氧化铵(TMAH)。整个沉积过程中避免引入其他金属离子,从而减轻对电沉积获得的CdTe多晶薄膜结构的影响。主要研究了沉积温度、光照、沉积电位、NTA/Cd~(2+)络合比对CdTe薄膜组成、结构和性质的影响规律。沉积温度越高,薄膜的沉积速率越快,在-1.0 V、80℃下沉积的薄膜结晶性较好,并沿着(111)取向生长。通过对薄膜表面进行光照,提高了电化学制备CdTe半导体薄膜的沉积速率,还提高了CdTe薄膜的结晶度,-0.8 V光照条件下沉积的薄膜比较符合化学计量比,薄膜相组成随着光照条件的改变而改变。通过调控电沉积溶液中络合剂的含量控制晶体的取向,在NTA浓度较低的条件下,沿着(111)取向择优生长;当溶液中NTA浓度特别高时,以(220)取向为主。
[Abstract]:CdTe belongs to the II-VI semiconductor compound, with narrow band gap (1.45 e V), the absorption coefficient and the theoretical conversion efficiency of higher light absorption layer, as materials are widely used in solar cells. The conversion of CdTe solar energy efficiency business was 18.6%, more than the polycrystalline silicon components 17.7%. the preparation methods of CdTe thin films the magnetron sputtering method, close space sublimation, vapor transport deposition and electrochemical deposition. Compared with other deposition method, electrodeposition method has the advantages of simple operation, low cost, easy control, uniform and compact film materials, is very suitable for large area CdTe semiconductor thin film preparation. Most of the acidic solution electrodeposition of electrodeposited CdTe films under acidic conditions exist many problems such as low deposition rate, corrosion of Cd S films, Te films in excess, porous, complex structure and poor quality of the interface can be provided through. The high solubility of acid deposition solution Te O_2 improved the deposition rate, but the high deposition rate will increase the defects in the film, resulting in reduced device performance. At present, few reports on the electrodeposition of CdTe alkaline solution. This paper adopts a new electrochemical deposition system of alkaline solution of CdTe films, to explore the influence of film by electrochemical deposition the mechanism and process parameters on the structure and properties of the films. The main research contents and innovations are as follows: 1, research on Na OH alkaline solution system of Electrodeposited CdTe films on different P H Cd~ (2+), Te O_3~ (2-) reduction potential effects of P H 9.5 Te O_3~ (2-) began to be reduced to the reduction potential of elemental Te corrections for the -0.3 V Cd~ (2+) reduction potential is not affected by the P H, -1.05 V. NTA-Na OH-Cd Cl_2-Te combined with cyclic voltammetry of O_2 electrodeposition solution, so as to determine the deposition potential of cadmium telluride In the range between -0.8 V and -1.2 V. Try to use the deposition potential deposition of CdTe thin films, different found as deposited CdTe thin films phase composition changes with the deposition potential deposition. In the positive potential of the six party in the film, and the six phase formation in excess of Te and in the film about. After annealing, the six phase transition to the cubic phase, and the film has good crystallinity and narrow band gap. The phase composition changes with the film composition and change the relationship between the change of.2 provides a basis for the electrochemical deposition of CdTe thin films, TMAH alkaline solution of Electrodeposited CdTe films to neutralize alkaline solution a large number of carboxyl groups in inorganic alkali Na OH into the solution of alkali metal ions, Na~+ properties of doped CdTe thin films and thus damage the device. In order to avoid the introduction of Na~+, using a metal ion containing organic alkali tetramethyl hydroxide Ammonium bromide (TMAH). The introduction of other metal ions to avoid the deposition process, thereby reducing the effect on the electrical deposition of CdTe polycrystalline thin film structure are investigated. The deposition temperature, illumination, deposition potential, NTA/Cd~ (2+) complex on CdTe film. The influence of structure and properties of the deposition temperature is higher. The deposition rate, more quickly, in -1.0 V, 80 DEG C thin film crystalline deposition is better, and along the (111) orientation. The light through the surface of the film, improve the deposition rate of CdTe semiconductor thin films prepared by electrochemical method, but also improve the crystallinity of CdTe films, -0.8 V light film under the condition of deposition compared with stoichiometric films, phase composition changes with the change of illumination condition. Control the crystal orientation by regulating the contents of the electro deposition solution of complexing agent, the concentration of NTA in the conditions of low along the (111) preferred orientation growth; When the concentration of NTA in the solution is very high, the (220) orientation is dominant.

【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】：TQ132.44;TB383.2

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