Development of a Soft Process for CdTe Solar Cell using Photo-assisted Electrodeposition

为了开发一种新的CdTe薄膜太阳电池软工艺，研究了氨性碱性电解液中光辅助电沉积CdTe的工艺。用电阻率和霍耳效应测试了电沉积的CdTe多晶层的电学性能。电沉积态的CdTe多晶层为p型，电阻率为10^7-10^9Ω cm，载流子密度为10^9- 10^9 Ω cm<11><-3>，迁移率约为10^10 Ω cm。1 cm ^2 V^<-1>s^<-1>。来自碱性浴的CdTe层的这种高电阻率可能导致低效率的太阳能电池。用透射电子显微镜研究了碱性电解液中电沉积碲化镉层的微观结构，并与传统的酸性硫酸盐电解液进行了比较。从基本电解质作为^-沉积的CdTe层由随机取向的晶粒尺寸为约。10 nm的微晶，而那些从酸性电解质由有缺陷的柱状晶粒与优选的<111>生长方向。每个柱状体的直径约为150 nm。从基本电解质的多晶CdTe沉积物的小晶粒尺寸表明，在电沉积过程中经常发生新的晶粒的成核。通过在Ar气氛中在573 K下退火1 h，来自基本电解质的CdTe晶粒生长约四倍，但同时，在晶界处形成纳米空隙。相比之下，CdTe晶粒从酸性电解质不生长退火相同的条件。由于大的晶粒尺寸对于用于高效率太阳能电池的CdTe层是期望的，因此重要的是通过退火控制电沉积期间新晶粒的成核和CdTe沉积物的晶粒生长。

To develop a new soft process for CdTe thin layer solar cell, photo-assisted electrodeposition of CdTe from ammoniacal basic electrolytes was investigated. The electrical properties of polycrystalline CdTe layers electrodeposited were examined by resistivity and Hall effect measurement, As-deposited CdTe layers were found to be p-type with resistivity of 10^7-10^9Ω cm, carrier density of 10^9-10^<11> cm^<-3>, and mobility ca. 1 cm^2 V^<-1> s^<-1>. This high resistivity of CdTe layer from basic baths probably leads to low-efficiency solar cells. The microstructures of CdTe layers electrodeposited from basic electrolytes were investigated by transmission electron microscopy and compared with those from a conventional acidic sulfate electrolyte. As^- deposited CdTe layers from a basic electrolyte were composed of randomly oriented crystallites with a grain size of ca.10 nm, while those from an acidic electrolyte consisted of defective columnar grains with a <111> preferred growth orientation. Each of the columnar has a diameter of of ca.150 nm. The small grain size of the polycrystalline CdTe deposits from the basic electrolyte suggests that nucleation of new grains occurs frequently during electrodeposition. By annealing at 573 K for 1 h in an Ar atmosphere, CdTe grains from the basic electrolyte grew by about a factor of four, but at the same time, nano-voids were formed at the grain boundaries. In contrast, CdTe grains from the acidic electrolyte did not grow by annealing the same conditions. Since a large grain size is desirable for CdTe layers to be used in high-efficiency solar cells, it is important to control the nucleation of new grains during electrodeposition and the grain growth of CdTe deposits by annealing.