Microstructural evolution of CdTe-based solar cells during chlorine activation

CdTe 基太阳能电池在氯活化过程中的微观结构演变

基本信息

批准号：
EP/I028781/1
负责人：
Budhika Mendis
金额：
$ 13.01万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI028781%2F1
关键词：
Microstructural evolution CdTe based solar

项目摘要

The solar cell market is currently dominated (>80%) by first generation, wafer silicon-based solar cells. Silicon is a poor absorber of light and consequently relatively large volumes of material are required. A direct band gap semiconductor, such as CdTe, has a much higher efficiency for light absorption, so that thin film solar cells can be fabricated. However, in order for CdTe-based solar cells to challenge wafer silicon, its overall device efficiency must be improved. CdTe solar cells always undergo a chlorine 'activation' treatment, where a thin layer of CdCl2 is deposited on the CdTe surface and annealed at a temperature of 400OC for 20-30 mins. This process increases the device efficiency from ~1-3% to ~10-14%. Despite the 10-fold increase in efficiency the activation process remains poorly understood, due to the difficulty in characterising the microstructure at the appropriate length scales (the dominant mechanism is thought to be passivation of grain boundaries due to chlorine segregation). In this project microstructural changes taking place during chlorine activation are characterised using electron microscopy techniques. The PI has developed a novel, cathodoluminescence based method for determining the recombination velocity of an individual grain boundary in a real device structure. Hence it is now possible to examine the role of grain boundaries on solar cell efficiency for the first time. There have also been important advances in instrumentation over the last few years. In particular, monochromated electron microscopes enable local optical property (e.g. band gap, absorption coefficient) measurement at spatial resolutions of only a few nanometres. During chlorine activation, sulphur inter-diffusion takes place at the p-n junction (i.e. the CdS-CdTe interface), which affects carrier generation during illumination. The monochromated electron microscope at Imperial College London will be used to characterise the effects of sulphur inter-diffusion on optical properties of the p-n junction, and understand how this affects device efficiency.CdCl2 has a low evaporation temperature and is water soluble, making it hazardous to handle on a large scale (e.g. in industrial-scale manufacture). Hence alternative, safer methods for activation, such as the use of chlorine containing gases, will also be explored. The microstructure of solar cells activated using chlorine containing gases will be compared to CdCl2 activated solar cells, and correlated with the measured increase in efficiency. Experimental results will be incorporated into a computer programme for modelling solar cell operation. The purpose of the programme is to identify the dominant mechanism(s) underpinning chlorine activation as well as rapid screening of potential processing routes designed to optimise solar cell efficiency. The latter is a paradigm shift in solar cell fabrication methodology, moving away from methods based on trial and error, which are time consuming and costly.

目前，太阳能电池市场以第一代，基于晶体的硅太阳能电池为主（> 80％）。硅是一种较差的光吸收器，因此需要相对较大的材料。直接带隙半导体（例如CDTE）具有更高的光吸收效率，因此可以制造薄膜太阳能电池。但是，为了使基于CDTE的太阳能电池挑战晶圆硅，必须提高其整体设备效率。 CDTE太阳能电池总是接受氯“激活”处理，其中薄薄的CDCL2层沉积在CDTE表面，并在400oC的温度下退火20-30分钟。此过程将设备效率从〜1-3％提高到〜10-14％。尽管效率提高了10倍，但由于难以表征适当长度尺度的微观结构的困难（认为主要的机制被认为是由于氯隔离引起的晶粒边界的钝化），因此激活过程仍然很少理解。在这个项目中，使用电子显微镜技术来表征氯激活期间发生的显微结构变化。 PI开发了一种新型的基于阴极发光的方法，用于确定实际设备结构中单个晶界的重组速度。因此，现在可以首次检查晶界对太阳能电池效率的作用。在过去的几年中，仪器方面的进步也取得了重要成就。特别是，单色电子显微镜使局部光学特性（例如，带隙，吸收系数）在空间分辨率仅对几种纳米的空间分辨率处进行测量。在氯激活过程中，硫间扩散发生在P-N结（即CDS-CDTE界面），这会影响照明期间载体的产生。伦敦帝国学院的单色电子显微镜将用于表征硫间扩散对P-N交界处光学特性的影响，并了解这如何影响设备的效率。CDCL2的蒸发温度较低，水溶性较低，并且是水溶性的，使其危害大规模处理（例如，在工业制造业中）。因此，还将探索替代性激活的更安全的激活方法，例如使用含有氯气的气体。将使用含氯的气体激活的太阳能电池的微观结构与CDCL2激活的太阳能电池进行比较，并与效率的提高相关。实验结果将纳入用于建模太阳能电池操作的计算机程序中。该程序的目的是确定氯激活的主要机制，以及旨在优化太阳能电池效率的潜在处理途径的快速筛选。后者是太阳能电池制造方法的范式转移，它根据反复试验而远离方法，这是耗时且昂贵的。