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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.

太阳能电池市场目前由第一代硅片太阳能电池主导(80%)。硅对光的吸收能力很差，因此需要相对大量的材料。直接带隙半导体，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。然而，为了让基于CdTe的太阳能电池挑战晶片硅，其整体器件效率必须得到提高。镉镉太阳能电池通常要经过氯活化处理，在镉镉表面沉积一层薄薄的氯化镉，然后在400摄氏度的温度下进行20-30分钟的热处理。该工艺将器件效率从~1-3%提高到~10-14%。尽管效率提高了10倍，但由于很难在适当的长度尺度上表征微观结构(主要机制被认为是由于氯分离导致的晶界钝化)，激活过程仍然鲜为人知。在这个项目中，用电子显微镜技术表征了氯活化过程中发生的微观结构变化。PI开发了一种基于阴极发光的新方法，用于确定实际器件结构中单个晶界的复合速度。因此，现在可以首次研究晶界对太阳能电池效率的影响。在过去的几年里，仪器仪表也取得了重要的进步。特别是，单色电子显微镜能够以仅几纳米的空间分辨率测量局部光学性质(如带隙、吸收系数)。在氯活化过程中，硫在p-n结(即CDS-CdTe界面)发生互扩散，这影响了光照过程中载流子的产生。伦敦帝国理工学院的单色电子显微镜将被用来表征硫的互扩散对p-n结的光学性质的影响，并了解这是如何影响器件效率的。氯化镉的蒸发温度较低，且易溶于水，因此大规模处理(例如在工业规模制造中)是危险的。因此，还将探索其他更安全的激活方法，如使用含氯气体。用含氯气体激活的太阳能电池的微观结构将与氯化镉激活的太阳能电池进行比较，并与测量的效率提高相关。实验结果将被合并到一个计算机程序中，用于模拟太阳能电池的运行。该计划的目的是确定氯活化的主要机制(S)，以及快速筛选旨在优化太阳能电池效率的潜在工艺路线。后者是太阳能电池制造方法的范式转变，摆脱了基于试验和错误的方法，这些方法既耗时又昂贵。