A low-cost non-toxic post-growth activation step for CdTe solar cells
A low-cost non-toxic post-growth activation step for CdTe solar cells
复制标题
DOI：
10.1038/nature13435
复制
发表时间：
2014-07-17
期刊：
影响因子：
64.8
通讯作者：
Durose, K.
中科院分区：
文献类型：
--
作者：
Major, J. D.;Treharne, R. E.;Durose, K.
作为市场领先的薄膜太阳能电池技术的基础，碲化镉(CdTe)现在已经站稳了脚跟。随着实验室效率接近20%(1)，镉镉的研究和开发目标是将发电成本进一步降低到每瓦特0.5美元以下。2)并尽量减少对环境的影响。制造过程的核心部分包括用氯化镉掺杂多晶薄膜CdTe。这起到了在CdTe/CDS界面(3，4)形成光伏结并钝化晶界(5)的作用，使得它对于实现高器件效率是必不可少的。然而，尽管自25年前这种工艺路线发展以来，这种掺杂几乎无处不在(6)，但氯化镉有两个严重的缺点：它既昂贵(每克约30美分)，又是有毒镉离子的水溶性来源，在制造过程中对操作员和环境都构成了风险。在这里，我们展示了用氯化镁制备的太阳能电池，它无毒，每克成本不到1美分，具有与处理过氯化镉的对照组相同的效率(约13%)。它们在有源层具有相似的空穴密度(9×10(14)cm(-3))，对氯和氧具有相似的杂质分布，这些元素是重要的p型掺杂。与预期相反，经过氯化镉处理的太阳能电池和经过氯化镁处理的太阳能电池含有相似浓度的镁；这是因为镁从钠钙玻璃基板扩散而来，对器件性能没有不利影响。然而，用其他低成本的氯化物如氯化钠、氯化钾和氯化锰处理会导致引入电活性杂质，这确实会影响器件的性能。我们的结果表明，在现有的制备工艺中，可以简单地用MgCl2直接取代CdCl2，从而既减少了环境风险，又降低了CdTe太阳能电池的生产成本。
Cadmium telluride, CdTe, is now firmly established as the basis for the market-leading thin-film solar-cell technology. With laboratory efficiencies approaching 20 per cent(1), the research and development targets for CdTe are to reduce the cost of power generation further to less than half a US dollar per watt (ref. 2) and to minimize the environmental impact. A central part of the manufacturing process involves doping the polycrystalline thin-film CdTe with CdCl2. This acts to form the photovoltaic junction at the CdTe/CdS interface(3,4) and to passivate the grain boundaries(5), making it essential in achieving high device efficiencies. However, although such doping has been almost ubiquitous since the development of this processing route over 25 years ago(6), CdCl2 has two severe disadvantages; it is both expensive (about 30 cents per gram) and a water-soluble source of toxic cadmium ions, presenting a risk to both operators and the environment during manufacture. Here we demonstrate that solar cells prepared using MgCl2, which is non-toxic and costs less than a cent per gram, have efficiencies (around 13%) identical to those of a CdCl2-processed control group. They have similar hole densities in the active layer (9x10(14)cm(-3)) and comparable impurity profiles for Cl and O, these elements being important p-type dopants for CdTe thin films. Contrary to expectation, CdCl2-processed and MgCl2-processed solar cells contain similar concentrations of Mg; this is because ofMgout-diffusion from the soda-lime glass substrates and is not disadvantageous to device performance. However, treatment with other low-cost chlorides such as NaCl, KCl and MnCl2 leads to the introduction of electrically active impurities that do compromise device performance. Our results demonstrate that CdCl2 may simply be replaced directly with MgCl2 in the existing fabrication process, thus both minimizing the environmental risk and reducing the cost of CdTe solar-cell production.