Solution processed CIGS thin film solar cells from metal chalcogenide precursors

世界的电力需求是惊人的！2014年，地球的电力需求刚刚超过17 TW，随着人口的不断增加，这个数值每年都在增长。很明显，人类面临的最大挑战之一是需要可持续和清洁的能源。太阳光提供了丰富的这一点，近年来，通过在全球制造和安装光电池（PV），人们一直在努力利用这一资源。光伏行业在过去10年中经历了巨大的增长，部分原因是政府以补贴形式提供的支持;然而，这种支持不会永远持续下去。重要的是，一旦补贴消失，世界各地的光伏安装将保持不变，并继续为人们提供清洁电力。虽然大部分装机容量是基于成熟的硅基太阳能电池，但薄膜光伏技术可以节省越来越多的成本，其中使用真空沉积方法沉积的碲化镉（CdTe）和铜铟镓二硒（CIGS）太阳能电池代表了已经成功地从实验室转移到工业的领先材料。然而，降低成本仍然是关键，为了进一步降低成本，重要的是要摆脱昂贵的真空沉积技术，而转向在大气条件下使用溶液化学制备的器件。然而，从溶液中沉积薄膜太阳能电池并不容易。通常，通过将普通金属盐溶解在标准溶剂中来制备溶液，然后将其浇铸到支撑基底上并退火。因此，来自盐的不期望的杂质（例如氯或氧）通常包含在膜内，这对太阳能电池性能是有害的。IBM的研究人员已经成功开发了一种替代方法，即将硫属化物（如硫化铜，硒化铟和硒化镓）溶解在联氨中，并从这种溶液中生产太阳能电池。在这种情况下，使用肼，因为它是唯一已知的在室温下成功溶解硫属化物材料的溶剂。使用这种方法，可以制造CIGS薄膜，而不包含有害杂质，因为所有所需的组成元素都在起始前体中（即铜、铟、镓、硒和硫），没有外来污染物。虽然这种方法已经生产出了迄今为止最高的溶液处理薄膜太阳能电池，但肼是一种剧毒、致癌和爆炸性的溶剂，这使得扩大这种技术非常困难。考虑到这一点，本项目旨在利用硫属化物起始前体的优点制造高效薄膜CIGS太阳能电池（即无有害杂质），同时使用更安全的溶剂组合而不使用肼。拉夫堡的PI最近的工作表明，可以将用于CIGS薄膜生长的硫属化物溶解在结合胺和硫醇源的溶剂中。这些溶剂可以很容易地使用，而不需要复杂的保护设备;它们可以在环境大气中使用（肼需要充满氮气的手套箱）;并且它们不像肼那样受到严格的控制法律（无水肼不能在英国购买）。该项目的目标是使用该技术制造12-14%的CIGS太阳能电池，将低毒性溶剂的优点与肼法中使用的纯起始前体相结合。

The power demand of the world is staggering! In 2014, the power requirements of the earth were just over 17 TW, and with an ever increasing population, this value is growing every year. It is clear then, that one of greatest challenges facing humanity is the need for sustainable and clean sources of power. Sunlight provides this in abundance, and in recent years there has been a drive to utilise this resource, through the manufacture and installation of photovoltaics (PV) worldwide. The PV industry has experienced massive growth in the last 10 years, in part due to governmental support in the form of subsidies; however this support will not last forever. It is important that once subsidies have disappeared, the installation of PV around the world remains constant, and continues to deliver clean power to the population.Whilst the majority of the installed capacity is based on well-established silicon based solar cells, more and more cost savings can be found in thin film PV technologies, where cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) solar cells deposited using vacuum deposition methods represent the leading materials which have successfully moved from lab to industry. However, cost reduction is still key, and to reduce costs further, it is important to move away from expensive methods involving vacuum deposition techniques, and towards devices produced using solution chemistry under atmospheric conditions.However, the deposition of thin film solar cells from solution is not easy. Typically, solutions are prepared by dissolving common metal salts in standard solvents, which are then cast onto a supporting substrate and annealed. As a result, undesired impurities from the salt are often included within the film (such as chlorine or oxygen), which is detrimental to solar cell performance. An alternative approach, which has been successfully developed by researchers at IBM, is to dissolve chalcogenides (such as copper sulphide, indium selenide and gallium selenide) in hydrazine, and produce the solar cell from this solution. In this case, hydrazine has been used as it had been the only known solvent to successfully dissolve chalcogenide materials at room temperature. Using this method, it is possible to fabricate CIGS thin films, without inclusion of detrimental impurities, since all the desired constituent elements are in the starting precursors (namely copper, indium, gallium, selenium and sulphur), with no foreign contaminants. Whilst this method has produced the highest solution processed thin film solar cells to date, hydrazine is a highly toxic, carcinogenic and explosive solvent, which makes up-scaling this technique very difficult.With this in mind, this project aims to fabricate highly efficient thin film CIGS solar cells, using the benefits of chalcogenide starting precursors (i.e. no detrimental impurities), whilst using a safer solvent combination without the use of hydrazine. Recent work by the PI at Loughborough has shown that it is possible to dissolve chalcogenides for use in CIGS thin film growth in a solvent combining an amine and a thiol source. The solvents can be used easily without the need of sophisticated protection equipment; they can be used in ambient atmosphere (hydrazine requires a nitrogen filled glove box); and they do not suffer from strict control laws unlike that of hydrazine (anhydrous hydrazine can not be purchased in the UK). The aim of the project is to fabricate 12-14% CIGS solar cells using the technique, combining the benefits of low toxicity solvents with the pure starting precursors used in the hydrazine method.