New designs for thin film solar cells

为了到2050年将全球变暖控制在2摄氏度以内，可再生能源发电量必须从15%增加到65%(国际可再生能源协会[1])，所有情景都认为太阳能光伏发电将在其中发挥重要作用：国际能源署(IEA)世界能源展望预测，太阳能发电量将从2017年的430Tw-h增加到2040年的6410Tw-h，在其可持续情景[2]中。太阳能光伏(光伏)做出了巨大贡献，2010年至2017年销售额同比增长24%。这是由领先的太阳能光伏技术--晶片硅的成本暴跌推动的，该技术在远东地区实现了大规模生产扩张。它占据了95%的市场份额。累计装机容量每翻一番，成本就会继续下降约25%(太阳能的摩尔定律)。硅的低成本薄膜竞争对手的优势在于，它们使用高吸收化合物半导体的薄涂层，而不是切片晶片。它们本身就是一项大生意，仅镉镉一项的年营业额估计就达到10亿美元。然而，薄膜技术必须不断提高性价比，才能在硅片生产成本不断下降的情况下保持领先地位。例如，全球最大的薄膜光伏制造商First Solar刚刚将其CdTe模块的尺寸扩大了一倍，并改变了结设计，以保持其作为现有光伏成本最低的市场地位。尽管薄膜光伏在商业上取得了成功，但大型商业参与者相对较少。造成这种情况的原因之一是技术风险，以及生产太阳能电池所需的专有技术。以市场领先者CdTe为例，半导体p-n结的基本设计40年来一直保持不变。然而，它包含了一些无法克服的基本材料弱点。具体地说，CdTe吸收体是p型的，以便使其与n型透明电极兼容。由于基本的材料原因，这限制了可实现的电压，并使真正的欧姆接触变得不可能。在实践中，这两个因素都限制了太阳能电池的能量转换性能。在这个项目中，我们将设计和制造一种新型的薄膜太阳能电池架构，它避免了这些问题，并有可能通过简化的制造方案实现更高的效率性能。我们将使用n型CdTe吸收体，它既不受掺杂限制，也不受p型接触问题的影响。工作方案的重点将是重新设计太阳能电池结构，以适应n型镉镉电池并实现其优势。我们预计，新设计将能够产生1V的开路电压，而目前结构的开路电压为0.87V。这将推动太阳能转换效率高达25%左右。此外，由于设备的处理和联系将不需要依赖‘黑盒’过程和技术诀窍，新的设计将更具生产力，并将为制造商提供一个有吸引力的替代方案。[1]2017https://www.irena.org/publications/2018/Jan/Renewable-power-generation-costs-in-2017[2]国际能源署世界能源展望‘可持续方案’https://www.iea.org/weo2018/中的可再生发电成本

To limit global warming to 2degC by 2050, renewable power generation must increase from 15 to 65% (Int Renewable Energy Association [1]), and all scenarios concur that solar photovoltaic electricity generation will play a large part in this: The International Energy Agency (IEA) World Energy Outlook forecasts that solar electricity production should increase from 430 Tw-h in 2017 to 6,410 Tw-h in 2040 in its 'Sustainable Scenario' [2].Solar PV (photovoltaics) is making a strong contribution, with a 24% year on year increase in sales from 2010 to 2017. This has been driven by the tumbling costs of the leading solar PV technology, wafer silicon, which has seen massive production expansion in the Far East. It accounts for 95% of the market. Costs continue to fall by about 25% for each doubling of cumulative installed capacity ('Moore's law for solar'). Low cost thin film competitors to silicon have the advantage that they use thin coatings of highly absorbing compound semiconductors rather than sliced wafers. They are big business in themselves, with a turnover of an estimated $1,000 million per annum for CdTe alone. Nevertheless, the thin film technologies must continually improve their cost/performance ratio in order to stay ahead of the ever-falling costs of wafer silicon production. For example, the largest thin film PV manufacturer worldwide, First Solar, has just doubled the size of its CdTe modules and changed its junction design in order to maintain its market position as having the lowest cost PV available. Despite the commercial success of thin film PV, there are relatively few large commercial players. One of the reasons for this is the technological risk, and the amount of know-how required to produce the solar cells. In the case of the market leader, CdTe for example, the basic design of the semiconductor p-n junction has remained unchanged for 40 yrs. However, it contains some basic materials weaknesses that cannot be overcome. In particular, the CdTe absorber is p-type so as to make it compatible with the n-type transparent electrode. For fundamental materials reasons this limits the voltage achievable, and it makes true Ohmic contacting impossible. Both of these factors act to limit the energy conversion performance of the solar cells in practice. In this programme we will design and fabricate a new type of thin film solar cell architecture that avoids these issues and has the potential for higher efficiency performance with simplified manufacturing protocols. We will use n-type CdTe absorbers, which do not suffer from either the doping limitations or contacting issues of p-type. The work programme will centre on re-designing the solar cell architecture in order to accommodate the n-type CdTe and to realize its advantages. We expect that the new design will be capable of generating open circuit voltages of 1 V compared to the 0.87 V of present day structures. This will push solar energy conversion efficiencies up to about 25%. Moreover, since the device processing and contacting will not need to rely on 'black box' processes and know how, the new design will be more producible and will present an attractive alternative to manufacturers.[1] Renewable Power Generation Costs in 2017https://www.irena.org/publications/2018/Jan/Renewable-power-generation-costs-in-2017[2] International Energy Agency (IEA) World Energy Outlook 'Sustainable Scenario'https://www.iea.org/weo2018/