Doping Strategies for Next Generation CdTe Solar Cells

在过去的6年中，CdTe光伏器件（PV）在经历了前10年的相对停滞之后，获得了稳定的性能改善。这些改进在很大程度上是由一家公司First Solar Inc推动的，该公司已成功地将该技术商业化，成为世界上最大的薄膜光伏制造商。这种稳定的效率增加首先来自于关注增加光子吸收以改善电流收集。虽然改善这些器件中的电流收集已经产生了越来越高的效率，但重要的是解决CdTe器件目前所遭受的电压损失。只有这样，CdTe PV才能充分发挥其潜力。目前，CdTe遭受显著的电压不足，这阻止了器件超过900 mV的开路电压。这种电压缺陷归因于两种现象：a）约1014/cm 3的低掺杂密度和B）低少数载流子寿命（通常小于5 ns）。同时改善两者将导致改善的开路电压。改善CdTe掺杂的策略包括使用V族掺杂剂，如磷，将在本项目中研究，以改善CdTe薄膜的掺杂水平从1014到1016/cm 3，这是高效CIGS太阳能电池的典型特征。除了V族掺杂，硒合金化也将在本项目中进行探索。有越来越多的证据表明，合金化碲化镉硒（形成CdTexSe 1-x）可以显着提高少数载流子寿命的薄膜，而不诉诸于外来的增长方法。

Over the last 6 years, CdTe photovoltaics (PV) have enjoyed a steady performance improvement after remaining relatively stagnant for the previous 10 years. These improvements have largely been pushed by one company, First Solar Inc, who have successfully commercialised the technology to become the largest thin film PV manufacturer in the world. This steady efficiency increase has come about from, in the first instance, focusing on increasing photon absorption to improve current collection. Whilst improving the current collection in these devices has yielded higher and higher efficiencies, it is important to address the voltage loss which CdTe devices currently suffer from. Only then will CdTe PV fully realise its potential. Currently, CdTe suffers from a significant voltage deficit, which prevents devices from exceeding 900mV open circuit voltage. This voltage deficit has been attributed to two phenomena: a) Low doping density of around 1014/cm3and b) low minority carrier lifetime (typically less than 5ns). Simultaneously improving both will lead to improved open circuit voltages. Strategies to improve doping in CdTe include using group V dopants, such as phosphorus, will be investigated in this project to improve doping levels in CdTe thin films from 1014 to 1016/cm3, which are typical in high efficiency CIGS solar cells. In addition to group V doping, selenium alloying will also be explored in this project. There is growing evidence that alloying CdTe with Se (to form CdTexSe1-x) can significantly improve the minority carrier lifetime of the film without resorting to exotic growth methods.