Addressing Unresolved Scientific Challenges for CdTe-based Solar Cells

太阳能是唯一有能力提供碳中和能源的可再生资源，其数量足以取代目前由化石燃料产生的电力。基于碲化镉（CdTe）的光伏发电在商业相关技术中成本最低，电池和组件效率分别为22.1%和18.6%。为了加快在市场上的进一步部署，需要提高效率和稳定性。该项目解决了进一步将性能提高到理论极限（~33%）所需的基础研究问题。该项目将着眼于改进材料成分，以提高设备的功率转换效率，同时保持长使用寿命的耐久性和稳定性。这个项目将培养一名博士研究生和几名本科生学习先进技术。通过参与国家可再生能源实验室（NREL）和劳伦斯伯克利国家实验室（LBNL）分子铸造厂提供的合作项目，他们的研究经验将得到拓展和丰富。该团队还将利用太阳能研究参与到丹佛公立学校系统的K-12学生中，以激励下一代科学家和工程师。该项目的关键创新是开发具有传统二元层无法获得的新属性的三元合金。这些合金将集成在整个器件结构中，以提高这些器件的效率和稳定性。该项目解决了CdTe面临的三个科学挑战：(i)更换cd以改善现有的收集；（ii）外源掺杂CdTe以提高开路电压；（三）开发无铜背触点，提高稳定性。为了改善电流收集，PI将系统地探索氧化镁锌（MZO）合金作为缓冲层，重点是为该应用定制其导带边缘和电导率。进一步提高开路电压需要增加载流子浓度。多晶CdTe的外部掺杂将涉及到掺杂源材料的生成和稀三元合金的使用，以促进掺杂剂的掺入。最后，PI将利用研究小组对当前基于znte的背触点的理解，设计和实现不使用铜的有效触点，以提高稳定性。所有这些研究都将通过分析技术进行，包括原位XRD，空间和光谱分辨载流子寿命的测量，以及使用扫描TEM和原子探针断层扫描的纳米级结构和组成表征。这些研究将有助于建立这些未开发的II-VI三元合金的工艺-结构-性能关系。

Solar energy is the only renewable resource with the capacity to deliver carbon neutral energy in the quantities required to supplant the power currently generated by fossil fuels. Cadmium telluride (CdTe)-based photovoltaics have the lowest cost of the commercially relevant technologies, with champion cell and module efficiencies of 22.1% and 18.6%, respectively. Improvements in efficiency and stability are required to accelerate further deployment in the marketplace. The project addresses fundamental research questions required to further elevate performance towards theoretical limits (~33%). The project will look at improved material compositions to increase the power conversion efficiency of the device while retaining durability and stability for long operational life. This program will educate a PhD graduate student and several undergraduates in advanced technology. Their research experiences will be broadened and enriched by participation in collaborative programs offered by the National Renewable Energy Laboratory (NREL) and the Molecular Foundry at Lawrence Berkeley National Laboratory (LBNL). The team will also use the solar research to engage in outreach to K-12 students in the Denver public school system to inspire the next generation of scientists and engineers.The key innovation of this project is to develop ternary alloys with novel attributes that cannot be obtained using conventional binary layers. These alloys will be integrated throughout the device structure to improve both the efficiency and the stability of these devices. This project addresses three scientific challenges facing CdTe: (i) replacement of CdS to improve current collection; (ii) extrinsic doping of CdTe to improve open circuit voltage; and (iii) development of copper-free back contacts to improve stability. To improve current collection, the PI will systematically explore magnesium zinc oxide (MZO) alloys as buffer layers, focusing on tailoring its conduction band edge and conductivity for this application. Further improvements in open circuit voltage require increasing carrier concentration. Extrinsic doping of polycrystalline CdTe will involve generation of doped source materials and the use of dilute ternary alloys to facilitate dopant incorporation. Finally, the PI will leverage the research group's understanding of current ZnTe-based back contacts to design and implement effective contacts that do not employ copper for enhanced stability. All of these studies will be informed by analysis techniques including in situ XRD, spatially- and spectrally-resolved measurements of carrier lifetime, and nanoscale characterization of structure and composition using scanning TEM and atom probe tomography. These studies will help establish the process-structure-property relationships for these under-explored II-VI ternary alloys.