Heavy-Atom-Free Sensitizers for NIR-to-Visible Solar Photon Upconversion

非技术性描述高效、廉价地收集太阳能是生产清洁、可持续能源的巨大挑战。太阳发出的光的光谱范围很广，从远红外线到紫外线。然而，只有一小部分这种光可以被太阳能电池中的活性层吸收。如果人们可以扩大太阳能电池板可以捕获的太阳光的光谱范围，那么产生的总功率就会增加。一种增加光吸收率的策略是将两个低能光子联合收割机并将它们的能量融合成一个高能光子，这个过程称为上转换。然后，上转换的光子可以被吸收并用于从否则将被浪费的光中发电。该项目的目标是识别和设计可用于更高效太阳能电池的上转换的新分子。研究人员将联合收割机合成化学和光学表征与理论和机器学习相结合，以实现这一目标。 除了其科学和技术的影响，参与者将从事本地和区域社区大学的学生与真实和持续接触到原始的研究经验。该团队正在追求的一个具体途径是试图将光子上转换研究概念融入当地社区学院的基于课程的学术实验室实验中。这种让社区学院学生接触原创研究的方法旨在帮助克服地理限制，这些限制可能会阻碍这些学生参加更传统的本科生（REU）项目的研究经验，这些项目需要学生长途跋涉到研究地点。一种用于部署光子上转换以提高太阳能光电转换效率的有前景的策略是三重态-三重态湮灭上转换，因为它可以在来自太阳光子的低强度、非相干照射下发生。从历史上看，已经探索用于光子上转换的材料包括基于贵金属络合物、芳基卤化物和量子点的敏化剂。第一类由于金属的高成本而在经济上不可行，第二类在照射下不稳定，并且第三类遭受敏化剂对上转换光的寄生吸收。鉴于这些材料的限制，PI的小组确定了基于硫代方酸菁材料的无重原子上转换敏化剂，他们将其作为实现太阳能光伏应用的NIR到可见光光子上转换的潜在候选者。目标是澄清难以捉摸的结构-功能关系，这些关系历来使识别一般的近红外吸收三重态光敏剂变得具有挑战性，更具体地说，迄今为止，在不使用昂贵的贵金属中心或容易光降解的芳基卤的情况下，难以实现近红外-可见光光子UC，这两者对于太阳能应用都没有吸引力。这项工作的一个关键目标是解决具体的问题，如“什么分子描述符是最规范的同时实现近红外吸收和高系统间交叉产率？”该团队结合了基于超快泵浦-探测光谱、从头算预测和强化学习的实验和理论方法，以确定和评估他们在该项目中合成和测试的材料的新分子设计策略。该项目还支持新的基于课程的本科生研究经验（CURE），让社区大学的学生进行与下一代太阳能设备相关的先进光子材料研究。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical DescriptionHarvesting solar energy efficiently and inexpensively is a grand challenge to producing clean, sustainable energy. The spectrum of light emitted by the sun spans a vast range, from the far infrared to ultraviolet. However only a fraction of this light can be absorbed by the active layer in a solar cell. If one can broaden the spectral range of sunlight that a solar panel can capture, the overall power generated increases. One strategy to increase the fraction of light absorbed is to combine two low-energy photons and fuse their energy into one higher-energy photon, a process called upconversion. The upconverted photon can then be absorbed and used to generate electricity from light that would otherwise be wasted. The goal of this project is to identify and design new molecules that can be used for upconversion in more efficient solar cells. Researchers will combine synthetic chemistry and optical characterization with theory and machine learning to achieve this goal. Beyond its scientific and technological impacts, participants will engage local and regional community college students with authentic and sustained exposure to original research experiences. One specific avenue the team is pursuing is to attempt to infuse photon upconversion research concepts into course-based academic laboratory experiments at a local community college. This approach to engage community college students with exposure to original research is intended to help overcome the geographic constraints that may hinder these students from taking part in more traditional research experience for undergraduate (REU) programs that require students to travel long distances to the research site.Technical DescriptionPhoton upconversion could significantly enhance solar cell efficiencies to routinely meet or exceed the Shockley-Queisser limit. One promising strategy for deploying photon upconversion to enhance the efficiency of solar photovoltaics is triplet-triplet annihilation upconversion because it can occur under low-intensity, non-coherent illumination from solar photons. Historically, the materials that have been explored for photon upconversion have included sensitizers based on precious metal complexes, arylhalides, and quantum dots. The first class is not economically viable due to the high cost of the metal, the second class is unstable under illumination, and the third class suffers from parasitic absorption of the upconverted light by the sensitizer. Given these materials constraints, the PI’s group identifies heavy-atom-free upconversion sensitizers based on thionated squaraine-based materials, which they explore as potential candidates for achieving NIR-to-visible photon upconversion for solar photovoltaic applications. The goal is to clarify elusive structure-function relationships that have historically made it challenging to identify NIR-absorbing triplet sensitizers in general, and more specifically, hitherto intractable to achieve NIR-to-Visible photon UC without using expensive precious metal centers or arylhalides that readily photodegrade, which are both unattractive for solar applications. One key goal of this work is to address specific questions such as, “What molecular descriptors are most prescriptive for simultaneously achieving NIR absorption and high intersystem crossing yields?” The team combines experimental and theoretical approaches based on ultrafast pump-probe spectroscopy, ab initio predictions, and reinforcement learning to identify and evaluate new molecular design strategies for materials that they synthesize and test in this project. The project also supports new Course-based Undergraduate Research Experiences (CUREs) for community college students to conduct advanced photonic materials research relevant for next-generation solar energy devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.