Materials and Interface Engineering for Highly Efficient and Stable 2D/3D Tin Pseudohalide Perovskite Solar Cells

光伏（PV）技术是一种可持续的清洁能源，能够满足我们日益增长的能源需求。混合有机-无机卤化铅钙钛矿太阳能电池（PSC）在过去十年中已经成为一种有前途的低成本薄膜太阳能电池，具有高效率和卷对卷印刷可加工性，这可以鼓励向清洁能源经济过渡。然而，铅的使用引起了商业化的关注，因为潜在的环境污染和人类健康问题。重要的是要仔细找到一种环境友好且有效的铅替代品，重点是保持钙钛矿材料中铅的优异性能。锡钙钛矿被认为是替代铅钙钛矿的理想候选者，根据Shockley-Queisser极限，锡PSC的理论PCE接近30%。尽管已经取得了进展，但锡PSC的效率和稳定性仍然不如其铅对应物。该项目将通过材料和界面工程应用协同方法，目标是减少缺陷，抑制锡氧化，增强电荷提取和传输，减少能量损失，从而提高锡PSC的效率和稳定性。该项目的成功将推进离子半导体材料和薄膜太阳能电池器件物理学的知识，这可能导致向清洁能源经济的过渡，因为无铅，高效和稳定的PSC具有潜在的商业化潜力。来自代表性不足群体的研究生和本科生将在这个高度跨学科的研究项目中接受培训。从这项工作中获得的知识将通过PI小组将在康奈尔大学校园和伊萨卡科学中心举办的年度活动“扩大你的视野”的研讨会进行传播，为年轻学生及其家庭提供动手活动和演示。锡基PSC的挑战主要是由于锡缺陷，导致光载流子和金属导电性的不期望的非辐射复合，以及伴随的开路电压损失。此外，表面和晶界上的悬挂键引入陷阱态，其作为非辐射复合和降解位点的中心。该研究团队旨在（1）开发新型Dion-Jacobson（DJ）相二维和三维（2D/3D）锡拟卤化物钙钛矿，以减少锡缺陷并钝化晶界和表面的缺陷;（2）通过引入官能团来引导钙钛矿生长并减少界面陷阱态，合成新的空穴传输材料;以及（3）在锡PSC中部署新的空穴和电子传输材料以增加器件效率和稳定性。形成DJ相2D/3D混合锡钙钛矿代表了应对锡基PSC的效率和稳定性挑战的范式转变。我们的理论依据是：（1）采用大的A '位二价阳离子和类卤阴离子形成2D/3D异质结锡钙钛矿，可以显著减少缺陷，有效抑制锡的氧化;以及（2）通过利用新开发的空穴和电子输运，可以显著降低能量损失，并且可以大大提高器件的稳定性材料，以分别引导钙钛矿生长和钝化缺陷。通过从根本上理解DJ相2D/3D锡赝卤化物钙钛矿的结构和光电性能、功能化空穴传输层对钙钛矿生长的影响以及非富勒烯受体与钙钛矿的相互作用，可以阐明指导开发高效、稳定的锡PSC的一般原则，这可能导致清洁能源技术的转变 。NSF的法定使命，并已被认为是值得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的支持。

Photovoltaic (PV) technology is sustainable, clean source of energy with the capacity to fulfill our growing energy needs. Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have emerged in the past decade as a promising low-cost, thin film solar cell with high efficiency and roll-to-roll printing processability, which could encourage a transition into a clean energy economy. However, the use of lead raises the concerns for commercialization because of the potential environmental contamination and human health problems. It is important to carefully find an environmentally benign and efficient replacement for lead with a focus on keeping the excellent properties ascribed to its presence in perovskite materials. Tin perovskite is regarded as an ideal candidate to replace lead perovskite with the theoretical PCE of tin PSCs close to 30% according to Shockley-Queisser limit. Despite progress having been made, the efficiency and stability of tin PSCs are still inferior to their lead counterparts. This project will apply a synergetic approach via materials and interface engineering with the goal to reduce defects, suppress tin oxidization, enhance charge extraction and transport, and reduce energy losses, hence, to increase the efficiency and stability of tin PSCs. Success in this project will advance the knowledge of ionic semiconducting materials and device physics of thin film solar cells, which could lead to a transition into a clean energy economy because of potential commercialization of lead-free, highly efficient and stable PSCs fabricated with low-temperature, large-area, high-throughput processes. Graduate and undergraduate students from underrepresented groups will receive training in this highly interdisciplinary research project. The knowledge gained from this work will be disseminated through the workshop that the PI group will offer to the annual event of Expanding Your Horizons at Cornell campus and Ithaca Sciencenter by providing hands-on activities and demonstrations for young students and their families. The challenge with tin-based PSCs is primarily due to tin-defects, resulting in the undesirable nonradiative recombination of photocarriers and metallic conductivity, and the attendant loss of open-circuit voltage. Additionally, the dangling bonds on the surface and at the grain boundaries introduce trap states, which act as the centers of nonradiative recombination and degradation sites. The research team aims to (1) develop novel Dion-Jacobson (DJ) phase two-dimensional and three-dimensional (2D/3D) tin pseudohalide perovskites to reduce tin defects and passivate defects at the grain boundaries and surfaces; (2) synthesize new hole transport materials by introducing functional groups to guide perovskite growth and reduce interface trap states; and (3) deploy new hole and electron transport materials in tin PSCs to increase device efficiency and stability. Forming DJ phase 2D/3D hybrid tin perovskites represents a paradigm shift in tackling the challenge of efficiency and stability of tin-based PSCs. The intellectual merit is driven by our hypotheses: (1) the defects can be significantly reduced and the tin oxidation can be effectively suppressed by adopting large A’-site divalent cations and pseudohalide anions to form 2D/3D bulk and planar heterojunction tin perovskites; and (2) the energy losses can be significantly reduced and the device stability can be greatly enhanced by utilizing newly developed hole and electron transport materials to guide perovskite growth and passivate defects, respectively. By fundamentally understanding the structural and optoelectronic properties of DJ phase 2D/3D tin pseudohalide perovskites, the effect of functionalized hole transport layer on the growth of perovskites, and the non-fullerene acceptor interaction with perovskites, the general principles to guide the development of highly efficient, stable tin PSCs can be elucidated, which could lead to the transformation of clean energy techniques. 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.