Photoexcited Carrier Dynamics in Oxide Semiconductors for Photovoltaics

半导体钙钛矿氧化物由地球上丰富的无毒元素制成，可以合成高质量的异质结构，并具有可以通过掺杂调整的电子特性。虽然这些特性使它们成为太阳能转换的有希望的候选者，但在复杂氧化物可用于有效的太阳能转换之前，需要基本的科学见解，例如理解限制光激发载流子的复合寿命的机制。该项目的智力使命是确定策略，以最大限度地提高光激发载流子的寿命和流动性，使用先进的薄膜沉积和超快光谱的组合。 将使用氧化物分子束外延合成由ABO 3钙钛矿结构组成的薄膜异质结构，其中A是稀土或碱土离子，B是过渡金属离子（A = Sr、La、Eu; B = Cr、Fe）。 温度依赖的时间分辨太赫兹光谱（TRTS），紫外/可见瞬态吸收（TA）光谱，和霍尔效应测量将用于探测光激发载流子的动态和钙钛矿薄膜的迁移率。通过对钙钛矿晶体物理的详细研究，这项工作将为新一代氧化物基太阳能转换器件奠定科学基础。 更广泛的影响该项目将为设计和选择具有长寿命，高载流子迁移率和最佳带隙的新型钙钛矿氧化物提供合理的基础。 由地球上丰富的无毒材料制成的高效、低成本、清洁和可持续的光催化剂和光催化剂的可用性将对美国的能源组合产生变革性影响。该项目将通过包括材料合成和表征技术的研究生和本科生培训，学生参与科学会议以及薄膜沉积和超快光谱设备的课堂演示等活动来推进科学教育。外展也将扩大到大学预科学生的PI？通过NSF RET和大学发起的项目继续参与指导当地高中教师。 这些计划对代表性不足的群体特别有益，因为大多数教师来自费城学区，其学生超过80%是少数民族。

Intellectual MeritSemiconducting perovskite oxides are made from earth-abundant, non-toxic elements, can be synthesized in high quality heterostructures, and have electronic properties that can be tuned through doping. While these properties make them promising candidates for solar energy conversion, fundamental scientific insights, such as understanding the mechanisms that limit recombination lifetime of photoexcited carriers, are necessary before complex oxides can be utilized for efficient solar energy conversion. The intellectual mission of this project is to identify strategies to maximize photoexcited carrier lifetime and mobility using a combination of advanced thin film deposition and ultrafast spectroscopy. Thin film heterostructures consisting of the ABO3 perovskite structure, where A is a rare earth or alkaline earth ion and B is a transition metal ion (A = Sr, La, Eu; B = Cr, Fe), will be synthesized using oxide molecular beam epitaxy. Temperature-dependent time resolved terahertz spectroscopy (TRTS), UV/visible transient absorption (TA) spectroscopies, and Hall effect measurements will be used to probe dynamics of photoexcited carriers and mobility in the perovskite thin films. Through this detailed study of perovskite photophysics, this work will lay the scientific foundation for a new generation of oxide-based solar energy conversion devices. Broader ImpactThis project will provide a rational basis for designing and selecting new perovskite oxides with long lifetimes, high carrier mobilities, and optimal band gaps for solar energy conversion. Availability of efficient, low-cost, clean, and sustainable photovoltaics and photocatalysts made from earth-abundant, non-toxic materials would have transformative impact on the US energy portfolio. The project will advance scientific education through activities including the training of graduate and undergraduate students in materials synthesis and characterization techniques, student participation in scientific conferences, and in-class demonstrations of thin film deposition and ultrafast spectroscopy equipment. Outreach will also extend to pre-college students by the PIs? continued participation in mentoring local high school teachers through NSF RET and university-initiated programs. These programs are particularly beneficial for underrepresented groups since most teachers are from the School District of Philadelphia, whose student body is over 80% minorities.