Photoexcited Carrier Dynamics in Oxide Semiconductors for Photovoltaics

智能优点半导体钙钛矿氧化物是由地球上丰富的无毒元素制成的，可以在高质量的异质结构中合成，并且具有可以通过掺杂进行调节的电子性质。虽然这些性质使它们成为太阳能转换的有前途的候选材料，但在利用复合氧化物进行高效的太阳能转换之前，必须有基本的科学见解，如了解限制光激载流子复合寿命的机制。该项目的智能使命是确定利用先进的薄膜沉积和超快光谱相结合的方法来最大化光激发载流子寿命和迁移率的策略。利用氧化物分子束外延技术合成了由ABO_3钙钛矿结构组成的薄膜异质结构，其中A为稀土或碱土离子，B为过渡金属离子(A=Sr，La，Eu；B=Cr，Fe)。温度相关的时间分辨太赫兹光谱(TRTS)、紫外/可见光瞬时吸收(TA)光谱和霍尔效应测量将被用来探测钙钛矿薄膜中光激发载流子的动力学和迁移率。通过对钙钛矿光物理的详细研究，为新一代基于氧化物的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太阳能转换提供合理的基础。由地球上丰富的无毒材料制成的高效、低成本、清洁和可持续的光伏和光催化剂的可获得性将对美国的能源组合产生革命性影响。该项目将通过对研究生和本科生进行材料合成和表征技术培训、学生参加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促进科学教育。PIS也会将外展扩展到大学预科学生吗？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利，因为大多数教师来自费城学区，那里的学生群体中有80%以上是少数族裔。

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.