Charge Transport and Carrier-Phonon Interactions in Soft Lattice Metal Halide Perovskites

非技术描述金属卤化物钙钛矿是一类独特的“软”半导体，引起了人们的极大兴趣。它们可以在相对较低的温度下进行溶液处理，并已显示出在太阳能电池、发光二极管和辐射探测器等光电子器件方面的前景。然而，了解这些材料中的电荷传输仍然是难以捉摸的。由于离子运动和形成高质量电接触的困难，电荷传输的研究变得复杂。此外，钙钛矿在加工过程中或在其上沉积金属接触时可能会降解。这会导致过大的接触电阻并限制器件性能。通过将电极物理叠层到钙钛矿膜上，该团队将避免这种退化，并能够进行可靠的电学研究。他们将把对温度和光强的光电流和电容的研究与直接的结构分析结合起来。他们还将改变接触并使用掺杂来进一步调整载流子密度，并探索这些材料中的独特现象。这项系统的研究将揭开钙钛矿耐人寻味的特性，并开发出设计更高效设备所需的关键见解。相关研究活动还为学生提供了宝贵的教育机会，以培训下一代劳动力的相关技术。该项目利用独特的范德华集成策略，为金属卤化物钙钛矿(MHPS)的系统电传输研究创造了原子清洁的触点，并大大降低了接触电阻。通过将预制的原子扁平金属电极物理叠层到钙钛矿薄膜上，而不直接将钙钛矿暴露在任何光刻或沉积步骤中，这种方法可以有效地避免相关材料的降解，从而大大降低接触电阻，以便进行可靠的电传输研究。该项目将探测电荷输运和光载流子引起的局部晶格扭曲，相关的相变，以及它们对载流子动力学和基本输运性质的影响：包括与温度和光照相关的光导和光容研究，以探测载流子-声子相互作用，以及它们对载流子复合和输运性质的影响；直接结构分析，以研究不同光照或温度下与载流子产生相关的原子结构变化；开发不同的接触或选择性掺杂策略，以探测电子和空穴的输运特性；利用优化的器件制造和测量方案，探测低维MHPS和其他相关材料中的载流子-声子相互作用和铁电性；并通过化学掺杂、静电掺杂和光掺杂的组合进一步调整载流子浓度，以探测载流子-声子或载流子-载流子相互作用，并探索可能出现的现象。这些研究活动有助于对这类独特材料的基本光物理、电传输特性以及有趣的载流子-声子相互作用有一个批判性的理解，这不是以工程改进的光伏或发光二极管为目标，而是帮助从MHP释放新的技术潜力。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical DescriptionMetal halide perovskites are a unique class of “soft” semiconductors that have attracted enormous interest. They can be solution processed at relatively low temperatures and have shown promise for optoelectronic devices such as solar cells, light emitting diodes and radiation detectors. However, understanding charge transport in these materials remains elusive. Studies of charge transport are complicated by ion movement and the difficulty in forming high-quality electrical contacts. Furthermore, perovskites can degrade during processing or when depositing metal contacts on top of them. This results in excessive contact resistance and limits device performance. By physically laminating electrodes onto perovskite films, the team will avoid such degradation and be able to perform reliable electrical studies. They will combine studies of photocurrent and capacitance on temperature and light intensity with direct structural analysis. They will also vary contacts and use doping to further tailor the carrier density and explore unique phenomena in these materials. This systematic study will unravel the intriguing properties of perovskites and develop critical insights needed to design more efficient devices. The relevant research activities also offer valuable educational opportunities to students for training next generation of workforce in relevant technologies.Technical DescriptionThis project exploits a unique van der Waals integration strategy to create atomically clean contacts with greatly reduced contact resistance for a systematic electrical transport study of metal halide perovskites (MHPs). By physically laminating the prefabricated atomically flat thin film metal electrodes onto the perovskite thin films without directly exposing the perovskites to any lithography or deposition steps, this approach can effectively avoid the associated material degradations to achieve greatly reduced contact resistance for reliable electrical transport studies. The project will probe charge transport and photocarrier induced local lattice distortion, the associated phase transition, and their impact on the carrier dynamics and fundamental transport properties: including temperature- and illumination-dependent photo-conductance and photo-capacitance studies to probe carrier-phonon interactions, and their impact on the carrier recombination and transport properties; direct structural analysis to investigate the atomic structural change associated with the carrier generation under different illumination or temperature; developing different contacts or selective doping strategies to probe both electron and hole transport characteristics; using the optimized device fabrication and measurement protocols to probe the carrier-phonon interactions and ferroelectricity in low-dimensional MHPs and other related materials; and further tailoring the carrier density through a combination of chemical doping, electrical static doping and photodoping to probe carrier-phonon or carrier-carrier interactions and explore possible emergent phenomena. These research activities help develop a critical understanding of the fundamental photophysical, electrical transport properties, and the intriguing carrier-phonon interactions in this unique class of materials, which will not aim engineering improved photovoltaics or light-emitting diodes, but also help unlock new technological potentials from MHPs.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.