Boucher Dylan G, Kearney Kara, Ertekin Elif, Rose Michael J
Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States.
Department of Mechanical Science and Engineering, University of Illinois, Urbana, Illinois 61801, United States.
J Am Chem Soc. 2021 Feb 17;143(6):2567-2580. doi: 10.1021/jacs.0c12075. Epub 2021 Feb 3.
Photoelectrochemical (PEC) device efficiency depends heavily on the energetics and band alignment of the semiconductor|overlayer junction. Exerting energetic control over these junctions via molecular functionalization is an extremely attractive strategy. Herein we report a study of the structure-function relationship between chemically functionalized pSi(111) and the resulting solar fuels performance. Specifically, we highlight the interplay of chemical structure and electronic coupling between the attached molecule and the underlying semiconductor. Covalent attachment of aryl surface modifiers (phenyl, Ph; nitrophenyl, PhNO; anthracene, Anth; and nitroanthracene, AnthNO) resulted in high-fidelity surfaces with low defect densities ( < 50 cm/s). Electrochemical characterization of these surfaces in contact with methyl viologen resulted in systematically shifted band edges (up to 0.99 V barrier height) and correspondingly high photoelectrochemical performance ( up to 0.43 V vs MV) consistent with the introduction of a positive interfacial dipole. We extend this functionalization to HER conditions and demonstrate systematic tuning of the HER using pSi(111)-R|TiO|Pt architecture. Correlation of the shifts in barrier height with the photovoltage provides evidence for nonideality despite low surface recombination. Critically, DFT calculations of the electronic structure of the organic-functionalized interfaces show that the molecule-based electronic states effectively hybridized with the silicon band edges. A comparison of these interfacial states with their isolated molecular analogues further confirms electronic coupling between the attached molecule and the underlying semiconductor, providing an induced density of interfacial states (IDIS) which decreases the potential drop across the semiconductor. These results demonstrate the delicate interplay between interfacial chemical structure, interfacial dipole, and electronic structure.
光电化学（PEC）器件的效率在很大程度上取决于半导体|覆盖层结的能量学和能带排列。通过分子功能化对这些结进行能量控制是一种极具吸引力的策略。在此，我们报告了一项关于化学功能化的pSi(111)与所得太阳能燃料性能之间结构-功能关系的研究。具体而言，我们强调了附着分子与底层半导体之间化学结构和电子耦合的相互作用。芳基表面改性剂（苯基，Ph；硝基苯基，PhNO；蒽，Anth；和硝基蒽，AnthNO）的共价附着产生了具有低缺陷密度（<50 cm/s）的高保真表面。这些与甲基紫精接触的表面的电化学表征导致能带边缘系统地移动（高达0.99 V的势垒高度），并且相应地具有高光电化学性能（相对于MV高达0.43 V），这与正界面偶极的引入一致。我们将这种功能化扩展到析氢反应（HER）条件，并展示了使用pSi(111)-R|TiO|Pt结构对HER进行系统调节。势垒高度的变化与光电压的相关性提供了尽管表面复合率低但仍存在非理想性的证据。至关重要的是，有机功能化界面电子结构的密度泛函理论（DFT）计算表明，基于分子的电子态与硅能带边缘有效地杂化。将这些界面态与其孤立的分子类似物进行比较，进一步证实了附着分子与底层半导体之间的电子耦合，提供了一个界面态诱导密度（IDIS），它降低了半导体上的电势降。这些结果证明了界面化学结构、界面偶极和电子结构之间微妙的相互作用。
