Skiba Emily J, Buckner Haley B, Lee Channyung, McKnight Grace, Wallick Rachel F, van der Veen Renske, Ertekin Elif, Perry Nicola H
Department of Materials Science & Engineering, University of Illinois, Urbana-Champaign, 1304 W. Green St., Urbana, Illinois 61801, United States.
Materials Research Laboratory, 104 S. Goodwin Ave., Urbana, Illinois 61801, United States.
J Am Chem Soc. 2024 Aug 21;146(33):23265-23277. doi: 10.1021/jacs.4c05764. Epub 2024 Aug 6.
Enabling light-controlled ionic devices requires insight into photoionic responses in technologically relevant materials. Mixed-conducting perovskites containing nondilute Fe─serving as electrodes, catalysts, and sensors─can support large, electronically accommodated excursions in oxygen content, typically controlled by temperature, bias, and gas atmosphere. Instead, we investigated the ability of low-fluence, above-bandgap illumination to adjust oxygen stoichiometry and drive oxygen fluxes in nondilute Sr(TiFe)O ( = 0.07, 0.35) thin films with high baseline hole concentrations. Films' optical transmission at 2.8 eV was used as a probe of oxygen stoichiometry in the range ∼100-500 °C. We compared pO-step-driven and UV (3.4 eV)-step-driven visible optical transmission relaxations in films, finding that the time constants and activation energies of the relaxations were consistent with each other and thus with oxygen-surface-exchange-limited kinetics. Blocking oxygen exchange at the solid-gas interface with a UV-transparent capping layer resulted in no UV-induced optical relaxations. These results demonstrate that above-bandgap illumination can increase oxygen content in nondilute compositions through oxygen flux into the solid from the gas. First-principles simulations of defect formation enthalpies indicate that oxygen vacancies are energetically less favorable under steady-state illumination owing to shifts in quasi-Fermi levels. A larger 2.8 eV-optical response to UV illumination in = 0.07 vs = 0.35 samples was further investigated through ultrafast transient spectroscopy, where it was found that the = 0.07 sample exhibits a slower carrier recombination. Together, these results suggest potential design principles for materials supporting large stoichiometry changes under above-gap illumination: (1) long excited carrier lifetimes and (2) highly charged, rather than neutral, defects/associates.
实现光控离子器件需要深入了解技术相关材料中的光离子响应。含有非稀释铁的混合导电钙钛矿——用作电极、催化剂和传感器——可以支持氧含量的大幅电子调节变化，通常由温度、偏压和气体气氛控制。相反，我们研究了低通量、高于带隙光照调节非稀释Sr(TiFe)O（ = 0.07, 0.35）薄膜中氧化学计量并驱动氧通量的能力，这些薄膜具有高基线空穴浓度。薄膜在2.8 eV处的光透射率被用作在约100 - 500 °C范围内氧化学计量的探针。我们比较了薄膜中pO阶跃驱动和紫外（3.4 eV）阶跃驱动的可见光学透射率弛豫，发现弛豫的时间常数和活化能彼此一致，因此与氧表面交换受限动力学一致。用紫外透明覆盖层阻断固 - 气界面处的氧交换导致没有紫外诱导的光学弛豫。这些结果表明，高于带隙光照可以通过氧从气体流入固体来增加非稀释成分中的氧含量。缺陷形成焓的第一性原理模拟表明，由于准费米能级的移动，在稳态光照下氧空位在能量上不太有利。通过超快瞬态光谱进一步研究了 = 0.07与 = 0.35样品中对紫外光照的更大的2.8 eV光学响应，发现 = 0.07样品表现出较慢的载流子复合。总之，这些结果提出了在高于带隙光照下支持大化学计量变化的材料的潜在设计原则：（1）长激发载流子寿命和（2）高电荷而非中性的缺陷/缔合体。
