Ultrafast terahertz spectroscopy provides insight into charge transfer efficiency and dynamics in artificial photosynthe
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ORIGINAL ARTICLE
Ultrafast terahertz spectroscopy provides insight into charge transfer efficiency and dynamics in artificial photosynthesis Uriel T. Tayvah1 · Jens Neu2 · Jacob A. Spies1 · Charles A. Schmuttenmaer1 · Gary W. Brudvig1,2 Received: 15 September 2020 / Accepted: 11 November 2020 © Springer Nature B.V. 2020
Abstract Terahertz (THz) spectroscopy provides a noncontact method to measure the ultrafast dynamics and photoconductivity of mobile carriers in semiconducting materials. This has proven useful in studying artificial photosynthesis devices which use semiconductor photoelectrodes. We present a brief introduction to optical-pump THz-probe (OPTP) spectroscopy, a technique that provides unique and useful insight into interfacial electron transfer (from the surface-attached dye to the conduction band of the semiconductor) in dye-sensitized photoelectrochemical cells. Compared with more familiar methods like visible transient absorption spectroscopy, OPTP spectroscopy stands out in offering both sub-picosecond time resolution as well as sensitivity to mobile carriers (electrons and holes) in the semiconductor portion of artificial photosynthesis devices. The mobile carriers are crucial to device performance as only they pass to the other half cell to complete the reaction. In order to highlight these advantages and illustrate the types of questions OPTP spectroscopy can address, we discuss three case studies. In the first, OPTP spectroscopy is used to measure the injection rates from a set of six different dyes, revealing the effect of the energetics and lifetimes of the dye excited states on interfacial electron transfer. The subsequent case studies investigate the influence of varying the moieties which bind to the surface (anchors), as well as the moieties that connect the chromophore with these anchors (linkers). OPTP spectroscopy was used to measure the interfacial electron transfer rate as these moieties were varied. Keywords Terahertz spectroscopy · Artificial photosynthesis · Charge transfer · Ultrafast
Introduction Photosynthesis—both natural and artificial—relies on photochemically generating excited states and channeling their energy toward reaction centers in order to utilize it to drive the desired charge-separation reactions. This process typically involves a series of fast electron transfer events. These charge transfer events are crucial in creating and maintaining Charles A. Schmuttenmaer: deceased. * Uriel T. Tayvah [email protected]
charge separation, which is an important facet of the function and efficacy of photosynthetic systems. In order to gain insight into charge transfer, a range of techniques can be used, each with their own advantages and limitations. This paper focuses on artificial photosynthesis, highlighting a less well-known technique—ultrafast terahertz (THz) spectroscopy—that has proven valuable in the field. We will first compare it with other techniques used to probe charge transfer, and then discuss past work from our group which demonstrates the ut
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