Atomic-Scale Perspective of Ultrafast Charge Transfer at a Dye–Semiconductor Interface

Abstract

Understanding interfacial charge-transfer processes on the atomic level is crucial to support the rational design of energy-challenge relevant systems such as solar cells, batteries, and photocatalysts. A femtosecond time-resolved core-level photoelectron spectroscopy study is performed that probes the electronic structure of the interface between ruthenium-based N3 dye molecules and ZnO nanocrystals within the first picosecond after photoexcitation and from the unique perspective of the Ru reporter atom at the center of the dye. A transient chemical shift of the Ru 3d inner-shell photolines by (2.3 ± 0.2) eV to higher binding energies is observed 500 fs after photoexcitation of the dye. The experimental results are interpreted with the aid of ab initio calculations using constrained density functional theory. Strong indications for the formation of an interfacial charge-transfer state are presented, providing direct insight into a transient electronic configuration that may limit the efficiency of photoinduced free charge-carrier generation.

Ultrafast carrier thermalization and trapping in silicon-germanium alloy probed by extreme ultraviolet transient absorption spectroscopy

“…The general similarities between the transients of germanium and silicon-germanium [Fig. 3(b)] strongly corroborate that the reporter atom concept 20 is successfully applied here to solids and that germanium atoms can be employed to probe the carrier dynamics of electrons and holes in the Si-like indirect gap alloy. Other recent findings by Santomauro et al 40 suggest that this is expected to be true for carriers that are either localized near the germanium atoms or delocalized in the alloy.…”

“…The samples are nanocrystalline with domain sizes of ∼2.5 nm, grown by low-pressure chemical vapor deposition (LPCVD). Herein, the germanium atoms are employed as reporter atoms 20 for probing the carrier dynamics in the alloy with sensitivity to electrons and holes. The transient absorption (TA) data is captured at the M 4,5 -edge of the germanium atoms in the silicon-germanium alloy and, by decomposing the TA data into contributions of electronic state blocking of optically excited carriers and band shifts, the carrier dynamics are retrieved (see also supplementary material, Sec.…”

Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer

“…However, pioneering PES experiments on solids at FELs have revealed several experimental challenges 14–16 . A very recent time resolved PES study of charge transfer on a molecular dye absorbed on a surface has shown the possibility of performing dynamical chemical analysis at FELs; 17 however, the application to other systems requires a detailed study due to the difficulties in the data interpretation because of modifications in the PES spectra known as vacuum space charge effects 18 . In particular, the electrons photoemitted from the sample within the duration of a femtosecond X-ray pulse can be described as enclosed in a cloud of charges originated from the sample and travelling to the analyser 18 .…”

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups

“…Our results point in the same direction as recently published measurements that showed the formation of a transient electronic configuration that gives rise to a distribution of transition states. 12 They have two implications for applications: first, the transient configuration can present a bottle-neck for HET as discussed by Siefermann et al 12 Second, it gives the opportunity to independently design a favorable chromophore and adjust the level alignment by introducing dipole groups that shift the donor level just above the conduction band edge and thus optimizes open circuit voltage for the respective chromophore without altering charge separation efficiency. A similar result has been presented recently.…”