Photophysics and Electron Dynamics in Dye-Sensitized Semiconductor Film Studied by Time-Resolved Mid-IR Spectroscopy

Abstract

Photophysics and electron dynamics in dye-sensitized semiconductor film were studied by transient mid-IR spectroscopy, in particular on the nano- to millisecond time scale. As sensitizers, a Ru complex and 9-phynol xanthane derivatives were used. We simultaneously observed electrons injected into the conduction band of a semiconductor and the change of vibration bands due to formation of a cation of a dye molecule. The transient absorption components derived from these two species decayed differently. From this observation, we found that injected electrons decay through two paths; one was back electron transfer, and the other was decay to deep trap sites that cannot be detected by mid-IR light. We could also estimate the amount of electron injection for different dye-sensitized TiO2. Our transient mid-IR spectroscopy in long time scale introduces a semi-new approach to the slow dynamics in dye-sensitized semiconductors including back electron transfer.

Quantum Dynamics of Photoinduced Electron-Transfer Reactions in Dye−Semiconductor Systems: First-Principles Description and Application to Coumarin 343−TiO2

“…In particular, the process of electron injection from an electronically excited state of a dye molecule into a semiconductor substrate has been investigated in great detail experimentally in recent years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] This process represents a key step for photonic energy conversion in nanocrystalline solar cells. 2,6,9,18,19 Employing femtosecond spectroscopy techniques, it has been demonstrated that electron-injection processes at dye-semiconductor interfaces often take place on an ultrafast (sub-picosecond) time scale.…”

Time-resolved Infrared Absorption Study of Photochemical Reactions Over Metal Oxides

“…This leads to an advanced understanding of the post-injection processes. Figure 7 shows a typical spectrum , of a dye-sensitized film [33]. A thin film of TiO 2 (P-25) was fixed on a CaF 2 plate and then dipped into a solution of N3: Ru(dcbpy) 2 (NCS) 2 with dcbpy ¼ 4,4 0 -dicarboxy-2,2 0 -bipyridine.…”

“…Little is known about the kinetics of charges excited Figure 9. The occupation ratio of the three states, e l : shallow traps in the oxide, e 2 : deep traps, and e 3 : neutralized N3 dye [33].…”

“…The inset shows the absorption spectrum and how the contribution of the cationized dye (C) was deduced[33].…”

Time-resolved Spectroscopic Study on Photocarrier Generation Process in Layered Organic Photoconductors

“…The authors and other co-workers have developed a system which can detect transient absorbance change as small as 10 −6 over a wide wavelength range (700-10000 nm) and also over a wide range of delay time (50 ns -1 s) [5][6][7]. This sensitive system enabled us to detect carrier species with a weak excitation light.…”