A vacancy‐ordered double perovskite, Cs2SnI6, has emerged as a promising lead‐free perovskite in the optoelectronic field. However, the charge transfer kinetics mediated by its surface state remains unclear. Here, the charge transfer mechanism of Cs2SnI6 is reported and the role of its surface state in the presence of a redox mediator is clarified. Specifically, charge transfer through the surface state of Cs2SnI6 and its subsequent surface state charging are demonstrated by cyclic voltammetry and Mott–Schottky measurements, respectively. Because it is expected that the surface state of Cs2SnI6 is capable of regenerating oxidized organic dyes, a Cs2SnI6‐based regenerator is developed for a dye‐sensitized solar cell composed of fluorine‐doped tin oxide (FTO)/dyed mesoporous TiO2/regenerator/poly(3,4‐ethylenedioxythiophene)/FTO. As expected, the performance of the Cs2SnI6‐based regenerator is strongly dependent on the highest occupied molecular orbital of the dyes. Consequently, Cs2SnI6 shows efficient charge transfer with a thermodynamically favorable charge acceptor level, achieving a 79% enhancement in the photocurrent density (14.1 mA cm−2) compared with that of a conventional liquid electrolyte (7.9 mA cm−2). The results suggest that the surface state of Cs2SnI6 is the main charge transfer pathway in the presence of a redox mediator and should be considered in future designs of Cs2SnI6‐based devices.

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The intramolecular charge transfer (ICT) of 1-aminoanthraquinone (AAQ) in the excited state strongly depends on its solvent properties, and the twisted geometry of its amino group has been recommended for the twisted ICT (TICT) state by recent theoretical works. We report the transient Raman spectra of AAQ in a dimethylsulfoxide (DMSO) solution by femtosecond stimulated Raman spectroscopy to provide clear experimental evidence for the TICT state of AAQ. The ultrafast (~110 fs) TICT dynamics of AAQ were observed from the major vibrational modes of AAQ including the νC-N + δCH and νC=O modes. The coherent oscillations in the vibrational bands of AAQ strongly coupled to the nuclear coordinate for the TICT process have been observed, which showed its anharmonic coupling to the low frequency out of the plane deformation modes. The vibrational mode of solvent DMSO, νS=O showed a decrease in intensity, especially in the hydrogen-bonded species of DMSO, which clearly shows that the solvation dynamics of DMSO, including hydrogen bonding, are crucial to understanding the reaction dynamics of AAQ with the ultrafast structural changes accompanying the TICT.

The structural changes during the intramolecular charge transfer (ICT) of nitroaromatic chromophores, 4-dimethylamino-4′-nitrobiphenyl (DNBP) and 4-dimethylamino-4′-nitrostilbene (DNS) were investigated by femtosecond stimulated Raman spectroscopy (FSRS) with both high spectral and temporal resolutions. The kinetically resolved Raman spectra of DNBP and DNS in the locally-excited and charge-transferred states of the S1 state appear distinct, especially in the skeletal vibrational modes of biphenyl and stilbene including ν8a and νC=C. The ν8a of two phenyls and the νC=C of the central ethylene group (only for stilbene), which are strongly coupled in the planar geometries, are broken with the twist of nitrophenyl group with the ICT. Time-resolved vibrational spectroscopy measurements and the time-dependent density functional theory simulations support the ultrafast ICT dynamics of 220–480 fs with the twist of nitrophenyl group occurring in the S1 state of the nitroaromatic chromophores. While the ICT of DNBP occurs via a barrier-less pathway, the ICT coordinates of DNS are strongly coupled to several low-frequency out-of-phase deformation modes relevant to the twist of the nitrophenyl group.

Cesium lead bromide perovskite nanocrystals (NCs) embedded in Cs4PbBr6 or CsPb2Br5 matrices forming a core/shell structures are promising luminescent materials that exhibit remarkable photoluminescence properties meeting a wide range of...