We carried out a time-resolved charge extraction (TRCE) study on the charge recombination dynamics of open-circuit dye-sensitized solar cells (DSSCs) by examining the temporal evolution of electron density with varying the concentration of the electrolyte component tert-butylpyridine (TBP). The charge recombination dynamics extracted from TRCE results exhibit distinctly different temporal behavior depending on the photovoltage or electron density. We proposed a theoretical model of electron density dependent charge recombination, which unifies the transport- and transfer-limited charge recombination mechanisms. This model, as rationalized by transient photovoltage (TPV) kinetics, can account well for the TRCE results. The relevance between electron transport and charge transfer in the recombination process was unraveled, and the electron density dependent pathway of charge recombination was elucidated.

TiO2 polydisperse mesoporous spheres (PMSs) and nanocrystals were selectively prepared via slightly altering the precursor dosage in a solvothermal reaction. Afterwards, the submicrometer-sized PMSs and nanocrystals were adopted as sample materials to shed light on the effect of the photoanode structure over the performance of CdS/CdSe-cosensitized solar cells by comparing four types of photoanode structures: nanocrystal film, blend film, bilayer film and PMSs film. It was found that the bilayer photoanode could promote the harvesting of incident light by increasing both the CdS/CdSe QDs loading amount and the scattering effect. According to the transient photovoltage measurements, the carrier recombination at the TiO2/electrolyte and FTO/electrolyte interfaces were substantially passivated in the bilayer cell. Moreover, a high electron diffusion rate of 142.0 × 10−9 m2 s−1 was also obtained in the bilayer cell, indicating high photoelectrons collection efficiency in the film structure. Therefore, the bilayer cell can well integrate the structural advantages of the PMSs and nanocrystals, which contributes to a high conversion efficiency of 4.70%, demonstrating a ∼54% and ∼12% improvement compared with the cells derived from nanocrystal and PMSs, respectively.

The density of state (DOS) of intra-gap traps and the dynamics of electron transport of a dye-sensitized TiO2 solar cell were investigated by means of time-resolved charge extraction (TRCE). The intrinsic chemical capacitance of the TiO2 layer was separated from the parasitic capacitance of the FTO electrode, and was found to be dependent biexponentially on the photovoltage. It was shown that the shallow traps (>700 meV) differ from the deep ones (<350 meV) by the respective characteristic energy of 48 meV and 765 meV, and that the amount of shallow traps is more than an order of magnitude larger than that of the deep ones. Our results support the mechanism of shallow-trap dominant multiple-trap limited charge transport, and suggest a substantial margin for the short-circuit photocurrent density to reach its theoretical limit.

•We provided the long-sought characteristic absorption spectra of radical anionic P3HT.•We found the novel role of polymer–fullerene interface in breaking the electron–hole symmetry of the crystalline P3HT phase.•We revealed the intrinsic anisotropic hole and electron conductivities of the crystalline P3HT phases.To investigate the effect of film morphology on the electronic structures of anionic and cationic polarons of poly(3-hexylthiophene), P3HT•− and P3HT•+, we have characterized the subgap optical absorption of these polaronic species by means of spectroelectrochemistry. For the pristine films of regiorandom (RRa) P3HT or its blend with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), both the ground-state bleaching and the subgap absorption of RRa-P3HT•− resemble closely to those of RRa-P3HT•+. For the solvent vapor annealed neat film of regioregular (RR) P3HT, RR-P3HT•− shows distinctly different absorption spectra from RR-P3HT•+, and the difference is substantially enhanced by mixing up with PC61BM. The spectral differences are ascribed to the effects of the boundaries among the polymer phases and the polymer–fullerene interfaces. With respect to the neat RR-P3HT film, the RR-P3HT/PC61BM blend exhibits a 0.05–0.06 eV downshift of the SOMO levels for both types of polarons, implying the anisotropic hole and electron conductivities of crystalline RR-P3HT phases, which may play important roles in the transport and photogeneration of free charge carriers.

The interactions between cationic meso-tetrakis(4-(N-methylpyridiumyl))porphyrin (TMPyP4) and the G-quadruplex (G4) of human telomeric single-strand oligonucleotide d(TTAGGG)2 (S12) have been investigated by means of circular dichroism (CD), UV–visible absorption and fluorescence spectroscopies. It is found that TMPyP4 can preferentially induce the conformational conversion of the G4 structure from the parallel type to the parallel/antiparallel mixture in the presence of K+, and that it can directly induce the formation of antiparallel G4 structure from the single-strand oligonucleotide S12 in the absence of K+. Furthermore, the comparable experiments of TMPyP4 with two single-strand oligonucleotides S6 d(TTAGGG) and S24 d(TAGGG(TTAGGG)3T) in the absence of K+ show that TMPyP4 can also induce the formation of antiparallel G4 from S24 but not from S6, indicating that the end-loops of the G4 structure are the key factors for the formation of G4 induced by TMPyP4.

We have performed systematic spectroscopic titrations to characterize the binding reaction of cationic meso-tetrakis(4-(N-methylpyridiumyl))porphyrin (TMPyP4) with the G-quadruplex (G4) of human telomeric single-strand oligonucleotide d[TAGGG(TTAGGG)3T] (S24), for which special effort was made to examine the TMPyP4-G4 binding stoichiometry, the binding modes, and the conformational conversion of the G4 structure under different potassium ion (K+) concentration. It is found that, in the presence of 0, 10 mM, and 100 mM K+, TMPyP4 forms a complex with the anti-parallel G4 in a TMPyP4-to-G4 molar ratio of 5, 5 and 3, respectively, and the increase of K+ concentration would reduce the binding affinity of TMPyP4 to G4. For the TMPyP4–G4 complex, the end-stacking mode and groove binding mode were presumed mainly by the results of time-resolved fluorescence spectroscopy in the three cases. Most importantly, it is found that TMPyP4 can directly induce the formation of the anti-parallel G4 structure from the single-strand oligonucleotide S24 in the absence of K+, and that it can preferentially induce the conformational conversion of the G4 structure from the hybrid-type to the anti-parallel one in the presence of K+.

Here, we report the surface-enhanced Raman scattering (SERS) spectrum of 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (Tinuvin P), a benzotriazole derivative that is the most widely used commercially available UV absorber or stabilizer and is used representatively for the research of photostability mechanism. A full assignment of the Raman spectrum has been made based on the scaled-DFT analysis of the normal vibrational modes. Through the comparative studies on the ordinary Raman spectrum and the SERS spectrum of Tinuvin P, we propose that this molecule binds the Au atom, via the O atom of the hydroxyl or the N1 atom of the benzotriazole moiety, with a perpendicular geometry.

TiO2 polydisperse mesoporous spheres (PMSs) and nanocrystals were selectively prepared via slightly altering the precursor dosage in a solvothermal reaction. Afterwards, the submicrometer-sized PMSs and nanocrystals were adopted as sample materials to shed light on the effect of the photoanode structure over the performance of CdS/CdSe-cosensitized solar cells by comparing four types of photoanode structures: nanocrystal film, blend film, bilayer film and PMSs film. It was found that the bilayer photoanode could promote the harvesting of incident light by increasing both the CdS/CdSe QDs loading amount and the scattering effect. According to the transient photovoltage measurements, the carrier recombination at the TiO2/electrolyte and FTO/electrolyte interfaces were substantially passivated in the bilayer cell. Moreover, a high electron diffusion rate of 142.0 × 10−9 m2 s−1 was also obtained in the bilayer cell, indicating high photoelectrons collection efficiency in the film structure. Therefore, the bilayer cell can well integrate the structural advantages of the PMSs and nanocrystals, which contributes to a high conversion efficiency of 4.70%, demonstrating a ∼54% and ∼12% improvement compared with the cells derived from nanocrystal and PMSs, respectively.