2 research outputs found
Organic dye-sensitized solar cells containing alkaline iodide-based gel polymer electrolytes: Influence of cation size
The electrolyte used in dye-sensitized solar cells (DSSCs) plays a key role in the process of current generation, and hence the analysis of charge-transfer mechanisms both in its bulk and at its interfaces with other materials is of fundamental importance. Because of solvent confinement, gel polymer electrolytes are more practical and convenient to use with respect to liquid electrolytes, but in-depth studies are still necessary to optimize their performances. In this work, gel polymer electrolytes of general formulation polyacrylonitrile (PAN)/ethylene carbonate (EC)/propylene carbonate (PC)/MI, where M+is a cation in the alkaline series Li-Cs, were prepared and used in DSSCs. Their ionic conductivities were determined by impedance analysis, and their temperature dependence showed Arrhenius behavior within the experimental window. FT-IR studies of the electrolytes confirmed the prevalence of EC coordination around the cations. Photo-anodes were prepared by adsorbing organic sensitizer D35 on nanocrystalline TiO2thin films, and employed to build DSSCs with the gel electrolytes. Nanosecond transient spectroscopy results indicated a slightly faster dye regeneration process in the presence of large cations (Cs+, Rb+). Moreover, a negative shift of TiO2flat-band potential with the decreasing charge density of the cations (increasing size) was observed through Mott-Schottky analysis. In general, results indicate that cell efficiencies are mostly governed by photocurrent values, in turn depending on the conductivity increase with cation size. Accordingly, the best result was obtained with the Cs+-containing cell, although in this case a slight reduction of photovoltage compared to Rb+was observed
Ultrafast collapse of molecular polaritons in photoswitch-nanoantennas at room temperature
Molecular polaritons are hybrid light-matter states that emerge when a
molecular transition strongly interacts with photons in a resonator. At optical
frequencies, this interaction unlocks a way to explore and control new chemical
phenomena at the nanoscale. Achieving such a control at ultrafast timescales,
however, is an outstanding challenge, as it requires a deep understanding of
the dynamics of the collectively coupled molecular excitation and the
nanoconfined electromagnetic fields. Here, we investigate the dynamics of
collective polariton states, realized by coupling molecular photoswitches to
optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an
ultrafast collapse of polaritons to a single-molecule transition triggered by
femtosecond-pulse excitation at room-temperature. Through a synergistic
combination of experiments and quantum mechanical modelling, we show that the
response of the system is governed by intramolecular dynamics, occurring one
order of magnitude faster with respect to the unperturbed excited molecule
relaxation to the ground state