Tailoring the Vertical Morphology of Organic Films for Efficient Planar-Si/Organic Hybrid Solar Cells by Facile Nonpolar Solvent Treatment

The optical and electrical properties of the blending organic film poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) are strongly affected by its morphology, resulting in the performance variation in Si/organic hybrid solar cells. Here, a facile postsolvent treatment is used to tailor the vertical morphology of PEDOT:PSS by introducing a nonpolar solvent. X-ray photoelectron spectroscopy depth-profiling measurements show that the distribution of PEDOT and PSS on the surface of n-type Si can be changed by nonpolar solvent n-hexane (NHX) treatment, where more PSS aggregate at the bottom of the blend film and more PEDOT float up to the top, as compared with the reference sample. As a result, after NHX treatment, the average lifetime of the Si/organic films is increased from 152 μs for untreated samples to 248 μs for NHX-treated ones because of the better passivation effect of PSS on Si. Moreover, the transmission line model measurements indicate that the contact resistance (R_C) of PEDOT:PSS film and the Ag electrode is decreased for better charge collection after NHX treatment. Eventually, the best power conversion efficiency (PCE) of 13.78% for NHX-treated planar solar cells is obtained, much higher than the PCE (with best of 12.78%) of reference devices without nonpolar solvent treatment. Our results provide a facile method to tailor the vertical morphology of the PEDOT:PSS in Si/organic hybrid solar cells.

A Study of the Negligible Part Played by Dimeric Ion-Pairs under Usual Polymerization Conditions

The elementary processes occurring in the anionic polymerization of styrene with dimerically associated polystyryllithium (propagation during the anionic polymerization of dimeric polystyryllithium) in the gas phase and cyclohexane were studied using MX062X/6-31+G(d), a recently developed density functional theory (DFT) method and compared with the polymerization of styrene with non-associated polystyryllithium, which was described in a previous study. The most stable transition state in the reaction of styrene with dimeric polystyryllithium has a structure in which the side chains of styrene and the two chain end units of polystyryllithium are located in the same direction around the Li atom near the reactive site. The relative enthalpy for this transition state in cyclohexane is 28 kJ·mol⁻¹, which is much lower than that for the reaction of non-associated polystyryllithium (51 kJ·mol⁻¹). However, the relative free energy (which determines the rate constant) for the former is 93 kJ·mol⁻¹, which is greater than that for the latter by 7 kJ·mol⁻¹, indicating that the latter reaction (reaction with non-associated polystyryllithium) is advantageous over the former (reaction with dimeric polystyrylllithium). Their rates of reaction are also affected by initiator concentrations; in the case of reactions with low initiator concentrations, from which high molecular weight polymers are usually obtained, the rate of reaction corresponding to non-associated polystyryllithium is much larger than that corresponding to dimeric polystyryllithium.

Effects of ethanol storage and lipid and urea extraction on δ15 N and δ13 C isotope ratios in a benthic elasmobranch, the bluespotted maskray Neotrygon kuhlii

Ethanol storage and lipid and urea extraction had no effect on bluespotted maskray Neotrygon kuhlii muscle δ¹³ C values whereas urea-removal and ethanol storage increased δ¹⁵ N values. Results presented here show a significant δ¹⁵ N increase post-urea removal and provide additional support for this approach in future elasmobranch stable-isotope analysis (SIA) studies. Further experimental work on other elasmobranch species is needed to assess extraction and preservation effects on stable-isotope (SI) values.

New Vistas on the Anionic Polymerization of Styrene in Non-Polar Solvents by Means of Density Functional Theory

The elementary processes of anionic styrene polymerization in the gas phase and in cyclohexane were studied using M062X (a recently developed density functional theory (DFT) method) combined with the 6-31+G(d) basis sets, in order to clarify the complicated phenomena caused by the association of the active chain-ends and elucidate the details of the polymerization mechanism. Three types of HSt₂Li (a model structure of polystyryllithium chain-ends) were obtained; the well-known first structure in which Li is coordinated to the side chain, the second structure in which Li is coordinated to the phenyl ring, (both without the penultimate unit coordination), and the third structure in which Li is coordinated to both the chain-end unit and the penultimate styrene unit. Although the third HSt₂Li is the most stable as expected, the free energy for the transition state of its reaction with styrene is higher than those for the other two transition states due to its steric hindrance. The free energy for the transition state of the reaction of the second HSt₂Li with styrene is the lowest, suggesting that the route through it is the predominant reaction path. The penultimate unit effect, slower addition of styrene to HSt₂Li than to HStLi, is attributed to coordination of the penultimate styrene units of the polystyryllithium dimer (one of the starting materials) to its Li atoms. The calculated enthalpy for the reaction barrier of the second HSt₂Li with styrene in cyclohexane was found to agree with the observed apparent activation energy in benzene.