Spectral dependence of the internal quantum efficiency of organic solar cells: effect of charge generation pathways.

The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:PC70BM and PCPDTBT:PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes.

Partially Neutralized Polyacrylic Acid as an Efficient Binder for Aqueous Ceramic-Coated Separators for Lithium-Ion Batteries.

A partially neutralized polyacrylic acid (Pn-PAA) is used for coating sub-micron-sized α-alumina on a conventional microporous polyolefin separator, fabricating a ceramic-coated separator (CCS). Pn-PAA acts as a dispersant and binder by adsorbing itself on alpha(α)-alumina surfaces under acidic condition through the columbic interaction, providing a repulsive force to disperse fine alumina in aqueous suspension, and binds alumina strongly on plasma-treated separator through hydrogen bonding. This CCS shows favorable wettability in carbonate-based liquid electrolyte and ionic conduction due to the high hydrophilicity of Pn-PAA and alumina. With that, this study found that Pn-PAA-made-CCS yields a substantial adhesion strength of ~106 N/m with enhanced cycle stability, a specific capacity of 145.0 mAh/g after 200 cycles at 1 C at room temperature in half cells (LFP/Li metal).

Catalytic asymmetric [4+2] annulation initiated by an aza-Rauhut-Currier reaction: facile entry to highly functionalized tetrahydropyridines.

Under control: The first example of chiral amino phosphine catalysts for the title reaction between vinyl ketones and N-sulfonyl-1-aza-1,3-dienes has been developed. Under ambient conditions, this protocol provides straightforward access to densely functionalized, enantioenriched tetrahydropyridines with high levels of sterecontrol in good to excellent yields.

Effects of Chemical Composition, Film Thickness, and Morphology on the Electrochromic Properties of Donor-Acceptor Conjugated Copolymers Based on Diketopyrrolopyrrole.

A series of diketopyrrolopyrrole (DPP) and propylenedioxythiophene (ProDOT)-containing random copolymers with different donor-to-acceptor ratios is synthesized through Stille coupling polymerizations. The low-bandgap polymers display dark tones with colors ranging from magenta to blue, and reveal reversible colored-to-transmissive electrochromism in absorption/transmission-type devices with high optical contrasts (up to 48 and 77 % in the visible and near-infrared regions, respectively), modest switching speeds (a few to tens of seconds) and coloration efficiencies (267-574 cm2 C-1 ), as well as good long-term ambient redox stabilities. The structure-performance relationship of the polymers, in particular, the role of donor-to-acceptor ratio, is investigated, and it is shown that an increase in the amount of acceptor in the polymers leads to slower oxidative but faster reductive switching, accompanied with enhancement of the redox stability. In addition, further study on the influence of film thickness and film morphology reveals that devices with higher optical contrasts are attainable from thicker polymer films at the expense of switching speeds; films with high uniformity and connectedness together with open, loose structures at submicron to micron scale are favorable for achieving good electrochromic performance.

Catalytic asymmetric formal [4 + 1] annulation leading to optically active cis-isoxazoline N-oxides.

The catalytic asymmetric synthesis of densely functionalized cis-isoxazoline N-oxides was realized with novel use of an organocatalyst, (S)-2-(azidodiphenylmethyl)pyrrolidine (4e) (Tan, B.; Zhu, D.; Zhang, L.; Chua, P. J.; Zeng, X.; Zhong, G. Chem.-Eur. J. 2010, 16, 3842; Olivares-Romero, J. L.; Juaristi, E. Tetrahedron 2008, 64, 9992), via an elegant formal [4 + 1] annulation strategy using readily available 2-nitroacrylates and α-iodoaldehydes.

Synthesis and biological activity evaluation of 1,2,3-thiadiazole derivatives as potential elicitors with highly systemic acquired resistance.

Elicitors provide a broad spectrum of systemic acquired resistance by altering the physical and physiological status of the host plants and, therefore, are among the most successful directions in modern pesticide development for plant protection. To develop a novel elicitor with highly systemic acquired resistance, two series of thiazole- and oxadiazole-containing thiadiazole derivatives were rationally designed and synthesized according to the principle of combination of bioactive substructures in this work. Their structures were characterized by (1)H nuclear magnetic resonance (NMR), infrared (IR), high-resolution mass spectrometry (HRMS), or elemental analysis. Their potential systemic acquired resistance as an elicitor was also evaluated; bioassay results indicated that, among the 23 compounds synthesized, three compounds, 10a, 10d, and 12b, displayed better systemic acquired resistance than the positive control, tiadinil, a commercialized 1,2,3-thiadiazole-based elicitor. In addition, three other compounds, 10f, 12c, and 12j, exhibited a certain degree of fungus growth inhibition in vitro or in vivo. Our results demonstrated that, in combination of bioactive substructures is an interesting exploration for novel pesticide development, thiazole- and oxadiazole-containing thiadiazole derivatives are potential elicitors with good systemic acquired resistance.

Control of four stereocenters in an organocatalytic domino double Michael reaction: efficient synthesis of multisubstituted cyclopentanes.

A highly enantioselective and diastereoselective domino organocatalytic double Michael reaction which provides expedited access to multifunctionalized five-membered rings catalyzed by 9-amino-9-deoxyepiquinine (V) has been developed. Simple operational procedures, high yields (81-92%), excellent enantioselectivity (90-97% ee), diastereoselectivities (95:5->99:1 dr), and immense potential of synthetic versatility of the products render this new methodology highly appealing for asymmetric synthesis.