Anna K. Hailey

Bi2S3 nanowire networks as electron acceptor layers in solution-processed hybrid solar cells

We report the assembly of Bi2S3 into percolated networks. Subsequent infiltration of poly(3-hexylthiophene), P3HT, as the electron donor generates an inorganic–organic active layer. Inverted solar cells fabricated with these active layers exhibit power-conversion efficiencies as high as 3.3%. To the best of our knowledge, this is the first example of a hybrid solar cell comprising a percolated network of single-crystalline Bi2S3 nanowires and P3HT.

Isoindigo-Containing Molecular Semiconductors: Effect of Backbone Extension on Molecular Organization and Organic Solar Cell Performance

We have synthesized three new isoindigo-based small molecules by extending the conjugated length through the incorporation of octyl-thiophene units between the isoindigo core and benzothiophene terminal units. Both UV–vis and Grazing incidence X-ray diffraction experiments show that such extension of the π-conjugated backbone can induce H-aggregation, and enhance crystallinity and molecular ordering of these isoindigo-based small molecules in the solid state. Compared to two other isoindigo-based derivatives in the series, the derivative with two octyl-thiophene units, BT-T2-ID, is the most crystalline and ordered, and its molecular packing motif appears to be substantially different. Devices utilizing these new extended isoindigo-based small molecules as the electron donor exhibit higher performance than those utilizing nonextended BT-ID as the electron donor. Particularly, devices containing BT-T2-ID in an as-cast blend with PC61BM show power conversion efficiencies up to 3.4%, which is comparable to the best devices containing isoindigo-based molecular semiconductors and is a record among devices containing isoindigo-based small molecules that were processed in the absence of any additives.

The Diffraction Pattern Calculator (DPC) toolkit: a user-friendly approach to unit-cell lattice parameter identification of two-dimensional grazing-incidence wide-angle X-ray scattering data.

The DPC toolkit is a simple-to-use computational tool that helps users identify the unit-cell lattice parameters of a crystal structure that are consistent with a set of two-dimensional grazing-incidence wide-angle X-ray scattering data. The input data requirements are minimal and easy to assemble from data sets collected with any position-sensitive detector, and the user is required to make as few initial assumptions about the crystal structure as possible. By selecting manual or automatic modes of operation, the user can either visually match the positions of the experimental and calculated reflections by individually tuning the unit-cell parameters or have the program perform this process for them. Examples that demonstrate the utility of this program include determining the lattice parameters of a polymorph of a fluorinated contorted hexabenzocoronene in a blind test and refining the lattice parameters of the thin-film phase of 5,11-bis(triethylsilylethynyl)anthradithiophene with the unit-cell dimensions of its bulk crystal structure being the initial inputs.

The effect of regioisomerism on the crystal packing and device performance of desymmetrized anthradithiophenes

Anthradithiophenes (ADTs) are typically synthesized as inseparable mixtures of regioisomers. In this paper, we describe the synthesis of desymmetrized anthradithiophenes containing one trialkylsilylethyne solubilizing group, which allowed chromatographic separation of the three resulting isomers. Cyclic voltammograms, as well as absorption and emission spectra for all isomers, were nearly identical. However, X-ray crystallography revealed that the positions of the sulfur atoms in each isomer strongly influence crystal packing, corroborating calculations that show the S–π interaction to be less stabilizing than the C–H–π interaction. Isomer 3c packs in a pseudo 1-D fashion while isomers 3a and 3b pack as isolated π-stacked pairs. Isomer 3c shows a field-effect mobility four orders of magnitude higher than isomers 3a and 3b, presumably due to this difference in packing motif.

Understanding the Crystal Packing and Organic Thin-Film Transistor Performance in Isomeric Guest–Host Systems

In order to understand how additives influence the structure and electrical properties of active layers in thin-film devices, a compositionally identical but structurally different guest-host system based on the syn and anti isomers of triethylsilylethynyl anthradithiophene (TES ADT) is systematically explored. The mobility of organic thin-film transistors (OTFTs) comprising anti TES ADT drops with the addition of only 0.01% of the syn isomer and is pinned at the mobility of OTFTs having pure syn isomer after the addition of only 10% of the isomer. As the syn isomer fraction increases, intermolecular repulsion increases, resulting in a decrease in the unit-cell density and concomitant disordering of the charge-transport pathway. This molecular disorder leads to an increase in charge trapping, causing the mobility of OTFTs to drop with increasing syn-isomer concentration. Since charge transport is sensitive to even minute fractions of molecular disorder, this work emphasizes the importance of prioritizing structural compatibility when choosing material pairs for guest-host systems.

Capillary effects in guided crystallization of organic thin films

Recently, it has been demonstrated that solvent-vapor-induced crystallization of triethylsilylethynyl anthradithiophene (TES ADT) thin films can be directed on millimeter length scales along arbitrary paths by controlling local crystal growth rates via pre-patterning the substrate. Here, we study the influence of capillary effects on crystallization along such channels. We first derive an analytical expression for the steady-state growth front velocity as a function of channel width and validate it with numerical simulations. Then, using data from TES ADT guided crystallization experiments, we extract a characteristic channel width, which provides the smallest feature size that can be obtained by this technique.

CCDC 1481034: Experimental Crystal Structure Determination

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