Jeremy A. Cody

Contribution of Aggregate States and Energetic Disorder to a Squaraine System Targeted for Organic Photovoltaic Devices

Squaraine dyes have significant potential for use in organic photovoltaic devices because their chemical and packing structure tunability leads to a broad solid state panchromaticity. Nevertheless, broadening of the spectrum does not always give rise to increasing power conversion efficiencies. Furthermore, the same processing strategy used to make devices from different squaraines does not lead to the same optimized performance. In this work, by varying the environmental conditions of a set of anilinic squaraines, we demonstrate that spin-cast thin films are made up of a complex set of states, with each state contributing differently to the overall device efficiency. We demonstrate crystallochromy in that small changes in the packing structure give rise to dramatically different absorption spectra. Through a remarkable comparison between squaraines in poly(methyl methacrylate) solid solution and squaraine:PC60BM blends, we also show long-range and orientational disorder broadening, which distorts the ability to correlate qualitative spectroscopic assessment with an understanding of the device mechanism. We conclude that a full quantitative assessment of the populations of each excited state must be carried out in order to make progress toward an improved understanding of each states contribution to charge transfer at the bulk heterojunction interface.

UV-Stressed Daphnia pulex Increase Fitness through Uptake of Vitamin D3.

Ultraviolet radiation is known to be highly variable in aquatic ecosystems. It has been suggested that UV-exposed organisms may demonstrate enough phenotypic plasticity to maintain the relative fitness of natural populations. Our long-term objective is to determine the potential photoprotective effect of vitamin D3 on Daphnia pulex exposed to acute or chronic UV radiation. Herein we report our initial findings in this endeavor. D. pulex survival and reproduction (fitness) was monitored for 5 d as a proof of concept study. Significantly higher fitness was observed in the D. pulex with D3 than those without (most extreme effects observed were 0% survival in the absence of D3 and 100% with 10 ppm D3). Vitamin D3 was isolated from the culture media, the algal food (Pseudokirchneriella), and the D. pulex and quantified using high performance liquid chromatography (HPLC). Vitamin D3 was fluorescently labeled using a phenothiazinium dye and added to cultures of D. pulex. Images demonstrating the uptake of D3 into the tissues and carapace of the D. pulex were acquired. Our initial findings suggest a positive role for D3 in ecosystems as both UV-stressed algae and Daphnia sequester D3, and D. pulex demonstrate increased fitness in the presence of D3.

Influence of squaraine aggregation on short-circuit current and device efficiency

Linear absorption measurements, current-voltage characteristics, and time-resolved microwave conductivity measurements were utilized to investigate the impact of molecular aggregation of a novel donor material on photovoltaic device efficiency. We report efficiencies of 2.4+/-0.3% and explain the increase in short-circuit current and efficiency as a function of the increased aggregation.

Ritter Reactions between Alcohols and Acetonitrile Mediated by the Conducting Polymer Poly-(3,4-ethylenedioxy Thiophene) (PEDOT)

Abstract Herein, we report new reactivity of the conducting polymer, poly-(3,4-ethylenedioxy thiophene) (PEDOT), where PEDOT mediates a Ritter reaction between alcohols and acetonitrile. The yields were variable and in most cases competitive with results obtained using sulfuric acid. Attempts at a stoichiometric reaction between benzonitrile and diphenylmethanol are also reported herein. Finally, described here are preliminary mechanistic studies that suggest PEDOT is behaving as an alcohol-selective or specific Lewis acid. Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for full experimental and spectral details. GRAPHICAL ABSTRACT

Transforming the Organic Chemistry Lab Experience: Design, Implementation, and Evaluation of Reformed Experimental Activities—REActivities

Reformed experimental activities (REActivities) are an innovative approach to the delivery of the traditional material in an undergraduate organic chemistry laboratory. A description of the design and implementation of REActivities at both a four- and two-year institution is discussed. The results obtained using a reformed teaching observational protocol are described and correlated to the transferability of REActivities between different instructors and their transportability between different institutions.

Theory and assignment of intermolecular charge transfer states in squaraines and their impact on efficiency in bulk heterojunction solar cells (Presentation Recording)

Squaraines are targeted for organic photovoltaic devices because of their high extinction coefficients over a broad wavelength range from visible to near infra-red (NIR). Moreover, their side groups can be changed with profound effects upon their ability to crystallize, leading to improvements in charge mobility and exciton diffusion. The broadening in squaraine absorption is often qualitatively attributed to H- and J-aggregates based on the exciton model, proposed by Kasha. However, such assignment is misleading considering that spectral shifts can arise from sources other than excitonic coupling. Our group has shown that packing structure influences the rate of charge transfer; thus a complete and accurate reassessment of the excited states must be completed before the true charge transfer mechanism can be confirmed. In this work, we will show how squaraine H-aggregates can pack in complete vertical stacks or slipped vertical stacks depending upon sidegroups and processing conditions. Hence, we uncover the contribution of an intermolecular charge transfer (IMCT) state through essential states modeling validated by spectroscopic and X-Ray diffraction data. We further show external quantum efficiency data that describe the influence of the IMCT state on the efficiency of our devices. This comprehensive understanding of squaraine aggregates drives the development of more efficient organic photovoltaic devices, leading towards a prescription for derivatives that can be tailored for optimized exciton diffusion, charge transfer, higher mobilities and reduced recombination in small molecule OPV devices.

Explaining the molecular structure of the bulk heterojunction with simple electronic measurements and marcus-hush theory for squaraine: PCBM organic photovoltaic devices

A unique donor material for small molecule organic solar cells is shown to be opto-electrically tunable with thermal annealing. The system is characterized and shown to make working devices (PCE=1.1 +/- 0.3%). Examination of the spectral response of the devices before and after thermal annealing show an interesting decrease in spectral response that is explained by examining both the material properties and through application of Marcus-Hush theory. The proposed explanation could lay the groundwork for a predictive model to analyze potential device candidates.

A study of squaraine small molecule donor materials for application in organic photovoltaics

A unique donor material for small molecule organic solar cells is shown to be opto-electrically tunable with thermal annealing. The system is characterized and shown to make working devices (PCE=1.1 +/- 0.3%). Examination of the spectral response of the devices before and after thermal annealing show an interesting decrease in spectral response that is explained by examining both the material properties and through application of Marcus-Hush theory. The proposed explanation could lay the groundwork for a predictive model to analyze potential device candidates.