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Control of polymer aggregation by selective introduction of backbone disorder via random copolymerization has proven to be effective for optimizing the coating of fullerene-based bulk-heterojunctio...

Homocoupling defects in conjugated polymers often go undetected but may cause significant batch-to-batch variations that ultimately give seemingly identical polymers different material properties. ...

Side chain engineering has been well studied as a functional handle for controlling the properties of conjugated polymers in OSC applications, with side chain alteration typically effecting a PCE change. In this work, we highlight a unique TPD-based donor polymer system which exhibits robust photovoltaic tolerance regardless of acceptor unit side chain. While alteration of the side chain bulk from a minimally sized substituent (methyl) to a bulky substituent (cyclohexylmethyl) results in different aggregation properties of the neat polymers and the microstructures of the polymer–fullerene blends, these differences surprisingly do not translate to changes in PCE. Due to the versatility of the TPD unit for modification and the device performance invariance to side chain, this TPD-based class of polymers could serve as an excellent donor test polymer for OSC blend tuning and other applications. The findings of this work present an avenue for polymer structure and BHJ morphology manipulation without any commonly observed variations in photovoltaic performance.

In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron affinity offsets of the blended donor and acceptor often comes at the expense...

A novel family of conjugated donor-acceptor (D-A) copolymers designed with comparatively small methyl substituted acceptor units was synthesized for use as donor phase materials in bulk heterojunction (BHJ) organic photovoltaic (OPV) applications. These polymers make use of common acceptor moieties thieno [3,4-c]pyrrole-4,6-dione (TPD), diketopyrrolopyrrole (DPP), and isoindigo (iI) with methyl side chains to provide sterically unhindered sites for enhanced interactions with a molecular acceptor (MA), either PC71BM or ITIC in this study. The resulting polymers P(T4-TPD-M), P(T4-DPP-M), and P(T4-iI-M) were utilized in BHJ OPV devices where the highest performing D-A polymer, P(T4-TPD-M), obtained a maximum PCE of 7.5% with PC71BM and 4.0% with ITIC. These results indicate that minimally-sized methyl side chain derivatives of TPD, DPP, and iI can be useful acceptor moieties in D-A polymer systems, and the impact of sterics on the acceptor moiety can be elucidated in future studies through modification of the methyl side chain to bulkier aliphatic substituents.

The adoption of solution-processed active layers in the production of thin-film photovoltaics is hampered by the transition from research fabrication techniques to scalable processing. We report a detailed study of the role of processing in determining the morphology and performance of organic photovoltaic devices using a commercially available, low-solubility, high-molar mass diketopyrrolopyrrole-based polymer donor. Ambient blade coating of thick layers in an inverted architecture was performed to best model scalable processing. Device performance was strongly dependent on the introduction of either

Developing aqueous electrolyte compatible, redox-active polymers that can be processed from environmentally sustainable solvents is desirable because these traits will effectively reduce environmental impact and human health hazards during processing procedures and in the final device architecture. To achieve organic solvent solubility and aqueous compatibility, a poly(3,4-propylenedioxythiophene) containing four ester functionalities was synthesized via direct arylation polymerization. The resulting polymer was spray-cast into a thin film from the environmentally sustainable solvent 2-methyltetrahydrofuran, and the presence of multiple polar functionalities rendered the film aqueous electrolyte compatible. The multiester-functionalized polymer exhibits a relatively low onset of oxidation (∼0.4 V vs Ag/AgCl) and electrochromic character by transitioning from a colored neutral state to a colorless oxidized state with increasing potential in 0.1 M NaCl aqueous electrolyte. Additionally, the ester-functionalized polymer exhibits similar electrochromic properties in aqueous electrolytes when compared to traditional alkyl-substituted poly(3,4-propylenedioxythiophenes) in organic electrolytes, as evidenced by contrast values of ∼70% and switching speeds of ∼2 s. This work highlights the use of multipolar functionalities as a design strategy for synthesizing organic solvent processable, aqueous electrolyte compatible redox-active polymers without postpolymerization modifications or the sacrifice of electrochromic properties.

The ability to process conjugated polymers from environmentally benign solvents is essential for making organic electronics commercially viable by reducing costs and enhancing safety in the printing and processing environment. To enhance the solubility of typically alkyl-functionalized redox-active and electrochromic polymers, poly(3,4-propylenedioxythiophenes) with ester-functionalized side chains were synthesized via direct arylation polymerization, resulting in polymers that are processable from 2-methyltetrahydrofuran, ethyl acetate, and propyl acetate. Optical and atomic force microscopy results of spray-processed films indicate that topological features, such as film roughness, can be manipulated via the vapor pressure of the processing solvent. The solvent choice affects the resulting onset of absorbance and relative intensities of vibronic features, which translates into distinctly observable and quantifiable color differences. While the color is sensitive to the casting solvent, the redox prope...

Considering the facile synthesis of the cyclopentadithiophene (CPDT) building block, this study aims to synthesize and characterize two donor–acceptor type conjugated molecules, 2EH-CPDT(FBTTh2)2 and 5EN-CPDT(FBTTh2)2, with different branching points from the backbone. It was found that the branching point variation strategy slightly tunes the optical and electrochemical properties of the resulting conjugated molecule films owing to the difference between their intermolecular packing. When used as a donor material in PC71BM-based organic solar cells (OSCs), the power conversion efficiency of 2EH-CPDT(FBTTh2)2 is twice that of the ones processed using 5EN-CPDT(FBTTh2)2. Interestingly, with no post treatments, OSCs were optimized with especially low-donor content within the active layer (donor : acceptor weight ratio = 1 : 9), which allows construction of a highly transparent film with a visible transmittance over 50%, showing potential for application in integrated photovoltaics.

Three structurally disordered terpolymer derivatives of PffBT4T-2OD (PCE11), prepared by replacing a varied amount of bithiophene linkers with single thiophenes, were found to exhibit reduced aggregation in solution with increasing thiophene content, while important redox and optoelectronic properties remained similar to those of PffBT4T-2OD. Solar cells based on random terpolymer-PC71BM blends exhibited average power conversion efficiencies of over 9.5% when processed with preheated substrates, with fill factors above 70%, exceeding those from PffBT4T-2OD. Thanks to increased solubility, random terpolymer devices were able to be fabricated on room-temperature substrates, reaching virtually identical performance among all three polymers despite remarkable thicknesses of ∼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance.

We describe a homebuilt direct laser writing (DLW) system centered on a fluorescence microscope as an alternative means for the creation of microfluidic masters. Such masters are often the starting point of microanalytical platforms and are usually made using transparency masks, which are inexpensive and very convenient. However, these masks can become expensive if features are

In an effort to exploit chemistry for information science, we have constructed a system to send a message powered by a combustion reaction. Our system uses the thermal excitation of alkali metals to transmit an encoded signal over long distances. A message is transmitted by burning a methanol-soaked cotton string embedded with combinations of high, low, or zero levels of potassium, rubidium, and/or cesium ions. By measuring the intensities at the characteristic emission wavelengths of each metal in the near-infrared, 19 unique signals can be distinguished. We have built a custom telescope to detect these signals from 1 km away for nearly 10 min. The signal is isotropic, is self-powered, and has a low background. A potential application of this platform is for search and rescue signaling where another layer of information can be transmitted, in addition to the location of the beacon. This work, which seeks to encode and transmit information using chemistry instead of electronics, is part of the new field of "infochemistry".

The purpose of this experiment was to create a simple and inexpensive flame photometer to measure the concentration of sodium in beverages, such as Gatorade. We created a nebulizer using small tubing and sprayed the sample into the base of a Bunsen burner. Adjacent to the flame was a photodiode with a filter specific for the emission of the sodium D-line. After making a calibration curve, students could detect the amount of sodium in Gatorade to within 10% of the value on the label. The system costs less than $500 and can be assembled by students and used in an analytical chemistry laboratory course.

A new halochromic compound is reported with pronounced UV/Vis spectral responses that depend on the extent of protonation and on the counter-ion structure. The absorption can be controlled over the entire visible spectrum and into the near-IR via a protonation-induced assembly mechanism. Thin-films were used for colorimetric detection of acid vapors.

Fluorescence spectrometers are expensive instruments and fluorimetry is rarely used in undergraduate teaching curricula, especially in the first year. The experiment described utilizes handheld spectrometers capable of measuring absorbance and fluorescence to introduce students to drug binding to DNA. Students monitor the changes that occur in fluorescence intensity when proflavine binds to DNA in the presence and absence of sodium ions. The goals of this experiment are to illustrate principles of electronic structure, noncovalent interactions, and spectroscopic techniques. The handheld device utilized in this experiment is inexpensive and the ease of operation makes fluorescence spectroscopy accessible and exciting to first-year undergraduates.