RESUMEN
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 o-dichlorobenzene (DCB), 1,8-diiodooctane, or diphenyl ether cosolvent into the chloroform (CHCl3) solution, which were all shown to drastically improve the morphology. To understand the origin of these morphological changes as a result of the addition of the cosolvent, in situ studies with grazing-incidence X-ray scattering and optical reflection interferometry were performed. Use of any of the cosolvents decreases the domain size relative to the single solvent system and moved the drying mechanism away from what is likely liquid-liquid phase separation to solid-liquid phase separation driven by polymer aggregation. Comparing the CHCl3 + DCB cast films to the CHCl3-only cast films, we observed both the formation of small domains and an increase in crystallinity during the evaporation of DCB due to a high nucleation rate from supersaturation. This resulted in percolated bulk heterojunction networks that performed similarly well with a wide range of film thicknesses from 180 to 440 nm, making this system amenable to continuous roll-to-roll processing methods.
RESUMEN
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 â¼400 nm. Thus, we show that the random terpolymer approach is successful in improving processability while maintaining device performance.
RESUMEN
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 (â¼0.4 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 â¼70% and switching speeds of â¼2 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.
RESUMEN
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.
RESUMEN
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".