Influence of molecular structure on the antimicrobial function of phenylenevinylene conjugated oligoelectrolytes.

Conjugated oligoelectrolytes (COEs) with phenylenevinylene (PV) repeat units are known to spontaneously intercalate into cell membranes. Twelve COEs, including seven structures reported here for the first time, were investigated for the relationship between their membrane disrupting properties and structural modifications, including the length of the PV backbone and the presence of either a tetraalkylammonium or a pyridinium ionic pendant group. Optical characteristics and interactions with cell membranes were determined using UV-Vis absorption and photoluminescence spectroscopies, and confocal microscopy. Toxicity tests on representative Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) bacteria reveal generally greater toxicity to E. faecalis than to E. coli and indicate that shorter molecules have superior antimicrobial activity. Increased antimicrobial potency was observed in three-ring COEs appended with pyridinium ionic groups but not with COEs with four or five PV repeat units. Studies with mutants having cell envelope modifications indicate a possible charge based interaction with pyridinium-appended compounds. Fluorine substitutions on COE backbones result in structures that are less toxic to E. coli, while the addition of benzothiadiazole to COE backbones has no effect on increasing antimicrobial function. A weakly membrane-intercalating COE with only two PV repeat units allowed us to determine the synthetic limitations as a result of competition between solubility in aqueous media and association with cell membranes. We describe, for the first time, the most membrane disrupting structure achievable within two homologous series of COEs and that around a critical three-ring backbone length, structural modifications have the most effect on antimicrobial activity

Using Combinatorial Inkjet Printing for Synthesis and Deposition of Metal Halide Perovskites in Wavelength‐Selective Photodetectors

Metal halide perovskites have received great attention in recent years, predominantly due to the high performance of perovskite solar cells. The versatility of the material, which allows the tunability of the bandgap, has led to its use in light-emitting diodes, photo, and X-ray detectors, among other optoelectronic device applications. Specifically in photodetectors, the tunability of the bandgap allows fabrication of spectrally selective devices. Utilizing a combinatorial inkjet printing approach, multiple perovskite compositions absorbing at specific wavelengths in a single printing step are fabricated. The drop-on-demand capabilities of inkjet printing enable the deposition of inks in a precise ratio to produce specific perovskite compositions in the printed thin film. By controlling the halide ratio in the compositions, a mixed halide gradient ranging from pure MAPbI3 via MAPbBr3 to MAPbCl3 is produced. The tunability in the absorption onset from 410 to 790 nm is demonstrated, covering the whole visible spectrum, with a precision of 8 nm steps for MAPb(BrxCl1−x)3 compositions. From this range of mixed halide perovskites, photodetectors which show spectral selectivity corresponding to the measured absorption onset are demonstrated, paving the way for use in a printed visible light spectrometer without the need for a dispersion element.Peer Reviewe

CsxFA1 xPb I1 yBry 3 Perovskite Compositions the Appearance of Wrinkled Morphology and its Impact on Solar Cell Performance

We report on the formation of wrinkle patterned surface morphologies in cesium formamidinium based CsxFA1 amp; 8722;xPb I1 amp; 8722;yBry 3 perovskite compositions with x 0 amp; 8722;0.3 and y 0 amp; 8722;0.3 under various spin coating conditions. By varying the Cs and Br contents, the perovskite precursor solution concentration and the spin coating procedure, the occurrence and characteristics of the wrinkle shaped morphology can be tailored systematically. Cs0.17FA0.83Pb I0.83Br0.17 3 perovskite layers were analyzed regarding their surface roughness, microscopic structure, local and overall composition, and optoelectronic properties. Application of these films in p amp; 8722;i amp; 8722;n perovskite solar cells PSCs with indium doped tin oxide NiOx perovskite C60 bathocu proine Cu architecture resulted in up to 15.3 and 17.0 power conversion efficiency for the flat and wrinkled morphology, respectively. Interestingly, we find slightly red shifted photoluminescence PL peaks for wrinkled areas and we are able to directly correlate surface topography with PL peak mapping. This is attributed to differences in the local grain size, whereas there is no indication for compositional demixing in the films. We show that the perovskite composition, crystallization kinetics, and layer thickness strongly influence the formation of wrinkles which is proposed to be related to the release of compressive strain during perovskite crystallization. Our work helps us to better understand film formation and to further improve the efficiency of PSCs with widely used mixed perovskite composition

Exploring the Precursor Process Property Space in Metal Halide Perovskite Thin Films

Die Anpassung der Bandlücke und die Herstellung mittels lösungsbasierter Prozesse charakterisieren Metallhalogenid Perowskite. Sie sind vielversprechend für die Anwendung in optoelektronischen Bauteilen, die die Abscheidung von hochwertigen Dünnschichten erfordern. Deren Qualität hängt stark vom Kristallisationsverhalten ab, welches durch die Komposition der Lösung bestimmt ist. Ziel dieser Arbeit ist es, Korrelationen im Präkursor Prozess Eigenschaftsraum von Metallhalogenid Perowskit zu bewerten und Formierungsprozesse zu rationalisieren. Phasenreinheit, Morphologie und Absorptionseigenschaften zeichnen die Qualität der Perowskit Dünnschichten aus. Die Optimierung der Herstellung von hochwertigen Filmen über einen breiten Bandlückenbereich wird zuerst beleuchtet. Die Rationalisierung der Formierungsprozesse erweist sich als fundamental, um reproduzierbare Präparationsroutinen für hochwertige Filme zu entwickeln. Anschlie end wird ein optischer in situ Aufbau zur Rationalisierung von Formierungsprozessen vorgestellt. Abhängig vom Halogenidverhältnis in der MAPb IxBr1 x 3 Reihe werden verschiedene Formierungswege eingeschlagen. Während sich das reine Bromid direkt und Iodid reiche Perowskite über die intermediäre Solvatphase MA 2 DMSO 2Pb3I8 bilden, bilden sich gemischte Halogenide zwischen 0.1 amp; 8804; x amp; 8804; 0.6 über beide Wege. Die Formierung über konkurrierende Wege erklärt die kompositorische Heterogenität der gemischten Halogenidproben. Zuletzt werden Formierungsprozesse von Bromid Perowskiten rationalisiert und Abhängigkeiten der Kinetik von der Lösungskonzentration zeigen sich. Niedrige Konzentrationen führen zu einer beschleunigten Kristallisation und Schichtdickenabnahme des Nassfilms. Dieser Trend wird durch geringere Kolloidwechselwirkungen und niedriger koordinierte Blei Bromid Komplexe in verdünnten Lösungen erklärt. Die Korrelation im Präkursor Prozess Eigenschaftsraum hebt die Herstellung von Perowskiten aus chemischer Sicht zu einem nicht trivialen Prozess

Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination: A Quantitative Comparison of Experimental Observations and Thermodynamic Models

Photo- and charge-carrier induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase- segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge-carriers trigger the process but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena we investigate the full compositional range of methylammonium lead bromide/iodide samples, MAPb(Br$_x$I$_{1-x}$)$_3$ with $x = 0\ldots 1$, by simultaneous in-situ X-ray diffraction and photoluminescence spectroscopy during illumination. The quantitative comparison of composition-dependent in-situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation can be rationalized with the previously established thermodynamic models. However, we observe a progression of the phase-segregation that can only be rationalized by considering long-lived accumulative photo-induced material alterations. We suggest that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase-segregation and anticipate our findings to provide crucial insight for the development of more sophisticated models

Photoinduced phase segregation and degradation of perovskites revealed by x-ray photoelectron spectroscopy

Pb-based perovskite absorbers with organic (i.e., CH3NH3+) and inorganic (i.e., Cs+) cations and a halide composition of 75% Br and 25% I are investigated with x-ray photoelectron spectroscopy while submitted to environmental stress factors to study their stability. Changes in chemical properties of the absorbers were monitored in ultra-high vacuum and under simulated solar, as well as, x-ray irradiation. Although changes are detected for both types of perovskite absorbers, the organic cation perovskite exhibits a more pronounced tendency to photodegrade

Multi-Stage Phase-Segregation of Mixed Halide Perovskites under Illumination : A Quantitative Comparison of Experimental Observations and Thermodynamic Models

Photo- and charge-carrier-induced ion migration is a major challenge when utilizing metal halide perovskite semiconductors for optoelectronic applications. For mixed iodide/bromide perovskites, the compositional instability due to light- or electrical bias induced phase-segregation restricts the exploitation of the entire bandgap range. Previous experimental and theoretical work suggests that excited states or charge carriers trigger the process, but the exact mechanism is still under debate. To identify the mechanism and cause of light-induced phase-segregation phenomena, the full compositional range of methylammonium lead bromide/iodide samples are investigated, MAPb(BrxI1-x)3 with x = 0…1, by simultaneous in situ X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy during illumination. The quantitative comparison of composition-dependent in situ XRD and PL shows that at excitation densities of 1 sun, only the initial stage of photo-segregation is rationalized with the previously established thermodynamic models. However, a progression of the phase segregation is observed that is rationalized by considering long-lived accumulative photo-induced material alterations. It is suggested that (additional) photo-induced defects, possibly halide vacancies and interstitials, need to be considered to fully rationalize light-induced phase segregation and anticipate the findings to provide crucial insight for the development of more sophisticated models

Using Combinatorial Inkjet Printing for Synthesis and Deposition of Metal Halide Perovskites in Wavelength-Selective Photodetectors

Metal halide perovskites have received great attention in recent years, predominantly due to the high performance of perovskite solar cells. The versatility of the material, which allows the tunability of the bandgap, has led to its use in light-emitting diodes, photo, and X-ray detectors, among other optoelectronic device applications. Specifically in photodetectors, the tunability of the bandgap allows fabrication of spectrally selective devices. Utilizing a combinatorial inkjet printing approach, multiple perovskite compositions absorbing at specific wavelengths in a single printing step are fabricated. The drop-on-demand capabilities of inkjet printing enable the deposition of inks in a precise ratio to produce specific perovskite compositions in the printed thin film. By controlling the halide ratio in the compositions, a mixed halide gradient ranging from pure MAPbI3 via MAPbBr3 to MAPbCl3 is produced. The tunability in the absorption onset from 410 to 790 nm is demonstrated, covering the whole visible spectrum, with a precision of 8 nm steps for MAPb(BrxCl1−x)3 compositions. From this range of mixed halide perovskites, photodetectors which show spectral selectivity corresponding to the measured absorption onset are demonstrated, paving the way for use in a printed visible light spectrometer without the need for a dispersion element