Andrew D. Scully

Inactivation of Food‐borne Spoilage and Pathogenic Micro‐organisms on the Surface of a Photoactive Polymer

The photodynamic action of a novel photoactive polymer comprising covalently bound anthraquinone (AQ) moieties was evaluated after developing a methodology to reliably immobilize viable micro‐organisms onto polymer film surfaces. The survival of Escherichia coli, Bacillus cereus (vegetative cells and spores), Fusarium oxysporum and Saccharomyces cerevisiae microbes inoculated on the surface of inert polymeric substrates was assessed to determine the effect of inoculum composition, drying rate and exposure to ultraviolet (UV‐A) radiation. Their survival was highly dependent on microbial genus, with E. coli consistently displaying markedly shorter survival times than the other microbes, and B. cereus spores being the most resistant. Inoculation of the microbes onto the surface of the photoactive polymer films, followed by exposure to UV‐A radiation, dramatically accelerated the inactivation of all microbial types studied compared with their survival on the surface of inert polymer substrates. Simultaneous exposure to both oxygen and UV‐A radiation is required to affect cell survival, which is consistent with this effect most likely originating from the photoinduced production of singlet oxygen by the photoactive polymer. These results provide further compelling evidence that singlet oxygen produced exogenously by this photoactive polymeric substrate can successfully inactivate a broad spectrum of microbes on the substrate’s surface.

Aggregation of a dibenzo[b,def]chrysene based organic photovoltaic material in solution.

Detailed electrochemical studies have been undertaken on molecular aggregation of the organic semiconductor 7,14-bis((triisopropylsilyl)-ethynyl)dibenzo[b,def]chrysene (TIPS-DBC), which is used as an electron donor material in organic solar cells. Intermolecular association of neutral TIPS-DBC molecules was established by using (1)H NMR spectroscopy as well as by the pronounced dependence of the color of TIPS-DBC solutions on concentration. Diffusion limited current data provided by near steady-state voltammetry also reveal aggregation. Furthermore, variation of concentration produces large changes in shapes of transient DC and Fourier transformed AC (FTAC) voltammograms for oxidation of TIPS-DBC in dichloromethane. Subtle effects of molecular aggregation on the reduction of TIPS-DBC are also revealed by the highly sensitive FTAC voltammetric method. Simulations of FTAC voltammetric data provide estimates of the kinetic and thermodynamic parameters associated with oxidation and reduction of TIPS-DBC. Significantly, aggregation of TIPS-DBC facilitates both one-electron oxidation and reduction by shifting the reversible potentials to less and more positive values, respectively. EPR spectroscopy is used to establish the identity of one-electron oxidized and reduced forms of TIPS-DBC. Implications of molecular aggregation on the HOMO energy level in solution are considered with respect to efficiency of organic photovoltaic devices utilizing TIPS-DBC as an electron donor material.

Directing nucleation and growth kinetics in solution-processed hybrid perovskite thin-films

A heightened understanding of nucleation and growth mechanisms is paramount if effective solution processing of organic-inorganic perovskite thin-films for optoelectronic applications is to be achieved. Many fabrication techniques have been utilized previously to develop high-performance perovskite layers but there remains an absence of a unifying model that describes accurately the formation of these materials from solution. The present study provides a thorough analysis of nucleation and growth kinetics underpinning the development of hybrid organic-inorganic perovskite thin-films. Through precise control of the perovskite growth conditions the spacing of heterogeneous nucleation sites was varied successfully from several hundred nanometers to several hundred microns. The crystalline regions surrounding these nuclei were found to comprise clusters of highly-oriented crystal domains exceeding 100 μm in diameter. However, no beneficial correlation was found between the size of these well-oriented grain-clusters and the optoelectronic performance. The formation of the perovskite microstructure features characteristics of both classical and non-classical growth mechanisms. The insights into perovskite thin-film growth developed by the present study provide clear implications for the development of future hybrid perovskite microstructures.摘要如何利用溶液法制备高质量、高效率的有机-无机杂化钙钛矿薄膜光电器件, 取决于对该体系的核化和晶体生长机理的深入研究.尽管用很多方法可以制备出高性能的钙钛矿薄膜, 到目前为止, 还缺乏一个准确且统一的模型, 去解释钙钛矿晶体是如何从溶液中析出生长的过程. 本文通过对晶体核化和生长动力学的详细研究, 提出了有机-无机杂化钙钛矿薄膜材料的形成机制. 通过精准控制钙钛矿晶粒生长的条件, 异质晶核之间的距离能够在几百纳米到几百微米之间调控. 我们还发现在晶核周围直径超过100微米范围, 聚集着取向高度一致的晶体团簇. 但是这些晶体团簇的尺寸大小, 与提高钙钛矿光电器件的性能并没有什么直接的对应关系; 钙钛矿材料微观结构的形成机理,兼有经典和非经典晶体生长的特征. 因此对钙钛矿薄膜生长的深入研究, 将有助于进一步控制杂化钙钛矿薄膜的微观结构.

Photocatalytic and Chemoselective Transfer Hydrogenation of Diarylimines in Batch and Continuous Flow

A visible-light photocalytic method for the chemoselective transfer hydrogenation of imines in batch and continuous flow is described. The reaction utilizes Et3N as both hydrogen source and single-electron donor, enabling the selective reduction of imines derived from diarylketimines containing other reducible functional groups including nitriles, halides, esters, and ketones. The dual role of Et3N was confirmed by fluorescence quenching measurements, transient absorption spectroscopy, and deuterium-labeling studies. Continuous-flow processing facilitates straightforward scale-up of the reaction.

An Alternating Donor–Acceptor Conjugated Polymer Based on Benzodithiophene and [3,4-c]pyrrole-4,6-dione: Synthesis, Characterization, and Application in Photovoltaic Devices

The synthesis is described of a new alternating donor–acceptor semiconducting polymer based on an N-octylthieno[3,4-c]pyrrole-4,6-dione building block together with a newly designed 2,3-bis(2-ethylhexyl)thiophenylethynyl substituted benzodithiophene (BDT). The introduction of electron-rich thiophene units to BDT raises the highest occupied molecular orbital (HOMO) level of the conjugated polymer and the concomitant reduction of the bandgap enhances the harvesting of solar radiation. This modification also introduces less sterically demanding triple bonds, thereby potentially enabling more favourable molecular interactions and an extra dimension of conjugation perpendicular to the main polymer chain. The optoelectronic properties of this new conjugated polymer were evaluated using UV-visible absorption and fluorescence spectroscopy, photoelectron spectroscopy in air, photo-induced charge extraction by linearly increasing voltage (Photo-CELIV), and density functional theory calculations. The polymer absorbs broadly in the wavelength range 300–700 nm in solution and the solid state. The estimated HOMO and LUMO levels of −5.4 and −3.6 eV, respectively, correspond to a bandgap of 1.8 eV. Photovoltaic devices fabricated using the polymer as the active layer displayed power conversion efficiencies (PCEs) of up to 1 %. Photo-CELIV results provide evidence that rapid recombination and poor charge mobility are likely contributing factors to the relatively low PCE values observed.

Interfacial benzenethiol modification facilitates charge transfer and improves stability of cm-sized metal halide perovskite solar cells with up to 20% efficiency

Metal halide perovskite solar cells (PSC) exhibit outstanding power conversion efficiencies when fabricated as mm-sized devices, but creation of high-performing large-area PSCs that are stable under operating conditions on a sufficiently long timescale still presents a significant challenge. We demonstrate herein that modification of the interface between the perovskite and a spiro-OMeTAD hole-transporting material with commercially available para-substituted benzenethiol molecules facilitates fabrication of cm-sized PSCs with both improved efficiency and stability. Comprehensive analysis using specialised and conventional physical characterisation techniques has been undertaken to demonstrate that band alignment at the perovskite surface can be tuned to improve the solar cell efficiency via adsorption of benzenethiols with a significant dipole moment. Moreover, modification of the perovskite with cyano-substituted benzenethiol enhances charge extraction and reduces charge recombination in the devices. These effects enable improvements in the power conversion efficiency of PSCs from 19.0 to 20.2% and from 18.5 to 19.6% under 1 sun AM 1.5G irradiation with 0.16 and 1.00 cm2 apertures, respectively. Most importantly, benzenethiol-modified perovskite solar cells retain more than 80% of the initial performance after 185 h of continuous operation at 50% relative humidity and 50 °C device temperature under 1 sun irradiation, while devices with no interfacial modification undergo continuous deterioration down to 35% of the initial efficiency. These significant improvements are provided by a very simple and highly reproducibile modification procedure that can be readily adopted in other types of PSCs.