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An innovative process consisting of Fe(II)-dosed anaerobic bioreactors and an oxidizing basin was used to continuously treat a synthetic wastewater (COD/sulfate mass ratio 2:1 and Fe/S molar ratio 1:1). Sludge recycling effects were evaluated on ten occasions, in which anaerobic sludge was collected, biochemically oxidized with mechanical aeration in the oxidizing basin before being mixed with the wastewater influent. The sludge recycling resulted in better effluent quality compared to the baseline operation without recycling. More Fe and S were retained as sludge in the bioreactors with sludge recycling (Fe 94%, S 91%) than those when the bioreactors were operated without sludge recycling (Fe 76%, S 86%). Scanning electron microscopic analysis showed that bacterial cells and iron sulfide intermixed in the anaerobic sludge and the presence of microbial exopolymeric substances. X-ray spectroscopic analyses showed amorphous FeS formed from the dosed ferrous iron and biogenic bisulfide, and suggested long-term conversion of the amorphous FeS to more stable crystalline FeS and FeS2 in the anaerobic bioreactors. In the oxidizing basin, oxidation of iron sulfides was of both chemical and biological nature, and their oxidized forms including amorphous FeO/Fe2O3 mixture and partially/fully oxidized sulfurs. Experimental results also indicated amorphous FeS was more readily oxidized than FeS2. Phylogenetic analysis revealed microorganisms related to Desulfomonile tiedjei (sulfur reducing) and Alkaliphilus metalliredigens (iron reducing) in the anaerobic bioreactors, and Thiobacter subterraneus (sulfur oxidizing) and Rubrivivax gelatinosus (iron oxidizing) related microorganisms in the oxidizing basin.

Summary In contrast to conventional colloidal quantum dots (CQDs), management of insulating ligands on perovskite CQDs is challenging because their ionic bonds are highly vulnerable to polar solvents. Consequently, there have been only a few examples of perovskite CQD solar cells incorporating relatively robust inorganic perovskite of which optoelectronic properties are not ideal for photovoltaic devices. Here, we report efficient and stable CQD solar cells based on formamidinium lead triiodide (FAPbI3) CQDs realized by rational surface regulation. Tailoring polarity of antisolvents for the post-synthetic process enabled effective removal of the insulating ligands on FAPbI3 CQDs while preserving perovskite cores. Owing to the enhanced inter-dot electrical coupling, a power-conversion efficiency of 8.38% was demonstrated. Furthermore, the FAPbI3 CQDs-based devices showed superior stability over those of bulk FAPbI3 devices. Thermodynamic and crystallographic analyses revealed that enhanced contribution of the surface energy and lattice contraction contribute to their superior stability.

The Lewis acid–base adduct approach has been widely used to form uniform perovskite films, which has provided a methodological base for the development of high-performance perovskite solar cells. However, its incompatibility with formamidinium (FA)-based perovskites has impeded further enhancement of photovoltaic performance and stability. Here, we report an efficient and reproducible method to fabricate highly uniform FAPbI3 films via the adduct approach. Replacement of the typical Lewis base dimethyl sulfoxide (DMSO) with N-methyl-2-pyrrolidone (NMP) enabled the formation of a stable intermediate adduct phase, which can be converted into a uniform and pinhole-free FAPbI3 film. Infrared and computational analyses revealed a stronger interaction between NMP with the FA cation than DMSO, which facilitates the formation of a stable FAI·PbI2·NMP adduct. On the basis of the molecular interactions with different Lewis bases, we proposed criteria for selecting the Lewis bases. Owed to the high film quality, per...

Anomalous current–voltage (J–V) hysteresis in perovskite (PSK) solar cell is open to dispute, where hysteresis is argued to be due to electrode polarization, dipolar polarization, and/or native defects. However, a correlation between those factors and J–V hysteresis is hard to be directly evaluated because they usually coexist and are significantly varied depending on morphology and crystallinity of the PSK layer, selective contacts, and device architecture. In this study, without changing morphology and crystallinity of PSK layer in a planar heterojunction structure employing FA0.9Cs0.1PbI3, a correlation between J–V hysteresis and trap density is directly evaluated by means of thermally induced PbI2 regulating trap density. Increase in thermal annealing time at a given temperature of 150 °C induces growth of PbI2 on the PSK grain surface, which results in significant reduction of nonradiative recombination. Hysteresis index is reduced from 0.384 to 0.146 as the annealing time is increased from 5 to 100 ...

We report our results of developing perovskite thin films with high coverage, improved uniformity and preserved crystalline continuity in a single pass deposition. This approach, inspired by the natural phenomena of tears of wine, works by regulating the hydrodynamics of the material comprising of droplets during spray-pyrolysis. In contrast to conventional spray-pyrolysis where droplets dry independently and form a rough morphology, the use of binary solvent system creates localized surface tension gradients that initiate Marangoni flows, thus directing the incoming droplets to spontaneously undergo coalescing, merging and spreading into a continuous wet films before drying. By systematically exploring the dynamics of spreading and drying, we achieve spray-coated perovskite photovoltaics with power conversion efficiency of 14.2%, a near two-fold improvement than that of the spray-pyrolysis counterpart. Of particular significance is the fact that the single pass deposition technique unveils novel inroads in efficient management of lead consumption during deposition.

Effects of Fe(III)/sulfate (Fe/S) ratio on organic carbon oxidation kinetics and microbial ecology of a novel Fe(III)-dosed anaerobic wastewater treatment system were investigated in this study. Fixed-film batch bioreactors under three Fe/S molar ratios (1, 2, and 3) yielded COD oxidation rates that increased with the Fe/S ratio, and estimated Michaelis-Menten model parameters Vmax ranging in 0.47–1.09 mg/L⋅min and Km in 2503-3267 mg/L. Both iron and sulfate reducing bacteria contributed to the organics oxidation, and the produced sludge materials contained both biomass (32–45 wt.%) and inorganic precipitates from biogenic ferrous iron and sulfide (68-55 wt.%). Spectroscopic and chemical elemental analyses indicated that the inorganic fraction of the sludge materials contained both FeS and FeS2, and had Fe/S stoichiometric ratios close to 1. Microbiological analyses of the biofilm samples revealed that the major putative iron- and sulfate reducers were Geobacter sp. and Desulfovibrio sp. along with noticeable N-fixing and fermentative bacteria. The COD oxidation rate had a positive correlation with the relative abundance of iron reducers, and both increased with the Fe/S ratio. A conceptual framework was proposed to illustrate the effects of Fe/S ratio on organics oxidation rate, microbial ecology and their interplays.

Deterioration models for pavement surface distresses have been developed using probabilistic modelling approaches. The condition data is collected using visual inspection surveys. Distress data used in the modelling include cracking, texture loss and stone loss of different pavement surfacing types. The latter includes dense graded asphalt, open graded asphalt, ultra-thin asphalt, sprayed/chip seal and geotextile seal (chip seal with geotextile underlay). Probabilistic modelling approaches used include logistic regression and Markov chains (MC). The two variables used in the modelling are distress rating and surface age. These models are to be used for network level management. For the network modelled herein, logistic models are found to provide predictions that are comparable with actual average condition data at different age values. It is also observed that predictions of most MC models are higher than predictions of logistic models and actual average data.

Reported in this paper are the process and outcomes of deterioration modelling for five types of pavement bituminous surfacing for use in identifying and prioritising resurfacing needs. Surface condition data is collected using subjective assessment surveys and the condition ratings of distresses are combined into a single measure referred to as surface inspection rating (SIR). Deterioration models of SIR as a function of surface age are developed for the five networks using three modelling approaches. They include regression analysis, logistic regression analysis and Markov chains. A comparison between the output models of the three approaches is presented and assessed in terms of predictions reasonableness and accuracy considering their closeness to actual data and practical local experience and engineering judgement. Overall the findings indicate that the three modelling approaches provide similar predictions and deterioration rates for most surfacing types. A comparison of performance between the five...

We have developed an electrospraying technique inspired from Marangoni flow seen in nature. We demonstrate our ability to synthesise highly crystalline uniform perovskite thin films with enhanced coverage and high absorption. Due to a difference in the vapour pressure of DMSO and NMP, a gradient force is developed that helps in propagating the incoming precursor droplet to coalesce and merge with other droplets thus inducing a dynamic self-assembly within the thin film. This results in thin films with high uniformity and good morphological and topological characteristics, that collectivelty resulted in a respectable PCE of greater than 14%. Optical studies are conducted in parallel to better understand the energy phase space of perovskite crystals. The high temperature tetragonal phase showed a high recombination rate of 180 ns, ideal for photovoltaic performances, while the low temperature measurements reveal considerable complexity in spectral and dynamic properties that demand further invesgtiation.

Y.-C.C. and A.-Y.L. contributed equally to this work. V.T. gratefully acknowledges the research award from the Doctoral New Investigator Award from ACS Petroleum Fund (ACS PRF 54717-DNI10, V.T.). Characterization and fabrication of HER electrodes in this work were performed as User Proposals (#4240) at the Molecular Foundry, Lawrence Berkeley National Lab, supported by the Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Raman spectroscopy was performed at the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. Y.C. acknowledges the fellowship support from National Aeronautics and Space Administration (NASA) grant no. NNX15AQ01. Work at Sandia, including experimental design, materials synthesis, microscopy, were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. Equipment at Sandia were furnished with support from the Laboratory Directed Research and Development programs. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. A.Y.L, X.Y., and L.J.L. acknowledge the support from KAUST. V.T. is indebted to Dr. Hidetaka Ishihara, Xuan Wei, Jose Hernandez, Teresa L. Chen, and Vipawee Limsakoune, for the fruitful discussion in droplet dynamics and assistance in instrumentation.

The halide perovskite (PVSK) materials (with ABX3 formulation) have emerged as “dream materials” for photovoltaic (PV) applications due to their remarkable physical properties such as high optical absorption coefficient, carrier mobility, long carrier diffusion lengths, etc. These properties have enabled the PV devices to reach higher than 20% power conversion efficiencies (PCE) in record time. The further pursuit of higher PCE and improved stability brings forth increasing interests in so-called “mixed composition” PVSK materials, consisting of partial substitution of the A, B, and/or X-sites with alternative elements/molecules of similar size. Herein, we highlight the recent advances in developing mixed PVSK for PVs and their relevant optoelectronic properties. We mainly focus on mixed PVSK materials in the form of polycrystalline thin films, but also discuss nanostructured and two-dimensional (2D) PVSK materials due to the increasing interest of broad readership. Efforts are exerted to elucidate the design principles of mixed PVSK and fabrication techniques for high performance optoelectronic devices, which help deepen our fundamental understanding of mixed PVSK systems. We hope this review will shed light onto the design and synthesis of mixed PVSK materials to further the progress of PVSK photovoltaics towards higher efficiencies and longer lifetimes.

Organic–inorganic perovskites that combine the strength of both chemical worlds have emerged as tantalizing candidates for next generation photovoltaics. Here, the electrohydrodynamically assisted continuous liquid interface propagation as a general, and potentially scalable nanomanufacturing route toward synthesizing high quality perovskite thin films in a rapid and high throughput fashion is reported. This strategy conceptually mimics the advantageous self-organizing features of emulsion droplets where the use of a binary solvent system, concurrently and continuously, initiates a three-stage process of coalescence, spreading, and merging, thus optimizing thin film morphology upon deposition without the needs for additional engineering steps. The resulting perovskite thin film not only exhibits a smooth topology with the root mean square roughness of only a few nm but also reveals hybrid morphology where micrometer-sized grains intersperse between interconnected and continuous crystalline networks. This gives rise to the highest power conversion efficiency of 16.50% and average 14.68%; representing a nearly twofold increase compared to that of conventional spray-pyrolysis approach. As a final critical aspect, the proposed strategy contributes new insights to efficiently managing the environmentally hazardous lead during processing, significantly reducing the amount by two orders of magnitude compared to that of spin-coating to achieve the same thin film thickness.