Studies of recombination in organic and hybrid solar cells using electroluminescence

The performance of solution processed solar cells such as organic bulk heterojunction (OPV) devices is limited by strong recombination. However, the mechanisms are still unclear. In this thesis, I develop a toolbox using steady-state spectroscopy measurements to explore the recombination mechanisms in a range of solution-processed solar cells. In the first results chapter, I use the reciprocity relation between light absorption and light emission to explore theoretical and practical performance limits for solar cells based on organic semiconductors and perovskites and compare the results with data for state-of-the-art photovoltaic cells made from GaAs, c-Si, and CIGS. In OPV systems, I show that the energetic losses due to the mismatch of the bandgap have been significantly reduced through optimisation of the donor polymer, but the non-radiative recombination losses remain the same and become the major barrier to higher performance. In the next two chapters, I use light intensity dependence of open-circuit voltage measurement (suns-VOC) and electroluminescence – injection current measurement (EL-J) to disentangle recombination mechanisms in OPV and perovskite cells, respectively. First, I identify the present of Shockley-Read-Hall recombination and surface recombination in OPV devices. I intentionally control the sample geometry to modulate the amount of surface recombination and demonstrate that surface recombination can significantly affect the device performance. In the following chapter, I analyse time dependent suns-VOC and EL-J measurements on perovskite cells with different architectures and pre-conditioning regimes used. I identify the changes in recombination mechanisms with delay time and pre-conditions. The effects of ion migration are used to interpret the results. In the final chapter, I apply luminescence spectroscopy techniques to investigate the degree of fullerene crystallinity in polymer:fullerene blends. Charge-transfer state emission is used to probe the onset of the crystallisation of fullerenes in an amorphous polymer. I relate the CT peak shift directly to the change in microstructure of a blend film.Open Acces

RpoN (σ54) Is Required for Floc Formation but Not for Extracellular Polysaccharide Biosynthesis in a Floc-Forming Aquincola tertiaricarbonis Strain.

Some bacteria are capable of forming flocs, in which bacterial cells become self-flocculated by secreted extracellular polysaccharides and other biopolymers. The floc-forming bacteria play a central role in activated sludge, which has been widely utilized for the treatment of municipal sewage and industrial wastewater. Here, we use a floc-forming bacterium, Aquincolatertiaricarbonis RN12, as a model to explore the biosynthesis of extracellular polysaccharides and the regulation of floc formation. A large gene cluster for exopolysaccharide biosynthesis and a gene encoding the alternative sigma factor RpoN1, one of the four paralogues, have been identified in floc formation-deficient mutants generated by transposon mutagenesis, and the gene functions have been further confirmed by genetic complementation analyses. Interestingly, the biosynthesis of exopolysaccharides remained in the rpoN1-disrupted flocculation-defective mutants, but most of the exopolysaccharides were secreted and released rather than bound to the cells. Furthermore, the expression of exopolysaccharide biosynthesis genes seemed not to be regulated by RpoN1. Taken together, our results indicate that RpoN1 may play a role in regulating the expression of a certain gene(s) involved in the self-flocculation of bacterial cells but not in the biosynthesis and secretion of exopolysaccharides required for floc formation.IMPORTANCE Floc formation confers bacterial resistance to predation of protozoa and plays a central role in the widely used activated sludge process. In this study, we not only identified a large gene cluster for biosynthesis of extracellular polysaccharides but also identified four rpoN paralogues, one of which (rpoN1) is required for floc formation in A. tertiaricarbonis RN12. In addition, this RpoN sigma factor regulates the transcription of genes involved in biofilm formation and swarming motility, as previously shown in other bacteria. However, this RpoN paralogue is not required for the biosynthesis of exopolysaccharides, which are released and dissolved into culture broth by the rpoN1 mutant rather than remaining tightly bound to cells, as observed during the flocculation of the wild-type strain. These results indicate that floc formation is a regulated complex process, and other yet-to-be identified RpoN1-dependent factors are involved in self-flocculation of bacterial cells via exopolysaccharides and/or other biopolymers

Experimental and theoretical optical properties of methylammonium lead halide perovskites

The optical constants from the ellipsometry of single crystals of CH3NH3PbX3(X = I, Br, Cl) are interpreted with high levelab initioQSGW calculations.</p

Identifying Dominant Recombination Mechanisms in Perovskite Solar Cells by Measuring the Transient Ideality Factor

The light ideality factor determined by measuring the open-circuit voltage (V) as a function of light intensity is often used to identify the dominant recombination mechanism in solar cells. Applying this “Suns-V” technique to perovskite cells is problematic since the V evolves with time in a way that depends on the previously applied bias (V), bias light intensity, device architecture and processing route. Here, we show that the dominant recombination mechanism in two structurally similar CH3NH3PbI3 devices containing either mesoporous Al2O3 or TiO2 layers can be identified from the signature of the transient ideality factor following application of a forward bias, V, to the device in the dark. The transient ideality factor is measured by monitoring the evolution of V as a function of time at different light intensities. The initial values of ideality found using this technique are consistent with estimates of the ideality factor obtained from measurements of photoluminescence vs light intensity and electroluminescence vs current density. Time-dependent simulations of the measurement on modeled devices, which include the effects of mobile ionic charge, reveal that this initial value can be correlated to an existing zero-dimensional model while steady-state values must be analyzed taking into account the homogeneity of carrier populations throughout the absorber layer. The analysis shows that Shockley-Read-Hall (SRH) recombination through deep traps at the charge-collection interfaces is dominant in both architectures of measured device. Using transient photovoltage measurements directly following illumination on bifacial devices, we further show that the perovskite–electron-transport-layer interface extends throughout the mesoporous TiO2 layer, consistent with a transient ideality signature corresponding to SRH recombination in the bulk of the film. This method will be useful for identifying performance bottlenecks in alternative variants of perovskite and other mixed ionic-electronic conducting absorber-based solar cells

Alternative strategies of nutrient acquisition and energy conservation map to the biogeography of marine ammonia-oxidizing archaea

Ammonia-oxidizing archaea (AOA) are among the most abundant and ubiquitous microorganisms in the ocean, exerting primary control on nitrification and nitrogen oxides emission. Although united by a common physiology of chemoautotrophic growth on ammonia, a corresponding high genomic and habitat variability suggests tremendous adaptive capacity. Here, we compared 44 diverse AOA genomes, 37 from species cultivated from samples collected across diverse geographic locations and seven assembled from metagenomic sequences from the mesopelagic to hadopelagic zones of the deep ocean. Comparative analysis identified seven major marine AOA genotypic groups having gene content correlated with their distinctive biogeographies. Phosphorus and ammonia availabilities as well as hydrostatic pressure were identified as selective forces driving marine AOA genotypic and gene content variability in different oceanic regions. Notably, AOA methylphosphonate biosynthetic genes span diverse oceanic provinces, reinforcing their importance for methane production in the ocean. Together, our combined comparative physiological, genomic, and metagenomic analyses provide a comprehensive view of the biogeography of globally abundant AOA and their adaptive radiation into a vast range of marine and terrestrial habitats

The Thermoanaerobacter Glycobiome Reveals Mechanisms of Pentose and Hexose Co-Utilization in Bacteria

Author Summary Renewable liquid fuels derived from lignocellulosic biomass could alleviate global energy shortage and climate change. Cellulose and hemicellulose are the main components of lignocellulosic biomass. Therefore, the ability to simultaneously utilize pentose and hexose (i.e., co-utilization) has been a crucial challenge for industrial microbes producing lignocellulosic biofuels. Certain thermoanaerobic bacteria demonstrate this unusual talent, but the genetic foundation and molecular mechanism of this process remain unknown. In this study, we reconstructed the structure and dynamics of the first genome-wide carbon utilization network of thermoanaerobes. This transcriptome-based co-expression network reveals that glucose, xylose, fructose, and cellobiose catabolism are each featured on distinct functional modules. Furthermore, the dynamics of the network suggests a distinct yet collaborative nature between glucose and xylose catabolism. In addition, we experimentally demonstrated that these novel network-derived features can be rationally exploited for product-yield enhancement via optimized timing and balanced loading of the carbon supply in a substrate-specific manner. Thus, the newly discovered modular and precisely regulated network elucidates unique features of thermoanaerobic glycobiomes and reveals novel perturbation strategies and targets for the enhanced thermophilic production of lignocellulosic biofuels.Yeshttp://www.plosgenetics.org/static/editorial#pee

Function Synthesis Algorithm of RTD-Based Universal Threshold Logic Gate

The resonant tunneling device (RTD) has attracted much attention because of its unique negative differential resistance characteristic and its functional versatility and is more suitable for implementing the threshold logic gate. The universal logic gate has become an important unit circuit of digital circuit design because of its powerful logic function, while the threshold logic gate is a suitable unit to design the universal logic gate, but the function synthesis algorithm for the n-variable logical function implemented by the RTD-based universal logic gate (UTLG) is relatively deficient. In this paper, three-variable threshold functions are divided into four categories; based on the Reed-Muller expansion, two categories of these are analyzed, and a new decomposition algorithm of the three-variable nonthreshold functions is proposed. The proposed algorithm is simple and the decomposition results can be obtained by looking up the decomposition table. Then, based on the Reed-Muller algebraic system, the arbitrary n-variable function can be decomposed into three-variable functions, and a function synthesis algorithm for the n-variable logical function implemented by UTLG and XOR2 is proposed, which is a simple programmable implementation

Effect of regionalized structures on rock fracture process

Abstract The structure of rocks plays a crucial role in their failure process. However, it is ignored that the interactions between rock internal structure and the effect of its own evolution on the rock fracture process. To investigate the effect between the evolution law of rock regionalized structures and their interaction relationships during failure. We conducted an experiment using visual acoustic imaging monitoring to study rock failure, introducing a new concept of characteristics of rock structure—regionalized structures. The findings reveal three main types of regionalized structures in rocks: skeleton regions, variable regions, and damage regions. These structures combine to form four categories of complex rock structures: block-type support skeletons, point column-type support skeletons, suspension-type weak support skeletons, and no skeletons. During the failure process, we found that these regionalized structures worked together synergistically to control rock failure. Although the evolutionary relationships among the structures show some similarities, the final fracture states vary significantly. Stress and strain distribution patterns clearly demonstrate that variations in the force capacities and roles of the regionalized structures influence the synergistic evolutionary relationships, ultimately impacting the mode of rock failure. This work provides new insights for further research on rock failure mechanisms and can significantly contribute to preventing rock engineering disasters related to regionalized structures

The Effect of IL-8 on Collagen Synthesis in Corneal Fibroblasts

IL-8 is highly expressed in tears of keratoconus patients, but its mechanism is still unclear. Abnormal collagen synthesis and degradation are one of the pathogenesis of keratoconus. In this study, the effect of IL-8 on collagen synthesis in corneal fibroblasts and its molecular mechanism were discussed to provide reference for clarifying the pathogenesis of keratoconus. siRNA interference system was established and the expression of IL-8 in corneal fibroblasts was silenced by siRNA. The expression changes of genes related to collagen synthesis and degradation as well as other pro-inflammatory factors after IL-8 silence were analyzed by real-time fluorescent quantitative PCR. The content of total collagen and the activity of MMP-2 were detected by ELISA and gelatin zymography, respectively. Western blot was used to analyze the expression changes of the key proteins of related signal pathway. The results show that the total collagen content and the expression of collagen synthesis genes (COL1A2, COL3A1, COL5A3 and COL6A1) increased significantly after IL-8 silencing, while the expression and activity of MMP-2 which participated in collagen degradation decreased. In addition, silencing IL-8 reduced the gene expression of IL-6, IL-1β, and VEGFA/VEGFR2, as well as the protein expression of AKT and ERK1/2 in downstream signal pathway. IL-8 regulated the expression of VEGF and other pro-inflammatory factors. It negatively regulated the collagen synthesis and participated in MMP-2 mediated collagen degradation in corneal fibroblasts through PI3K/AKT and ERK signaling pathways