Opaque Cells Research Articles

Quantitative loss analysis of opaque perovskite solar cells using transient and steady-state characterization

Quantitative loss analysis of opaque perovskite solar cells using transient and steady-state characterization

The Vps21 signalling pathway regulates white-opaque switching and mating in Candida albicans

ABSTRACT Candida albicans is able to switch between two epigenetic cell types, namely white and opaque. Multiple conserved signalling pathways control the switch between white and opaque cell types in response to environmental changes. Here, we report the regulatory roles of the endosomal Rab family GTPase Vps21 and associated key components of the Vps21 signalling pathway in white-opaque switching and mating in C. albicans. Deletion of VPS21 promoted a switch from the white to the opaque phenotype in the presence of N-acetyl-glucosamine (GlcNAc). Consistently, inactivation of the guanine nucleotide exchange factor of Vps21 (Vps9) and downstream components in the Vps21 pathway (Vps3, Vac1, and Pep12) had similar promoting effects on phenotypic switching. The mating efficiency of opaque cells is much higher than that of white cells under standard laboratory culture conditions. However, compared to the wildtype strain, the vps21/vps21, vps9/vps9, vps3/vps3, vac1/vac1, and pep12/pep12 mutant strains exhibited dramatically reduced mating efficiencies. Quantitative RT-PCR assays demonstrated that inactivation of the Vps21 signalling pathway led to downregulation of pheromone expression and mating response pathway associated genes. Taken together, our findings indicate that the conserved Vps21 signalling pathway plays critical roles in the regulation of cell-type switching and mating in C. albicans.

Ligand Homogenized Br-I Wide-Bandgap Perovskites for Efficient NiOx-Based Inverted Semitransparent and Tandem Solar Cells.

Phase heterogeneity of bromine-iodine (Br-I) mixed wide-bandgap (WBG) perovskites has detrimental effects on solar cell performance and stability. Here, we report a heterointerface anchoring strategy to homogenize the Br-I distribution and mitigate the segregation of Br-rich WBG-perovskite phases. We find that methoxy-substituted phenyl ethylammonium (x-MeOPEA+) ligands not only contribute to the crystal growth with vertical orientation but also promote halide homogenization and defect passivation near the buried perovskite/hole transport layer (HTL) interface as well as reduce trap-mediated recombination. Based on improvements in WBG-perovskite homogeneity and heterointerface contacts, NiOx-based opaque WBG-perovskite solar cells (WBG-PSCs) achieved impressive open-circuit voltage (Voc) and fill factor (FF) values of 1.22 V and 83%, respectively. Moreover, semitransparent WBG-PSCs exhibit a PCE of 18.5% (15.4% for the IZO front side) and a high FF of 80.7% (79.4% for the IZO front side) for a designated illumination area (da) of 0.12 cm2. Such a strategy further enables 24.3%-efficient two-terminal perovskite/silicon (double-polished) tandem solar cells (da of 1.159 cm2) with a high Voc of over 1.90 V. The tandem devices also show high operational stability over 1000 h during T90 lifetime measurements.

Optical design and bandgap engineering in ultrathin multiple quantum well solar cell featuring photonic nanocavity

AbstractUltrathin solar cells are efficient and captivating devices with unique technological and scientific features in terms of minimal material consumption, fast fabrication processes, and good compatibility with semi‐transparent applications. Such photovoltaic (PV) technologies can enable effective synergy between optical and electronic confinements with large tuning capabilities of all the optoelectronic characteristics. In this work, the implications of the optical design and the bandgap engineering in ultrathin hydrogenated amorphous Si/Ge multiple quantum well (MQW) solar cells featuring photonic nanocavity are analyzed based on experimental measurements and optoelectronic modelling. By changing the period thicknesses and the positions of QWs inside the deep‐subwavelength nanophotonic resonator, the spatial and spectral distributions of the optical field and the local absorption are strongly affected. This leads to a modulation of the absorption resonance condition, the absorption edge and the resulting photocurrent outputs. Because of quantum confinement effect, the change of MQW configurations with different individual QW periods while keeping similar total thickness of about 20 nm alters both the bandgap energy and the band offset at the QW/barrier heterojunctions. This in turn controls the photovoltage as well as the carrier collection efficiency in solar cells. The highest open circuit voltage and fill factor values are achieved by employing MQW device configuration with 2.5 nm‐thin QWs. A record efficiency above 5.5% is reached for such emerging ultrathin Si/Ge MQW solar cell technology using thinner QWs with sufficient number, because of the optimum trade‐off between all the optoelectronic characteristic outputs. The presented design rules for opaque ultrathin solar cells with quantum‐confined nanostructures integrated in a photonic nanocavity can be generalized for the engineering of relevant multifunctional semitransparent PV devices.

White-opaque switching in Candida albicans: cell biology, regulation, and function.

SUMMARYCandida albicans remains a major fungal pathogen colonizing humans and opportunistically invading tissue when conditions are predisposing. Part of the success of C. albicans was attributed to its capacity to form hyphae that facilitate tissue invasion. However, in 1987, a second developmental program was discovered, the "white-opaque transition," a high-frequency reversible switching system that impacted most aspects of the physiology, cell architecture, virulence, and gene expression of C. albicans. For the 15 years following the discovery of white-opaque switching, its role in the biology of C. albicans remained elusive. Then in 2002, it was discovered that in order to mate, C. albicans had to switch from white to opaque, a unique step in a yeast mating program. In 2006, three laboratories simultaneously identified a putative master switch gene, which led to a major quest to elucidate the underlying mechanisms that regulate white-opaque switching. Here, the evolving discoveries related to this complicated phenotypic transition are reviewed in a quasi-chronological order not only to provide a historical perspective but also to highlight several unique characteristics of white-opaque switching, which are fascinating and may be important to the life history and virulence of this persistent pathogen. Many of these characteristics have not been fully investigated, in many cases, leaving intriguing questions unresolved. Some of these include the function of unique channeled pimples on the opaque cell wall, the capacity to form opaque cells in the absence of the master switch gene WOR1, the formation of separate "pathogenic" and "sexual" biofilms, and the possibility that a significant portion of natural strains colonizing the lower gastrointestinal tract may be in the opaque phase. This review addresses many of these characteristics with the intent of engendering interest in resolving questions that remain unanswered.

Physiological adventures in Candida albicans: farnesol and ubiquinones.

SUMMARYFarnesol was first identified as a quorum-sensing molecule, which blocked the yeast to hyphal transition in Candida albicans, 22 years ago. However, its interactions with Candida biology are surprisingly complex. Exogenous (secreted or supplied) farnesol can also act as a virulence factor during pathogenesis and as a fungicidal agent triggering apoptosis in other competing fungi. Farnesol synthesis is turned off both during anaerobic growth and in opaque cells. Distinctly different cellular responses are observed as exogenous farnesol levels are increased from 0.1 to 100 µM. Reported changes include altered morphology, stress response, pathogenicity, antibiotic sensitivity/resistance, and even cell lysis. Throughout, there has been a dearth of mechanisms associated with these observations, in part due to the absence of accurate measurement of intracellular farnesol levels (Fi). This obstacle has recently been overcome, and the above phenomena can now be viewed in terms of changing Fi levels and the percentage of farnesol secreted. Critically, two aspects of isoprenoid metabolism present in higher organisms are absent in C. albicans and likely in other yeasts. These are pathways for farnesol salvage (converting farnesol to farnesyl pyrophosphate) and farnesylcysteine cleavage, a necessary step in the turnover of farnesylated proteins. Together, these developments suggest a unifying model, whereby high, threshold levels of Fi regulate which target proteins are farnesylated or the extent to which they are farnesylated. Thus, we suggest that the diversity of cellular responses to farnesol reflects the diversity of the proteins that are or are not farnesylated.

Strain background of Candida albicans interacts with SIR2 to alter phenotypic switching.

The genetic background between strains of a single species and within a single strain lineage can significantly impact the expression of biological traits. This genetic variation may also reshape epigenetic mechanisms of cell identity and environmental responses that are controlled by interconnected transcriptional networks and chromatin-modifying enzymes. Histone deacetylases, including sirtuins, are critical regulators of chromatin state and have been directly implicated in governing the phenotypic transition between the 'sterile' white state and the mating-competent opaque state in Candida albicans, a common fungal commensal and pathogen of humans. Here, we found that a previously ambiguous role for the sirtuin SIR2 in C. albicans phenotypic switching is likely linked to the genetic background of mutant strains produced in the RM lineage of SC5314. SIR2 mutants in a specific lineage of BWP17 displayed increased frequencies of switching to the opaque state compared to the wild-type. Loss of SIR2 in other SC5314-derived backgrounds, including newly constructed BWP17 sir2Δ/Δ mutants, failed to recapitulate the increased white-opaque switching frequencies observed in the original BWP17 sir2Δ/Δ mutant background. Whole-genome sequencing revealed the presence of multiple imbalanced chromosomes and large loss of heterozygosity tracts that likely interact with SIR2 to increase phenotypic switching in this BWP17 sir2Δ/Δ mutant lineage. These genomic changes are not found in other SC5314-derived sir2Δ/Δ mutants that do not display increased opaque cell formation. Thus, complex karyotypes can emerge during strain construction that modify mutant phenotypes and highlight the importance of validating strain background when interpreting phenotypes.

Four‐Terminal Tandem Based on a PM6:L8‐BO Transparent Solar Cell and a 7 nm Ag Layer Intermediate Electrode

To overcome transmission and thermalization losses from single‐junction solar cells, the two‐terminal tandem cell configuration is one of the most widely followed approaches. Unfortunately, the need to match the current from both cells, in addition to the fabrication of an interlayer with excellent optical and electronic performances, makes such two‐terminal configurations a challenging approach. Herein, the fabrication of a four‐terminal tandem incorporating a front transparent cell made using a 7 nm Ag back electrode and a PM6:L8‐BO blend which exhibits a bandgap close to the optimal according to the detailed balance theory is reported. For the opaque back cell in such tandem, a PTB7‐Th:O6T‐4F blend is used. A 16.94% power conversion efficiency is achieved when such two cells are configured in a four‐terminal device separated by a WO3/LiF/WO3 multilayer providing an optimal light absorption distribution among the two cells.

Luminous Transmittance and Color Rendering Characteristics of Evaporated Chalcopyrite Thin Films for Semitransparent Photovoltaics

The luminous transmittance and the color rendering index of daylight through semitransparent photovoltaic glazing are essential parameters for visual comfort indoors, and they must be considered for different absorber materials that were traditionally developed for opaque solar cells, such as those of the chalcopyrite type. With this aim, various chalcopyrite compounds (CuInSe2, CuInS2 and CuGaS2) were prepared by means of evaporation and then measured to obtain their optical absorption spectra. These experimental data are used here to calculate the solar absorptance (αS), luminous transmittance (τL) and color rendering index (Ra) as a function of the chalcopyrite film thickness. The comparative analysis of the different factors indicates that 70 nm thick CuInSe2 is optimal to guarantee excellent visual comfort (τL = 50% and Ra = 93%) while absorbing as much solar irradiance (αS = 37%) as 130 nm thick CuInS2 or 900 nm thick CuGaS2. The second option (130 nm thick CuInS2) is also considered good (τL = 40% and Ra = 80%), but for CuGaS2, the thickness should be kept below 250 nm in order to obtain a suitable color rendering Ra ≥ 60%.

Structure and interactions of prion-like domains in transcription factor Efg1 phase separation

Candida albicans, a prominent member of the human microbiome, can make an opportunistic switch from commensal coexistence to pathogenicity accompanied by an epigenetic shift between the white and opaque cell states. This transcriptional switch is under precise regulation by a set of transcription factors (TFs), with Enhanced Filamentous Growth Protein 1 (Efg1) playing a central role. Previous research has emphasized the importance of Efg1’s prion-like domain (PrLD) and the protein’s ability to undergo phase separation for the white-to-opaque transition of C. albicans. However, the underlying molecular mechanisms of Efg1 phase separation have remained underexplored. In this study, we delved into the biophysical basis of Efg1 phase separation, revealing the significant contribution of both N-terminal (N) and C-terminal (C) PrLDs. Through NMR structural analysis, we found that Efg1 N-PrLD and C-PrLD are mostly disordered but have prominent partial α-helical secondary structures in both domains. NMR titration experiments suggest that the partially helical structures in N-PrLD act as hubs for self-interaction as well as Efg1 interaction with RNA. Using condensed-phase NMR spectroscopy, we uncovered diverse amino acid interactions underlying Efg1 phase separation. Particularly, we highlight the indispensable role of tyrosine residues within the transient α-helical structures of PrLDs particularly in the N-PrLD compared to the C-PrLD in stabilizing phase separation. Our study provides evidence that the transient α-helical structure is present in the phase-separated state and highlights the particular importance of aromatic residues within these structures for phase separation. Together, these results enhance the understanding of C. albicans transcription factor interactions that lead to virulence and provide a crucial foundation for potential antifungal therapies targeting the transcriptional switch.

The transcription factor Ofi1 is critical for white-opaque switching in natural MTLa/α isolates of Candida albicans.

Candida albicans, an opportunistic fungal pathogen, is able to switch between two distinct cell types: white and opaque. While white-to-opaque switching is typically repressed by the a1/α2 heterodimer in MTLa/α cells, it was recently reported that switching can also occur in some natural MTLa/α strains under certain environmental conditions. However, the regulatory program governing white-opaque switching in MTLa/α cells is not fully understood. Here, we collected 90 clinical isolates of C. albicans, 16 of which possess the ability to form opaque colonies. Among the known regulators implicated in white-opaque switching, only OFI1 exhibited significantly higher expression in these 16 strains compared to the reference strain SC5314. Importantly, ectopic expression of OFI1 in both clinical isolates and laboratory strains promoted switching frequency even in the absence of N-acetylglucosamine and high CO2 , the optimal condition for white-to-opaque switching in MTLa/α strains. Deleting OFI1 resulted in a reduction in opaque-formation frequency and the stability of the opaque cell in MTLa/α cells. Ofi1 binds to the promoters of WOR1 and WOR3 to induce their expression, which facilitates white-to-opaque switching. Ofi1 is conserved across the CTG species. Altogether, our study reported the identification of a transcription factor Ofi1 as the critical regulator that promotes white-to-opaque switching in natural MTLa/α isolates of C. albicans.

Interfacial modification engineering for efficient and stable MA-free wide-bandgap perovskite solar cells by grain regrowth

Introducing GuSCN reduces the defect density of perovskites by one order of magnitude. Consequently, an MA-free opaque wide-bandgap perovskite solar cell achieves 20.92% power conversion efficiency with excellent stability.

Envisioning the future: optically transparent metasurface-based solar thermophotovoltaic with high conversion efficiency

Transparent solar thermo-photovoltaic (TPV) technology combines visible transparency and solar energy conversion. They are developed for their potential applications in buildings and vehicles windows, where conventional opaque solar cells may not be feasible. TPV’s offer a promising solution to harness solar energy without compromising aesthetics or functionality of transparent surfaces. Broadband absorption at UV and IR frequencies and simultaneous transmission at visible frequencies can be achieved by fabricating metamaterials that employ semi-conducting oxides. In this study, an optically transparent metasurface (OTM) based STPV composed of indium tin oxide (ITO) is introduced as the transparent metal and ZnS as a substrate layer. Our design offers a cost-effective and scalable solution for large-scale fabrication. The designed OTM structure exhibits exceptional absorption capabilities, achieving an absorption rate of up to 99% in the UV region. Additionally, it achieves over 90% absorptivity in the far infrared range and maintains a high average transmittance at visible frequencies. Furthermore, the absorption remains consistently high, exceeding 90%, even when the incident angle is less than 70° for both TE and TM polarization waves. This innovative design holds promise for various applications requiring high-performance transparent metasurface absorbers/emitters. The proposed transparent metasurface based STPV holds great potential for efficient utilization in combined solar/thermal conversion systems.

Recognizing Hand Gestures Using Solar Cells

We design a system, SolarGest, which can recognize hand gestures near a solar-powered device by analyzing the patterns of the photocurrent. SolarGest is based on the observation that each gesture interferes with incident light rays on the solar panel in a unique way, leaving its discernible signature in harvested photocurrent. Using solar energy harvesting laws, we develop a model to optimize design and usage of SolarGest. To further improve the robustness of SolarGest under non-deterministic operating conditions, we combine dynamic time warping with Z-score transformation in a signal processing pipeline to pre-process each gesture waveform before it is analyzed for classification. We evaluate SolarGest with both conventional opaque solar cells as well as emerging see-through transparent cells. Our experiments demonstrate that SolarGest achieves 99% for six gestures with a single cell and 95%for fifteen gesture with a22solar cell array. The power measurement study suggests that SolarGest consume 44% less power compared to light sensor based systems.

Opaque Cell Specific Proteome of Candida albicans ATCC 10231.

Candida albicans, a polymorphic opportunistic pathogen of humans, can exist in different morphological forms like yeast, hyphae, pseudohyphae, chlamydospores and white and opaque cells. Proteomic analysis of opaque form of C. albicans ATCC 10231 is carried out in the present study using micro-LC-MS/MS and validated using expression analysis of selected genes using RT-qPCR and mitochondrial membrane potential (MMP) assay. This is the first report identifying opaque cell-specific proteins of C. albicans. A total of 188 proteins were significantly modulated under opaque form compared to white cells, of which 110 were up-regulated, and 78 were down-regulated. It was observed that oxidative phosphorylation (OxPhos) and oxidative stress are enhanced in C. albicans cells growing under opaque form as proteins involved in OxPhos (Atp1, Atp3, Atp16, Atp7, Cox6, Nuc2, Qcr7 and Sdh12) and oxidative stress response (Gcs1, Gtt11, Gpx2, Sod1, Ccp1 and Lys7) were significantly up-regulated. The maximum up-regulation of 23.16 and 13.93-fold is observed in the case of Ccp1 and Nuc2, respectively. The down-regulation of proteins viz. Als1, Csh1, Sap9 and Rho1 determining cell surface chemistry indicates modulation in cell wall integrity and reduced adhesion of opaque cells compared to white cells. This study is significant as it is the first draft of the proteomic profile of opaque cells that suggests enhanced OxPhos, oxidative stress, and modulation in cell surface chemistry that indicates reduced adhesion and cell wall integrity that could be associated with reduced virulence in opaque form. However, a deeper investigation is needed to explore it further.

Cell-type memory in a single-cell eukaryote requires the continuous presence of a specific transcription regulator

A fundamental question in biology is how a eukaryotic cell type can be stably maintained through many rounds of DNA replication and cell division. In this paper, we investigate this question in a fungal species, Candida albicans, where two different cells types (white and opaque) arise from the same genome. Once formed, each cell type is stable for thousands of generations. Here, we investigate the mechanisms underlying opaque cell "memory." Using an auxin-mediated degradation system, we rapidly removed Wor1, the primary transcription activator of the opaque state and, using a variety of methods, determined how long cells can maintain the opaque state. Within approximately 1 h of Wor1 destruction, opaque cells irreversibly lose their memory and switch to the white cell state. This observation rules out several competing models for cell memory and demonstrates that the continuous presence of Wor1 is needed to maintain the opaque cell state-even across a single cell division cycle. We also provide evidence for a threshold concentration of Wor1 in opaque cells, below which opaque cells irreversibly switch to white cells. Finally, we provide a detailed description of the gene expression changes that occur during this switch in cell types.

Solution-processed polymer bilayer heterostructures as hole-transport layers for high-performance opaque and semitransparent organic solar cells

Interfacial layer materials such as hole-transport layers (HTLs) are critical to realizing high-performance organic solar cells (OSCs). However, most OSCs are relying on a prominent HTL material of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with the hygroscopic and acidic feature, which induces poor device stability and limited power conversion efficiencies (PCEs). Here, a novel type of HTLs is developed by combining intrinsically stable poly(triarylamine) (PTAA) with modified PEDOT:PSS for efficient opaque and semitransparent OSCs with good stability. Using diluted solution processing, isopropanol-diluted PEDOT:PSS (ID-PEDOT:PSS) is deposited onto hydrophobic PTAA to improve interfacial compatibility, thereby forming a fitted polymer bilayer heterostructure HTL of PTAA/ID-PEDOT:PSS with high film quality and good transparency. For applications in OSCs with a nonfullerene acceptor (M36), the resulting opaque devices deliver an improved PCE of 14.45%, much higher than 5.72% and 13.21% for the pure PTAA and PEDOT:PSS HTLs-based devices, respectively. The stability of the PTAA/ID-PEDOT:PSS-based OSCs is improved simultaneously, where a normalized PCE for the device after storage over three months retains above 80%, much better than those of devices with other two HTLs. This novel HTL is further used to achieve efficient and stable semitransparent M36-based devices for the first time, exhibiting an outstanding PCE of 12.34% at a high average visible transmittance of 25.56%. Our findings provide an excellent semiconducting interlayer candidate to develop promising opaque and semitransparent OSCs.

Glucose depletion enables Candida albicans mating independently of the epigenetic white-opaque switch

The human fungal pathogen Candida albicans can switch stochastically and heritably between a “white” phase and an “opaque” phase. Opaque cells are the mating-competent form of the species, whereas white cells are thought to be essentially “sterile”. Here, we report that glucose depletion, a common nutrient stress, enables C. albicans white cells to undergo efficient sexual mating. The relative expression levels of pheromone-sensing and mating-associated genes (including STE2/3, MFA1, MFα1, FIG1, FUS1, and CEK1/2) are increased under glucose depletion conditions, while expression of mating repressors TEC1 and DIG1 is decreased. Cph1 and Tec1, factors that act downstream of the pheromone MAPK pathway, play opposite roles in regulating white cell mating as TEC1 deletion or CPH1 overexpression promotes white cell mating. Moreover, inactivation of the Cph1 repressor Dig1 increases white cell mating ~4000 fold in glucose-depleted medium relative to that in the presence of glucose. Our findings reveal that the white-to-opaque epigenetic switch may not be a prerequisite for sexual mating in C. albicans in nature.

Morphogenic plasticity: the pathogenic attribute of Candida albicans

Candida albicans is a commensal organism of the human gastrointestinal tract and a prevalent opportunistic pathogen. It exhibits different morphogenic forms to survive in different host niches with distinct environmental conditions (pH, temperature, oxidative stress, nutrients, serum, chemicals, radiation, etc.) and genetic factors (transcription factors and genes). The different morphogenic forms of C. albicans are yeast, hyphal, pseudohyphal, white, opaque, and transient gray cells, planktonic and biofilm forms of cells. These forms differ in the parameters like cellular phenotype, colony morphology, adhesion to solid surfaces, gene expression profile, and the virulent traits. Each form is functionally distinct and responds discretely to the host immune system and antifungal drugs. Hence, morphogenic plasticity is the key to virulence. In this review, we address the characteristics, the pathogenic potential of the different morphogenic forms and the conditions required for morphogenic transitions.

Fabrication of semi-transparent Cu(In,Ga)Se2 solar cells aided by Bromine etching

This study introduces a straightforward and reproducible fabrication method to achieve micro-structured semi-transparent Cu(In,Ga)Se2 (CIGSe) solar cells by lithography and wet etch techniques. We fabricated a segmented micro-structured solar cell by selective etching of an opaque CIGSe solar cell with bromine and bleach solutions and obtained an array of micro lines from 200 µm to 1000 µm in width separated by transparent spaces, resulting in an overall semi-transparent structure. The CIGSe solar cell lines exhibit a maximum power conversion efficiency of 12.4 % for 1000 µm width, which reduces to 6.8 % for 200 µm wide lines. The obtained values are among the highest reported in the literature for similarly architected devices. Our results are a promising step towards the implementation of building integrated CIGSe photovoltaics as windows.