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Although trachoma mass drug administration (MDA) programs target ocular Chlamydia trachomatis, the global trachoma control program does not monitor infection as a measure of impact but instead relies on monitoring clinical indicators. This study aimed to monitor the prevalence of ocular C. trachomatis among a population-based sample of children ages 1–5 years throughout Amhara, Ethiopia, a region that has received approximately 8 years of annual MDA as part of trachoma control. Between 2014 and 2021, trachoma impact surveys and surveillance surveys were conducted in all 156 districts of Amhara using a multistage cluster randomized methodology. Certified graders assessed individuals ages ≥ 1 year for trachomatous inflammation-follicular (TF), and a random subset of children ages 1–5 years also provided a conjunctival swab. Polymerase chain reaction was used to test for C. trachomatis. A total of 28,410 conjunctival swabs were collected from children ages 1–5 years across Amhara. The regional C. trachomatis infection prevalence was 4.7% (95% uncertainty interval: 4.3–5.1%). Infection was detected in all 10 zones of the region and ranged from 0.2% in Awi Zone to 11.9% in Waghemra Zone. Infection was detected in 17 (26%) districts with a TF prevalence < 10% and in 7 (21%) districts with a TF prevalence < 5%. Through programmatic monitoring of C. trachomatis infection, this study demonstrated that considerable infection remained throughout Amhara despite approximately 8 years of trachoma interventions and that enhanced interventions such as more frequent than annual MDA will be needed if elimination thresholds are to be reached.

Author(s): Sood, Mohit; Urbaniak, Aleksander; Boumenou, Christian Kameni; Weiss, Thomas; Elanzeery, Hossam; Babbe, Finn; Werner, Florian; Melchiorre, Michele; Siebentritt, Susanne | Abstract: The presence of interface recombination in a complex multilayered thin-film solar structure causes a disparity between the internal open-circuit voltage (VOC,in), measured by photoluminescence, and the external open-circuit voltage (VOC,ex) i.e. an additional VOC deficit. Higher VOC,ex value aim require a comprehensive understanding of connection between VOC deficit and interface recombination. Here, a deep near-surface defect model at the absorber/buffer interface is developed for copper indium di-selenide solar cells grown under Cu excess conditions to explain the disparity between VOC,in and VOC,ex.. The model is based on experimental analysis of admittance spectroscopy and deep-level transient spectroscopy, which show the signature of deep acceptor defect. Further, temperature-dependent current-voltage measurements confirm the presence of near surface defects as the cause of interface recombination. The numerical simulations show strong decrease in the local VOC,in near the absorber/buffer interface leading to a VOC deficit in the device. This loss mechanism leads to interface recombination without a reduced interface bandgap or Fermi level pinning. Further, these findings demonstrate that the VOC,in measurements alone can be inconclusive and might conceal the information on interface recombination pathways, establishing the need for complementary techniques like temperature dependent current voltage measurements to identify the cause of interface recombination in the devices.

Doping in the chalcopyrite Cu(In,Ga)Se2 is determined by intrinsic point defects. In the ternary CuInSe2, both N-type conductivity and P-type conductivity can be obtained depending on the growth conditions and stoichiometry: N-type is obtained when grown Cu-poor, Se-poor, and alkali-free. CuGaSe2, on the other hand, is found to be always a P-type semiconductor that seems to resist all kinds of N-type doping, no matter whether it comes from native defects or extrinsic impurities. In this work, we study the N-to-P transition in Cu-poor Cu(In,Ga)Se2 single crystals in dependence of the gallium content. Our results show that Cu(In,Ga)Se2 can still be grown as an N-type semiconductor until the gallium content reaches the critical concentration of 15%–19%, where the N-to-P transition occurs. Furthermore, trends in the Seebeck coefficient and activation energies extracted from temperature-dependent conductivity measurements demonstrate that the carrier concentration drops by around two orders of magnitude near the transition concentration. Our proposed model explains the N-to-P transition based on the differences in formation energies of donor and acceptor defects caused by the addition of gallium.

Cu(In,Ga)Se2 based solar cells exceed power conversion efficiencies of 23 %. Yet, the fill factor of these solar cells, with best values around 80 %, is relatively low (Si reaches 84.9%) mostly due to diode factors greater than one. Recently, we proposed metastable defects, a general feature of the Cu(In,Ga)Se2 alloy, to be the origin of the increased diode factor. We measure the diode factor of the bare absorber layers by excitation-dependent photoluminescence. For high quality and thus high luminescent polycrystalline absorbers, we evaluate the diode factor excitation dependence over four orders of magnitude. Using simulations and the model of metastable defects, we can well describe the experimental findings on n- and p-type epitaxial films as well as the polycrystalline absorbers, providing additional evidence for this model. We find that the diode factors measured optically by photoluminescence impose a lower limit for the diode factor measured electrically on a finished solar cell. Interestingly, the lowest diode factor (optical and electrical) and consequently highest fill factor of 81.0 % is obtained by Ag alloying, i.e. an (Ag,Cu)(In,Ga)Se2 absorber. This finding hints to a pathway to increase fill factors and thus efficiencies for Cu(In,Ga)Se2-based solar cells.

Ultra-fast thermal annealing of semiconductor materials using a laser can be revolutionary for short processing times and low manufacturing costs. Here we investigate Cu–In–Se thin films as precursors for CuInSe2 semiconductor absorber layers via laser annealing. The reaction mechanism of laser annealed metal stacks is revealed by measuring ex situ X-ray diffractograms, Raman spectra and composition. It is shown that the formation of CuInSe2 occurs via the formation of CuxSe/InxSey binary phases as in conventional annealing routes, despite the entirely different annealing time scale. Pre-alloying the Cu and In metals prior to laser annealing significantly enhances the selenisation reaction rate. Laser annealing for six seconds approaches a near phase-pure material, which exhibits similar crystalline quality to the reference material annealed for ninety minutes in a tube furnace. The estimated quasi Fermi level splitting deficit for the laser annealed material is only 60 meV lower than the reference sample, which implies a high optoelectronic quality.

BACKGROUND Surveillance data are an essential public health resource for guiding policy and allocation of human and capital resources. These data often consist of large collections of information based on non-random sample designs. Population estimates based on such data may be impacted by the underlying sample distribution compared to the true population of interest. Here we simulate a population of interest and allow response rates to vary in non-random ways to illustrate and measure the effect this has on population-based estimates of an important public health policy outcome. OBJECTIVE To explore the effects of non-random missing data on surveillance-based population estimates. METHODS We simulate a population of respondents answering a survey question about their satisfaction with their community’s policy regarding vaccination mandates for government personnel. We allow response rates to differ between the generally satisfied and dissatisfied and consider the effect of common efforts to control for potential bias: sampling weights, sample size inflation and hypothesis tests for determining missingness at random. We compare these conditions via mean squared errors and sampling variability to characterize the bias in estimation arising under these different approaches. RESULTS Sample estimates present clear, quatifiable bias, even in the most favorable response profile. Efforts to mitigate bias through sample size inflation and sampling weights have negligible effect on the overall result. Additionally, hypothesis testing for departures from random missingness rarely detect the non-random missingness across the widest range of response profiles considered. CONCLUSIONS Our results suggest that assuming surveillance data are missing at random during analysis could provide estimates that are widely different from what we might see in the whole population. Policy decisions based on such potentially biased estimates could result in devastating results in terms of community disengagement and health disparities. Alternative approaches to analysis which move away from broad generalization of a mis-measured population at risk are necessary to identify the marginalized groups where overall response may be very different from those observed in the measured respondents.

Metastable defects can decisively influence the diode factor and thus the efficiency of a solar cell. The diode factor is also influenced by the doping level and the recombination mechanisms in the solar cell. Here we quantify how the various parameters change the diode factor by photoluminescence measurements and simulations. In addition, we show that backside recombination reduces the open circuit voltage in CuInSe2 solar cells by more than 40 mV. Passivation by a Ga gradient is shown to be as efficient as a passivation by dielectric layers. Increased backside recombination reduces the diode factor, not because of less metastable defect transformation but because of a sublinear increase in photo generated carriers with excitation. This reduction in diode factor is unwanted, since the increased recombination reduces the voltage. A higher doping level, on the other hand, reduces the diode factor, thereby increasing the fill factor, and at the same time increases the voltage.

To achieve a high fill factor, a small diode factor close to 1 is essential. The optical diode factor determined by photoluminescence is the diode factor from the neutral zone of the solar cell and thus a lower bound for the diode factor. Due to metastable defects transitions, the optical diode factor is higher than 1 even at low excitation. Here, the influence of the backside recombination and the doping level on the optical diode factor are studied. First, photoluminescence and solar cell capacitance simulator (SCAPS) simulations are used to determine the back surface recombination velocity of Cu(In, Ga)Se2 with various back contacts and different doping levels. Then, experimental results and simulations show that both back surface recombination and high doping density reduce the optical diode factor. The back surface recombination reduces the optical diode factor with undesirable extra nonradiative recombination. The smaller value achieved by higher doping can increase quasi-Fermi level splitting at the same time. The simulations show that the back surface recombination reduces the optical diode factor due to an illumination-dependent recombination rate. In addition, a higher majority carrier doping reduces the influence of majority carrier gain from metastable defect transitions, thus reducing the optical diode factor.

Nasarawa and Plateau states of north-central Nigeria have implemented programs to control schistosomiasis (SCH) and soil-transmitted helminths (STH) in children since the 1990s. Statewide mapping surveys were conducted in 2013, when 11,332 school-aged children were sampled from 226 schools. The local government areas (LGAs) then received varying combinations of mass drug administration (MDA) for the next 5 years. We revisited 196 (87%) schools in 2018 plus an additional six (202 schools in total), sampling 9,660 children. We calculated overall prevalence and intensity of infection and evaluated associations with gender; age; behaviors; water, sanitation, and hygiene (WASH); and treatment regimen. Urine heme detection dipsticks were used for Schistosoma hematobium in both surveys, with egg counts added in 2018. Stool samples were examined by Kato-Katz for Ascaris lumbricoides, Trichuris trichiura, Schistosoma mansoni, and hookworm. Schistosomiasis prevalence among sampled students dropped from 12.9% (95% confidence interval [CI]: 11.1–14.9%) to 9.0% (95% CI: 7.5–10.9%), a statistically significant change (P < 0.05). In 2018, eight LGAs still had > 1% of children with heavy-intensity schistosome infections. Prevalence of STH infection did not significantly change, with 10.8% (95% CI: 9.36–12.5%) of children positive in 2013 and 9.4% (95% CI: 8.0–10.9%) in 2018 (P = 0.182). Heavy-intensity STH infections were found in < 1% of children with hookworm, and none in children with A. lumbricoides or T. trichiura in either study. The WASH data were collected in 2018, indicating 43.6% of schools had a latrine and 14.4% had handwashing facilities. Although progress is evident, SCH remains a public health problem in Nasarawa and Plateau states.

$\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{S}}_{2}$ is a promising semiconductor that offers excellent prospects for photovoltaics. However, the performance has been plagued mostly due to large photovoltage deficit. Here, we investigate defects and optoelectronic properties of 1.7-eV band gap near-stoichiometric $\mathrm{Cu}(\mathrm{In},\mathrm{Ga}){\mathrm{S}}_{2}$ (CIGS). We have estimated quasi-Fermi-level splitting of 921 meV from steady state photoluminescence (PL) measurements at 1 sun. Detailed analysis of temperature and excitation dependent PL reveals the behavior of a strongly compensated semiconductor. We show that spatially varying energetic disorder, described by electrostatic potential fluctuations, causes band-tail recombination and strongly affects the carrier recombination in compensated CIGS. Apart from band-tail transitions, we also observe two deep defects at about 0.3 and 0.45 eV below the band edge. The defects are also discerned by admittance measurements. Temperature dependent current-voltage measurements show that the open-circuit voltage is further limited by interface recombination. Thus, the performance improvement lies in the mitigation of deep defect states and absorber/buffer interface optimization.

Polycrystalline $(\mathrm{Sb},\mathrm{Bi}{)}_{2}{\mathrm{Se}}_{3}$ thin-film semiconductors are grown by coevaporation with a subsequent annealing process. It is shown that $\mathrm{Bi}$ can be incorporated into the ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$ lattice, substituting up to approximately 60% of the $\mathrm{Sb}$ atoms, while maintaining the orthorhombic crystal structure. Upon $\mathrm{Bi}$ substitution, the lattice expands mainly along the one-dimensional $(\mathrm{Sb},\mathrm{Bi}{)}_{4}{\mathrm{Se}}_{6}$ ribbons. In addition, the band gap decreases with a direct (indirect) band gap of 0.891 eV (0.864 eV) for a $({\mathrm{Sb}}_{0.4},{\mathrm{Bi}}_{0.6}{)}_{2}{\mathrm{Se}}_{3}$ thin film. A photovoltaic device based on a $(\mathrm{Sb},\mathrm{Bi}{)}_{2}{\mathrm{Se}}_{3}$ absorber is fabricated that displays an open-circuit voltage of 133 mV and a short-circuit current density of $18.4\phantom{\rule{0.1em}{0ex}}\mathrm{mA}/{\mathrm{cm}}^{2}$, demonstrating the potential of this material for infrared detection or multijunction solar-cell applications.

Chalcopyrite solar cells achieve efficiencies above 23%. The latest improvements are due to post-deposition treatments (PDT) with heavy alkalis. This study provides a comprehensive description of the effect of PDT on the chemical and electronic structure of surface and bulk of Cu(In,Ga)Se-2. Chemical changes at the surface appear similar, independent of absorber or alkali. However, the effect on the surface electronic structure differs with absorber or type of treatment, although the improvement of the solar cell efficiency is the same. Thus, changes at the surface cannot be the only effect of the PDT treatment. The main effect of PDT with heavy alkalis concerns bulk recombination. The reduction in bulk recombination goes along with a reduced density of electronic tail states. Improvements in open-circuit voltage appear together with reduced band bending at grain boundaries. Heavy alkalis accumulate at grain boundaries and are not detected in the grains. This behavior is understood by the energetics of the formation of single-phase Cu-alkali compounds. Thus, the efficiency improvement with heavy alkali PDT can be attributed to reduced band bending at grain boundaries, which reduces tail states and nonradiative recombination and is caused by accumulation of heavy alkalis at grain boundaries. This work was supported by the European Union's Horizon 2020 research and innovation program under grant agreement no. 641004 (Sharc25) and by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15.0158. Siebentritt, S (reprint author), Univ Luxembourg, Lab Photovolta, Phys & Mat Sci Res Unit, 41 Rue Brill, L-4422 Belvaux, Luxembourg. susanne.siebentritt@uni.lu

Thin film Cu(In,Ga)Se2 (CIGS) solar modules can be grown on flexible and lightweight substrates allowing their direct integration into building elements. Such multifunctional building elements would significantly reduce the installation cost of photovoltaic systems provided that CIGS solar cells with high conversion efficiency can be obtained. Also, there is a need for low cost substrate foil. Mild steel is a promising low cost substrate material due to its excellent mechanical stability and already wide acceptance as component in building envelopes and in numerous other applications. During the growth of the CIGS absorber layer certain elements, e.g. iron, can diffuse from the metallic substrate into the semiconductor deteriorating the device performance. Here we present an effective diffusion barrier and device architecture for processing of highly efficient CIGS solar cells on mild steel substrates. The CIGS absorber layers were grown on mild steel foils by a multistage co-evaporation process at different substrate temperatures. The mild steel substrates were plated with an industrially scalable electrodeposited Ni/Cr bi-layer. The diffusion barrier layer properties of this Ni/Cr coating were investigated directly by measuring the metallic impurities within the absorber by secondary ion mass spectrometry and indirectly by admittance spectroscopy. The Ni/Cr bi-layer was found to be effective up to a nominal CIGS growth temperature of 500 °C. A certified cell efficiency of 18.0% was achieved on a Ni/Cr coated mild steel substrate using a low temperature CIGS deposition process and a NaF and RbF post deposition treatment method.

Sodium is typically used during the synthesis of kesterite thin films to enhance the performance of solar cells. As sodium tends to affect grain growth and morphology, it is difficult to analyse solely the electronic effects of sodium as dopant. To decouple the structural and electronic effects from each other, two processes were designed in this work to successfully incorporate sodium into a vacuum-processed Cu2ZnSnSe4absorber without changing the morphology. A thin layer of NaF is deposited before precursor deposition (Pre-NaF) or after absorber synthesis to undergo a post deposition treatment (NaF-PDT). While composition and distribution of matrix elements remain unchanged, the sodium concentration is increased upon sodium treatment up to 140 ppm as measured by inductively coupled plasma mass spectrometry. X-ray photoelectron spectroscopy showed that the surface composition was not altered. Within its detection limit, sodium was not present at the absorber surface. For a Pre-NaF sample measured with atom probe tomography a sodium concentration of 30 ppm was measured in a grain, suggesting that sodium might segregate at grain boundaries. The additional sodium content in the film leads to an increased acceptor concentration, which results in improved open-circuit voltage and fill factor., Financial support from the Swiss National Science Foundation (SNF) in the network of the Indo-Swiss Joint Research Programme (ISJRP) [IZLIZ2_157140/1] is gratefully acknowledged. T. Schwarz is grateful for the support of the German Research Foundation (DFG) [Contract GA 2450/1-1]. R. Caballero acknowledges financial support from Spanish MINECO within the Ramón y Cajal program [RYC-2011-08521], MINECO project WINCOST [ENE2016-80788-C5-2-R] and from Spanish Ministry of Education, Culture and Sport within the José Castillejo program [CAS 15/00070]

The application of TiO2 as part of the buffer layer stack in thin film Cu(In,Ga)Se2 (CIGS) solar cells is investigated for the improvement of the photovoltaic device performance. In a standard device configuration a CdS/ZnO/Al:ZnO layer stack is applied onto the CIGS absorber layer. By decreasing the CdS buffer layer thickness a higher photocurrent is expected from a reduced parasitic absorption. When the CdS layer is not fully covering the CIGS surface, losses in VOC and FF are observed in I-V measurements due to the arising unfavorable CIGS/ZnO band alignment and sputter damage on the CIGS surface. Here we present thin TiO2 layers deposited by atomic layer deposition at low temperature as alternative to the unintentionally doped ZnO. With this approach, the photocurrent can be increased without adversely affecting VOC. Comparable device efficiency is achieved for the investigated structure and the reference process with the gain in current density being compensated by increased series resistance. Temperature dependent I-V measurements coupled with 1D-SCAPS simulations suggest a positive conduction band offset at the CdS/TiO2 interface limiting the FF. ALD-TiO2 is suggested as a more suitable intermediate buffer layer than sputtered ZnO when thin CdS buffer layers are applied.

The efficiency of solar cells depends on the photocurrent, on the open circuit voltage and on the fill factor, which in turn depends on the diode factor. We review how photoluminescence measurements on the absorber, without finishing the solar cell, reveal the maximum open circuit voltage and the best diode factor, that can be reached in the finished device. We discuss two different ways to extract the quasi Fermi level splitting from absolute calibrated photoluminescence spectra, measured at a one-sun excitation. The absorption spectrum of the solar cell absorber can be extracted from the photoluminescence spectra and allows the reliable determination of tail states. Tail states are responsible for radiative and non-radiative losses in the quasi Fermi level splitting. In the ideal case the open circuit voltage is given by the quasi Fermi level splitting. However, recombination at the interface can reduce the open circuit voltage severely. We discuss various electronic structures at the interface that lead to a reduction of the open circuit voltage. The excitation dependence of the photoluminescence allows to determine the diode factor of the absorber alone, which would be 1 in the ideal case. Metastable defects can increase the diode factor, even for recombination in the neutral zone and for low excitation. This effect decreases the fill factor of the solar cell.

Polycrystalline thin films of (Sb0.42Bi0.58)2Se3 are prepared by co-evaporation in a two-step process. First, the semiconducting layer is grown at 240°C. Subsequently the films are annealed in-situ at various temperatures. The incorporation of Bi into the orthorhombic Sb2Se3 system reduces the bandgap and thus widens the range for infrared detection. It is found that thin film layers can be prepared single phase, while a decomposition is observed for temperatures exceeding 440°C, where the rhombohedral structure of Bi2Se3 forms in addition. Photoluminescence measurements show an increased optoelectronic quality of the films with increasing annealing temperature. However, the luminescence signal reduces when the films decompose into the orthorhombic and the rhombohedral phases.

International audience; In the fields of nanoscience and nanotechnology, it is important to be able to functionalize surfaces chemically for a wide variety of applications. Scanning tunneling microscopes (STMs) are important instruments in this area used to measure the surface structure and chemistry with better than molecular resolution. Self-assembly is frequently used to create monolayers that redefine the surface chemistry in just a single-molecule-thick layer. Indeed, STM images reveal rich information about the structure of self-assembled monolayers since they convey chemical and physical properties of the studied material. In order to assist in and to enhance the analysis of STM and other images, we propose and demonstrate an image-processing framework that produces two image segmentations: one is based on intensities (apparent heights in STM images) and the other is based on textural patterns. The proposed framework begins with a cartoon+texture decomposition, which separates an image into its cartoon and texture components. Afterward, the cartoon image is segmented by a modified multiphase version of the local Chan-Vese model, while the texture image is segmented by a combination of 2D empirical wavelet transform and a clustering algorithm. Overall, our proposed framework contains several new features, specifically in presenting a new application of cartoon+texture decomposition and of the empirical wavelet transforms and in developing a specialized framework to segment STM images and other data. To demonstrate the potential of our approach, we apply it to actual STM images of cyanide monolayers on Au\{111\} and present their corresponding segmentation results.

Multi-junction solar cells are known to have a considerably increased efficiency potential over their typical single junction counterparts. In order to produce low cost and lightweight multi-junction devices, the availability of suitable narrow ( In this contribution we report on the RbF post deposition treatment of narrow bandgap CIGS absorbers grown with a single bandgap grading approach. We discuss the necessary deposition conditions and the observed improvements on solar cells performance. A certified record efficiency of 18.0% for an absorber with 1.00 eV optoelectronic bandgap is presented and its suitability for perovskite/CIGS tandem devices is shown.

This review summarizes the current status of Cu(In,Ga)(S,Se)2 (CIGS) thin film solar cell technology with a focus on recent advancements and emerging concepts intended for higher efficiency and novel applications. The recent developments and trends of research in laboratories and industrial achievements communicated within the last years are reviewed, and the major developments linked to alkali post deposition treatment and composition grading in CIGS, surface passivation, buffer, and transparent contact layers are emphasized. Encouraging results have been achieved for CIGS-based tandem solar cells and for improvement in low light device performance. Challenges of technology transfer of lab's record high efficiency cells to average industrial production are obvious from the reported efficiency values. One section is dedicated to development and opportunities offered by flexible and lightweight CIGS modules. Copyright © 2016 John Wiley & Sons, Ltd.