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Reliability has become an increasingly important issue as photovoltaic technologies mature. However, researching reliability at the nanometer scale is in its infancy; in particular, in-situ studies have not been reported to date. Here, to investigate potential-induced degradation (PID) of solar cell modules, we have developed an in-situ stressing capability with applied high voltage (HV) and high temperature (HT) on an atomic force microscopy (AFM) platform. We designed a sample holder to simultaneously accommodate 1000-V HV and 200 °C HT stressing. Three technical challenges have been overcome along with the development: thermal drift at HT, HV interference with measurement, and arc discharge caused by HV. We demonstrated no observable measurement artifact under the stress conditions. Based on our in-situ stressing AFM, Kelvin probe force microscopy potential imaging revealed the evolution of electrical potential across the junction along with the PID stressing time, which provides vital information to further study the PID mechanism. [ABSTRACT FROM AUTHOR]

Camera imaging techniques have been used for the characterization of Cu(In,Ga)Se2 (CIGS) solar cells. Photoluminescence (PL) imaging shows brightness variations after the deposition of the CIGS layer that persist through CdS deposition and subsequent processing steps to finish the devices. PL and electroluminescence imaging on finished cells show a correlation to the devices' corresponding efficiency and open-circuit voltage (VOC), and dark defect-related spots correspond to bright spots on images from illuminated lock-in thermography (LIT) and forward-bias dark LIT. These image-detected defect areas are weak diodes and shunts. Imaging provides locations of defects detrimental to solar cell performance. Some of these defects are analyzed in more detail by scanning electron microscopy using cross-sectional views. [ABSTRACT FROM AUTHOR]

The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br–I) mixed-halide perovskite (with Br greater than 20%) is critical to create tandem solar cells. However, issues with Br–I phase segregation under solar cell operational conditions (such as light and heat) limit the device voltage and operational stability. This challenge is often exacerbated by the ready defect formation associated with the rapid crystallization of Br-rich perovskite chemistry with antisolvent processes. We combined the rapid Br crystallization with a gentle gas-quench method to prepare highly textured columnar 1.75–electron volt Br–I mixed WBG perovskite films with reduced defect density. With this approach, we obtained 1.75–electron volt WBG PSCs with greater than 20% power conversion efficiency, approximately 1.33-volt open-circuit voltage (Voc), and excellent operational stability (less than 5% degradation over 1100 hours of operation under 1.2 sun at 65°C). When further integrated with 1.25–electron volt narrow-bandgap PSC, we obtained a 27.1% efficient, all-perovskite, two-terminal tandem device with a high Voc of 2.2 volts. [ABSTRACT FROM AUTHOR]

RbF post-deposition treatments have been explored in the literature for increasing the open-circuit voltage, fill factor, and hence the efficiency of Cu(In,Ga)Se 2 solar cells. However, given the few papers documenting the experimental steps, it was difficult to quickly reproduce the results. This contribution describes some of the optimization steps that led to a successful RbF PDT based on device performance. We present results that put boundaries on the temperatures of the RbF cell and the lamp (for sample heating) setpoint. The best recipe for our specific growth process is documented in detail so that others may copy the procedure and possibly arrive at a successful RbF PDT in a reasonable time. • RbF post-deposition treatment of CIGS was more difficult to optimize than KF post-deposition treatment. • The importance of RbF PDT parameters from most to least is RbF cell temperature, substrate temperature, and Se flux. • Successful RbF PDTs were achieved with RbF cell temperature from 505 °C through 555 °C with the best at 540 °C. • Lamp setpoint temperature from 400 °C through 540 °C work for RbF PDTs. • Lists detailed recipe for NREL's best RbF post-deposition treatment. [ABSTRACT FROM AUTHOR]

Radical reduction of III–V device costs requires a multifaceted approach attacking both growth and substrate costs. Implementing device removal and substrate reuse provides an opportunity for substrate cost reduction. Controlled spalling allows removal of thin devices from the expensive substrate; however, the fracture‐based process currently generates surfaces with significant morphological changes compared to polished wafers. 49 single junction devices are fabricated across the spalled surface of full 50 mm germanium wafers without chemo‐mechanical polishing before epitaxial growth. Device defects are identified and related to morphological spalling defects—arrest lines, gull wings, and river lines—and their impact on cell performance using physical and functional characterization techniques. River line defects have the most consistent and detrimental effect on cell performance. Devices achieve a single junction efficiency above 23% and open‐circuit voltage of 1.01 V, demonstrating that spalled germanium does not need to be returned to a pristine, polished state to achieve high‐quality device performance. [ABSTRACT FROM AUTHOR]

Glass/glass (G/G) photovoltaic (PV) module construction is quickly rising in popularity due to increased demand for bifacial PV modules, with additional applications for thin-film and building-integrated PV technologies. G/G modules are expected to withstand harsh environmental conditions and extend the installed module lifespan to greater than 30 years compared to conventional glass/backsheet (G/B) modules. With the rapid growth of G/G deployment, understanding the outdoor performance, degradation, and reliability of this PV module construction becomes highly valuable. In this review, we present the history of G/G modules that have existed in the field for the past 20 years, their subsequent reliability issues under different climates, and methods for accelerated testing and characterization of both cells and packaging materials. We highlight some general trends of G/G modules, such as greater degradation when using poly(ethylene-co-vinyl acetate) encapsulants, causing the industry to move toward polyolefin-based encapsulants. Transparent backsheets have also been introduced as an alternative to the rear glass for decreasing the module weight and aiding the effusion of trapped gaseous degradation products in the laminate. New amendments to IEC 61215 standard protocols for G/G bifacial modules have also been proposed so that the rear side power generation and UV exposure will be standardized. We further summarize a suite of destructive and non-destructive characterization techniques, such as current–voltage scans, module electro-optical imaging, adhesion tests, nanoscale structural/chemical investigation, and forensic analysis, to provide deeper insights into the fundamental properties of the module materials degradation and how it can be monitored in the G/G construction. This will set the groundwork for future research and product development. [ABSTRACT FROM AUTHOR]

The injection-dependent lifetimes of different levels of Ni-contaminated n-type Czochralski (CZ) silicon wafers were investigated using resonant-coupled photoconductance decay (RCPCD) and quasi-steady-state photoconductance technique (QSSPC). The lifetime degradation of the most heavily contaminated samples was caused by Ni silicide precipitates at the surface of the wafers. The impact on lifetime was determined by surface recombination velocities (SRV). SRV values from RCPCD were comparable to those extracted by the QSSPC technique. A direct correlation between minority carrier lifetime and the concentration of electrically active substitutional Ni and Ni silicide precipitate traps measured using deep level transient spectroscopy was established. [ABSTRACT FROM AUTHOR]

We report properties of highly conducting n -type cadmium telluride single crystals doped with iodine (CdTe:I). These crystals were grown with dopant concentrations in the range of 1017 cm−3 to 1019 cm−3 by Modified Vertical Bridgman (MVB) melt growth. Post-growth dopant activation, including Cd annealing, Te annealing, and rapid thermal annealing (RTA), was applied to improve free carrier density. The structural, optical, and electrical properties were analyzed by Glow Discharge Mass Spectroscopy (GDMS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Photoluminescence Spectroscopy (PL), optical absorption, Hall measurements, Capacitance-Voltage (CV) measurements, and time-resolved photoluminescence (TRPL). The results indicate that Cd annealing is the most effective activation method to get 100 % donor activation (n ≈ 2 ×1018 cm−3), which is close to the room temperature solubility limit of iodine. This leads to the lowest resistivity and the highest mobility. Moreover, this data suggests a potential role of Cd vacancy-related defects on electrical self-compensation. • N-type CdTe:I single crystals with 1017-1019 cm−3 iodine produced. • Post-growth annealing (Cd, Te, or Ar) assessed to improve the free carrier density. • Results indicate iodine's room temperature solubility in CdTe is ≈1018 cm−3. • Cd annealing leads to 100 % donor activation with the highest mobility. • Carrier lifetimes of Cd annealed CdTe:I are close to the radiative limit. [ABSTRACT FROM AUTHOR]

Resonant inelastic x-ray scattering (RIXS) at the oxygen K-edge has recently accessed multi-spinon excitations in the one-dimensional antiferromagnet (1D-AFM) Sr2CuO3, where four-spinon excitations are resolved separately from the two-spinon continuum. This technique, therefore, provides new opportunities to study fractionalized quasiparticle excitations in doped 1D-AFMs. To this end, we carried out exact diagonalization studies of the doped t-J model and provided predictions for oxygen K-edge RIXS experiments on doped 1D-AFMs.Weshow that the RIXS spectra are rich, containing distinct two- and four-spinon excitations, dispersive antiholon excitations, and combinations thereof. Our results highlight how RIXS complements inelastic neutron scattering experiments by accessing additional charge and spin components of fractionalized quasiparticles. [ABSTRACT FROM AUTHOR]

Upon doping, Mott insulators often exhibit symmetry breaking where charge carriers and their spins organize into patterns known as stripes. For high–transition temperature cuprate superconductors, stripes are widely suspected to exist in a fluctuating form. We used numerically exact determinant quantum Monte Carlo calculations to demonstrate dynamical stripe correlations in the three-band Hubbard model, which represents the local electronic structure of the copper-oxygen plane. Our results, which are robust to varying parameters, cluster size, and boundary conditions, support the interpretation of experimental observations such as the hourglass magnetic dispersion and the Yamada plot of incommensurability versus doping in terms of the physics of fluctuating stripes. These findings provide a different perspective on the intertwined orders emerging from the cuprates’ normal state. [ABSTRACT FROM AUTHOR]

We developed and applied a new analytical technique—near-field transport imaging (NF-TI or simply TI)—to photovoltaic materials. Charge-carrier transport is an important factor in solar cell performance, and TI is an innovative approach that integrates a scanning electron microscope with a near-field scanning optical microscope, providing the possibility to study luminescence associated with recombination and transport with high spatial resolution. In this paper, we describe in detail the technical barriers we had to overcome to develop the technique for routine application and the data-fitting procedure used to calculate minority-carrier diffusion length values. The diffusion length measured by TI agrees well with the results calculated by time-resolved photoluminescence on well-controlled gallium arsenide (GaAs) thin-film samples. We report for the first time on measurements on thin-film cadmium telluride using this technique, including the determination of effective carrier diffusion length, as well as the first near-field imaging of the effect of a single localized defect on carrier transport and recombination in a GaAs heterostructure. Furthermore, by changing the scanning setup, we were able to demonstrate near-field cathodoluminescence (CL), and correlated the results with standard CL measurements. The TI technique shows great potential for mapping transport properties in solar cell materials with high spatial resolution. [ABSTRACT FROM AUTHOR]

The open circuit voltage (V OC) deficit in Cd(Se,Te)-based photovoltaics remains a critical obstacle for pushing the technology closer to theoretical performance limits. Arsenic doping has become a dominant and promising route to achieve the higher p-type carrier concentrations necessary for higher V OC , but challenges associated with this alternate defect chemistry and higher doping density have hindered progress. Here we show that while arsenic doping enables high carrier concentrations (>1016 cm−3), co-doping with copper can provide a boost to V OC without a significant change to carrier concentration. A large data set is initially used to explore current-voltage and capacitance-voltage trends associated with arsenic doped devices with and without copper. A smaller subset is then used to probe these trends using a wide variety of characterization techniques. Copper is found to facilitate reduced interface recombination and potentially improved bulk absorber characteristics, though the mechanisms for these improvements are not yet clear. Despite the improved performance of co-doped devices, V OC is still far below its potential especially for highly doped devices. Low emitter doping in conjunction with high absorber doping seems to be a plausible cause for this significant deficit, though other device properties may exacerbate this problem. • Cu does not (necessarily) compensate high carrier concentrations in As:Cd(Se,Te). • Advanced characterization of As and Cu related performance limitations in 4 regimes. • High carrier concentration Cd(Se,Te) absorbers are more sensitive to recombination. • Reducing doping near the interface may limit recombination-related Voc loss. [ABSTRACT FROM AUTHOR]

As compounds are optimized for greater potency during pharmaceutical discovery, their aqueous solubility often decreases, making them less viable as orally-administered drugs. To investigate whether potency and insolubility share a common origin, we examined the structural and thermodynamic properties of telaprevir, a sparingly soluble inhibitor of hepatitis C virus protease. Comparison of the hydrogen bond motifs in crystalline telaprevir with those present in the protease–telaprevir complex revealed striking similarities. Additionally, the thermodynamics of telaprevir dissolution closely resembles those of protein–ligand dissociation. Together, these findings point to a common origin of potency and insolubility rooted in particular amide–amide hydrogen bond patterns. The insolubility of telaprevir is shown by computational analysis to be caused by interactions in the crystal, not unfavorable hydrophobic hydration. Accordingly, competing out the particular amide–amide hydrogen bond motifs in crystalline telaprevir with 4-hydroxybenzoic acid yielded a co-crystalline solid with excellent aqueous dissolution and oral absorption. The analysis suggests a generalizable approach for identifying drug candidate compounds that either can or cannot be rendered orally bioavailable by alteration of their crystalline solid phases, in an approach that provides a pragmatic way to attain substantial enhancements in the success rate of drug discovery and development. [ABSTRACT FROM AUTHOR]

The canonical one-band Hubbard model is studied using a computational method that mixes the Monte Carlo procedure with the mean field approximation. This technique allows us to incorporate thermal fluctuations and the development of short-range magnetic order above ordering temperatures, contrary to the crude finite-temperature Hartree-Fock approximation, which incorrectly predicts a Neel temperature TN that grows linearly with the Hubbard U/t. The effective model studied here contains quantum and classical degrees of freedom. It thus belongs to the "spin fermion" model family widely employed in other contexts. Using exact diagonalization, supplemented by the traveling cluster approximation, for the fermionic sector, and classical Monte Carlo for the classical fields, the Hubbard U/ t vs temperature T/ t phase diagram is studied employing large three- and two-dimensional clusters. We demonstrate that the method is capable of capturing the formation of local moments in the normal state without long-range order, the nonmonotonicity of TN with increasing U/t, the development of gaps and pseudogaps in the density of states, and the two-peak structure in the specific heat. Extensive comparisons with determinant quantum Monte Carlo results suggest that the present approach is qualitatively, and often quantitatively, accurate, particularly at intermediate and high temperatures. Finally, we study the Hubbard model including plaquette diagonal hopping (i.e., the t-t' Hubbard model) in two dimensions and show that our approach allows us to study low-temperature properties where determinant quantum Monte Carlo fails due to the fermion sign problem. Future applications of this method include multiorbital Hubbard models such as those needed for iron-based superconductors. [ABSTRACT FROM AUTHOR]

Abstract: Sperm chromatin status was assessed in 565 Zebu and Zebu crossbred beef bulls in extensive tropical environments using the sperm chromatin structure assay (SCSA). The SCSA involved exposure of sperm to acid hydrolysis for 0.5 or 5.0 minutes, followed by flow cytometry to ascertain relative amounts of double-stranded (normal) and single-stranded (denatured) DNA, which was used to generate a DNA fragmentation index (%DFI). With conventional SCSA (0.5-minute SCSA), 513 bulls (91%) had <15 %DFI, 24 bulls (4%) had 15 to 27 %DFI, and 28 bulls (5%) had >27 %DFI. In 5.0-minute SCSA, 432 bulls (76%) had <15 %DFI, 68 bulls (12%) had 15 to 27 %DFI and 65 bulls (12%) had >27 %DFI. For most bulls, the SCSA was repeatable on two to four occasions; however, because most bulls had <15 %DFI, repeatability of the SCSA will need to be determined in a larger number of bulls in the 15 to 27 %DFI and >27 %DFI categories. The %DFI was negatively correlated with several bull semen parameters and the strongest negative correlation was with normal sperm. There was a strong positive correlation between %DFI and sperm head abnormalities. Based on these findings, most Zebu beef bulls in extensive tropical environments had relatively stable sperm chromatin. Based on the apparent negative correlations with conventional semen parameters, we inferred that the SCSA measured a unique feature of sperm quality, which has also been suggested for other species. Further studies on the relationships between sperm chromatin stability and fertility are required in beef bulls before chromatin status can be used as an additional predictor of the siring capacity of individual bulls in extensive multiple-sire herds. [Copyright &y& Elsevier]

We report a high-resolution resonant inelastic soft x-ray scattering study of the quantum magnetic spin- chain materials Li2CuO2 and CuGeO3. By tuning the incoming photon energy to the oxygen K edge, a strong excitation around 3.5 eV energy loss is clearly resolved for both materials. Comparing the experimental data to many-body calculations, we identify this excitation as a Zhang-Rice singlet exciton on neighboring CuO4 plaquettes. We demonstrate that the strong temperature dependence of the inelastic scattering related to this high-energy exciton enables us to probe short-range spin correlations on the 1 meV scale with outstanding sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: Boars fed on ration of 200ppm Zn methionate showed a significant increase (P <0.001) in sperm DNA fragmentation when compared to animals fed on non-supplemented and rations containing 150ppm Zn methionate. There was a positive correlation (R2=0.207; P =0.002) between % sperm DNA fragmentation (SDF) and the concentration of Zn in spermatozoa. Increased Zn in the diet also resulted in a non-proportional increase in Zn concentration in the testis and spermatozoa but not in the epididymis; Zn in sperm accumulated at levels up to 50 times higher than that found in the seminal plasma and 10–13 times that found in the epididymis and testis, respectively. These results show that supplementation of dietary Zn at a concentration of 200ppm had an adverse effect on boar sperm DNA quality and may be related to the ability of spermatozoa to accumulate Zn during spermiogenesis. [Copyright &y& Elsevier]

Abstract: Female koalas (Phascolarctos cinereus) exhibit both homosexual and heterosexual interactions in captivity, even though only heterosexual copulations have been observed in the wild. A key component of sexual interaction is the acoustic bellow, which is produced by males in the wild and both females and males in captivity. We recorded events in both homosexual and heterosexual interactions in a captive koala population, and vocalisations during and outside these interactions. A total of 43 homosexual and 15 heterosexual interactions were recorded in female koalas and were found to have the same principle components following presentation of the mounting male or female to the female: a short delay from neckbite to thrusting, a thrusting phase, followed by a pause and finally jerking behaviour. Thrusting and jerking phases were longest and were of approximately equal length. The delay from neckbite to thrusting, the thrusting phase and the jerking phase were shorter in homosexual than heterosexual mountings, which may relate to the absence of penile intromission and ejaculation. Female koalas exhibited characteristic oestrous and rejection vocalisations that may attract partners or result in them being rejected. The female post-mating calls and calls outside oestrus were longest, followed by female oestrous bellows and male calls, with female rejection calls being the shortest. Rejection calls were higher frequency than the oestrous calls, in particular rejection of a female. Following separation of bellow acoustics into a grunt and a shorter inhalation component, female bellows could be successfully discriminated from male bellows for 64% of the grunt phases, and 71% of the inhalation phases (P <0.001). Most of the variation between individuals was in the duration, rather than the harmonic range, starting or mean frequency, which were similar for both homosexual and heterosexual copulations. It is concluded that homosexual and heterosexual interactions in female koalas contain the same behavioural components, and similar accompanying vocalisations, although the duration of the different components is specific to the gender and stage of copulation. [Copyright &y& Elsevier]

Charge transfer and electron-phonon coupling (EPC) are proposed to be two important constituents associated with enhanced superconductivity in the single unit cell FeSe films on oxide surfaces. Using high-resolution electron energy loss spectroscopy combined with first-principles calculations, we have explored the lattice dynamics of ultrathin FeSe films grown on SrT103. We show that, despite the significant effect from the substrate on the electronic structure and superconductivity of the system, the FeSe phonons in the films are unaffected. The energy dispersion and linewidth associated with the Fe- and Se-derived vibrational modes are thickness and temperature independent. Theoretical calculations indicate the crucial role of antiferromagnetic correlation in FeSe to reproduce the experimental phonon dispersion. Importantly, the only detectable change due to the growth of FeSe films is the broadening of the Fuchs-Kliewer (F-K) phonons associated with the lattice vibrations of SrTiO3(001) substrate. If EPC plays any role in the enhancement of film superconductivity, it must be the interfacial coupling between the electrons in FeSe film and the F-K phonons from substrate rather than the phonons of FeSe. [ABSTRACT FROM AUTHOR]

We studied structural and magnetic ordering in Yb2TiO5 using synchrotron x-ray diffraction, neutron diffraction and total scattering, ac and dc susceptibility, and inelastic neutron scattering. Diffraction measurements reveal an average disordered fluorite structure with additional diffuse scattering features, which are caused by structural short-range orthorhombic order, as evidenced by the neutron pair distribution function measurements. The ac susceptibility measurements show a broad peak at Tf≈0.35 K that displays Arrhenius behavior with an activation energy of 2.51(5) meV. Zero-field neutron scattering measurements show broad magnetic diffuse scattering in the elastic channel with an antiferromagnetic-type gapless excitation extending to 1.5 meV. A polarized state with partial spin order is induced with an applied magnetic field which opens a gapped excitation that increases monotonically with field strength. [ABSTRACT FROM AUTHOR]

We report systematic angle-resolved photoemission (ARPES) experiments using different photon polarizations and experimental geometries and find that the doping evolution of the normal state of Ba(Fe1-xCox)2As2 deviates significantly from the predictions of a rigid band model. The data reveal a nonmonotonic dependence upon doping of key quantities such as band filling, bandwidth of the electron pocket, and quasiparticle coherence. Our analysis suggests that the observed phenomenology and the inapplicability of the rigid band model in Co-doped Ba122 are due to electronic correlations, and not to the either the strength of the impurity potential, or self-energy effects due to impurity scattering. Our findings indicate that the effects of doping in pnictides are much more complicated than currently believed. More generally, they indicate that a deep understanding of the evolution of the electronic properties of the normal state, which requires an understanding of the doping process, remains elusive even for the 122 iron-pnictides, which are viewed as the least correlated of the high-TC unconventional superconductors. [ABSTRACT FROM AUTHOR]

Cuprate materials, such as those hosting high-temperature superconductivity, represent a famous class of materials where the correlations between the strongly entangled charges and spins produce complex phase diagrams. Several years ago, the Zhang-Rice singlet was proposed as a natural quasiparticle in hole-doped cuprates. The occurrence and binding energy of this quasiparticle, consisting of a pair of bound holes with antiparallel spins on the same CuO4 plaquette, depends on the local electronic interactions, which are fundamental quantities for understanding the physics of the cuprates. Here, we employ state-of-the-art resonant inelastic x-ray scattering (RIXS) to probe the correlated physics of the CuO4 plaquettes in the quasi-one-dimensional chain cuprate Li2CuO2. By tuning the incoming photon energy to the O K edge, we populate bound states related to the Zhang-Rice quasiparticles in the RIXS process. Both intra- and interchain Zhang-Rice singlets are observed and their occurrence is shown to depend on the nearest-neighbor spin-spin correlations, which are readily probed in this experiment. We also extract the binding energy of the Zhang-Rice singlet and identify the Zhang-Rice triplet excitation in the RIXS spectra. [ABSTRACT FROM AUTHOR]

A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)]. In this publication we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. We also study a simplified version of the model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. We conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations. [ABSTRACT FROM AUTHOR]

In monocrystalline Si (c-Si) solar cells, identification and mitigation of bulk defects are crucial to achieving a high photoconversion efficiency. To spectroscopically detect defects in the c-Si bulk, it is desirable to passivate the surface defects. Passivation of the c-Si surface with dielectrics such as Al 2 O 3 and SiN x requires deposition at elevated temperatures, which can influence defects in the bulk. Herein, we report on the passivation of different Czochralski (Cz) Si wafer surfaces by an organic copolymer, Nafion. We test the efficacy of the surface passivation at temperatures ranging from 6 to 473 K to detect bulk defects using electron paramagnetic resonance (EPR) spectroscopy. By comparing with state-of-the-art passivation layers, including Al 2 O 3 and liquid HF/HCl, we found that at room temperature, Nafion can provide comparable passivation of n-type Cz Si with an implied open-circuit voltage ( iV oc ) of 713 mV and a recombination current prefactor J 0 of 5 fA/cm 2 . For p-type Cz Si, we obtained an iV oc of 682 mV with a J 0 of 22.4 fA/cm 2 . Scanning electron microscopy and photoluminescence reveal that Nafion can also be used to passivate the surface of c-Si solar cell fragments scribed from a solar cell module by using a laser. Consistent with previous studies, analysis of the EPR spectroscopy data confirms that the H-terminated surface is necessary, and fixed negative charge in Nafion is responsible for the field-effect passivation. While the surface passivation quality was maintained for almost 24 h, which is sufficient for spectroscopic measurements, the passivation degraded over longer durations, which can be attributed to surface SiO x growth. These results show that Nafion is a promising room-temperature surface passivation technique to study bulk defects in c-Si.

The omnipresence of charge density waves (CDWs) across almost all cuprate families underpins a common organizing principle. However, a longstanding debate of whether its spatial symmetry is stripe or checkerboard remains unresolved. While CDWs in lanthanum- and yttrium-based cuprates possess a stripe symmetry, distinguishing these two scenarios is challenging for the short-range CDW in bismuth-based cuprates. Here, high-resolution resonant inelastic x-ray scattering is employed to uncover the spatial symmetry of the CDW in Bi 2 Sr 2 - x La x CuO 6 + δ . Across a wide range of doping and temperature, anisotropic CDW peaks with elliptical shapes are found in reciprocal space. Based on Fourier transform analysis of real-space models, the results are interpreted as evidence of unidirectional charge stripes, hosted by mutually 90°-rotated anisotropic domains. This work paves the way for a unified symmetry and microscopic description of CDW order in cuprates., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br-I) mixed-halide perovskite (with Br greater than 20%) is critical to create tandem solar cells. However, issues with Br-I phase segregation under solar cell operational conditions (such as light and heat) limit the device voltage and operational stability. This challenge is often exacerbated by the ready defect formation associated with the rapid crystallization of Br-rich perovskite chemistry with antisolvent processes. We combined the rapid Br crystallization with a gentle gas-quench method to prepare highly textured columnar 1.75-electron volt Br-I mixed WBG perovskite films with reduced defect density. With this approach, we obtained 1.75-electron volt WBG PSCs with greater than 20% power conversion efficiency, approximately 1.33-volt open-circuit voltage ( V oc ), and excellent operational stability (less than 5% degradation over 1100 hours of operation under 1.2 sun at 65°C). When further integrated with 1.25-electron volt narrow-bandgap PSC, we obtained a 27.1% efficient, all-perovskite, two-terminal tandem device with a high V oc of 2.2 volts.

Glass/glass (G/G) photovoltaic modules are quickly rising in popularity, but the durability of modern G/G packaging has not yet been established. In this work, we examine the interfacial degradation modes in G/G and glass/transparent backsheet modules under damp heat (DH) with and without system bias voltage, comparing emerging polyolefin elastomer (POE) and industry-standard poly(ethylene-co-vinyl acetate) (EVA) encapsulants. We investigate the transport of ionic species at cell/encapsulant interfaces, demonstrating that POE limits both sodium and silver ion migration compared with EVA. Changes to the chemical structures of the encapsulants at the cell/encapsulant interfaces demonstrate that both POE and EVA are more susceptible to degradation in modules with a transparent backsheet than in the G/G configuration. Adhesion testing reveals that POE and EVA have comparable critical debond energies after the DH exposures regardless of system bias polarity. The results of this study indicate that the interfacial degradation mechanisms of G/G appear to be similar to those of conventional glass/backsheet modules. For emerging materials, our results demonstrate that POE offers advantages over EVA but that transparent backsheets may accelerate encapsulant degradation due to increased moisture ingress when compared with the G/G structure., (© 2022 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.)

The pursuit of ever-higher solar cell efficiencies has focused heavily on multijunction technologies. In tandem cells, subcells are typically either contacted via two terminals (2T) or four terminals (4T). Simulations show that the less-common three-terminal (3T) design may be comparable to 4T tandem cells in its compatibility with a range of materials, operating conditions, and methods for subcell integration, yet the 3T design circumvents shading losses of the 4T intermediate conductive layers. This study analyzes the performance of two superstrate 3T III-V-on-Si (III-V//Si) tandem cells: One has slightly greater current contribution from the Si bottom cell (GaInP//Si) and the other has substantially greater current contribution from the GaAs top cell (GaAs//Si). Our results show that both tandem cells exhibit the same efficiency (21.3%), thereby demonstrating that the third terminal allows for flexibility in the selection of the top cell material, similar to the 4T design., Competing Interests: Emily Warren and Adele Tamboli hold a patent related to III-V/Si tandem cells: US10256093B2. Kaitlyn VanSant is currently a NASA Postdoc Program Fellow, affiliated with NASA’s Glenn Research Center., (© 2022 The Author(s).)