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Wide bandgap halide perovskite materials show promising potential to pair with silicon bottom cells. To date, most efficient wide bandgap perovskites layers are fabricated by spin coating, which is difficult to scale up. Here, we report on slot die coating for an efficient, 1.68 eV wide bandgap triple halide 3halide perovskite absorber, Cs0.22FA0.78 Pb I0.85Br0.15 3 5 mol MAPbCl3. A suitable solvent system is designed specifically for the slot die coating technique. We demonstrate that our fabrication route is suitable for tandem solar cells without phase segregation. The slot die coated wet halide perovskite is dried by a nitrogen N2 knife with high reproducibility and avoiding antisolvents. We explore varying annealing conditions and identify parameters allowing crystallization of the perovskite film into large grains reducing charge collection losses and enabling higher current density. At 150 C, an optimized trade off between crystallization and the PbI2 aggregates on the film s top surface is found. Thus, we improve the cell stability and performance of both single junction cells and tandems. Combining the 3halide top cells with a 120 amp; 956;m thin saw damage etched commercial Czochralski industrial wafer, a 2 terminal monolithic tandem solar cell with a PCE of 25.2 on a 1 cm2 active area is demonstrated with fully scalable processes

The performance of a superstrate TiO2/Sb2Se3 solar cell, fabricated by close-spaced sublimation technique (CSS), was improved after the deployment of a seed layer. The seed layer caused columnar Sb2Se3 film growth with texture coefficient analysis (TC) showing increased presence of crystal planes, which are inclined towards the [001] crystal direction. Given the highly anisotropic properties of Sb2Se3, preferential growth of (Sb4Se6)n ribbons along the [001] direction is best suited for effective charge collection. Hence, grain orientation of Sb2Se3 films was studied more closely via measurement of pole figures by XRD and orientation distribution maps by electron backscatter diffraction (EBSD). Although the measurements did not reveal strong preferred orientation, it was observed that the columnar Sb2Se3 growth enhanced texture along the [001] direction. Temperature-dependent admittance spectroscopy (TAS) and capacitance–voltage (CV) profiling were performed on the seed-assisted TiO2/Sb2Se3 solar cell to evaluate carrier density and deep defects in the Sb2Se3 absorber. TAS study revealed a deep defect with activation energy of 0.39 eV. CV profiles indicated that the density of defects could be as high as 1017 cm−3, which needs to be addressed by post-deposition treatments.

This work investigates halide segregation in methylammonium-free wide bandgap perovskites by photoluminescence quantum yield (PLQY) and advanced electron microscopy techniques. Our study reveals ho...

Individual grains of chalcopyrite solar cell absorbers can facet in different crystallographic directions at their surfaces. To gain a deeper understanding of the junction formation in these devices, we correlate variations in the surface facet orientation with the defect electronic properties. We use a combined analytical approach based on scanning tunneling spectroscopy (STS), scanning electron microscopy, and electron back scatter diffraction (EBSD), where we perform these experiments on identical surface areas as small as 2 × 2 µm2 with a lateral resolution well below 50 nm. The topography of the absorber surfaces indicates two main morphological features: micro-faceted, long basalt-like columns and their short nano-faceted terminations. Our STS results reveal that the long columns exhibit spectral signatures typical for the presence of pronounced oxidation-induced surface dipoles in conjunction with an increased density of electronic defect levels. In contrast, the nano-faceted terminations of the basalt-like columns are largely passivated in terms of electronic defect levels within the band gap region. Corresponding crystallographic data based on EBSD experiments show that the surface of the basalt-like columns can be assigned to intrinsically polar facet orientations, while the passivated terminations are assigned to non-polar planes. Ab-initio calculations suggest that the polar surfaces are more prone to oxidation and resulting O-induced defects, in comparison to non-polar planes. Our results emphasize the correlation between morphology, surface facet orientations and surface electronic properties. Furthermore, this work aids in gaining a fundamental understanding of oxidation induced lateral inhomogeneities in view of the p-n junction formation in chalcopyrite thin-film solar cells.

The phase mixture CsPb2Br5/CsPbBr3 has raised interest as a promising material system for light emission, light detection, and even for photovoltaic devices owing to its high luminescence yield and...

International audience; In Cu(In,Ga)Se 2 (CIGS) thin-film solar cells, laterally inhomogeneous distributions of point defects may induce electrostatic potential fluctuations and thus reduce the open-circuit voltage (V oc). In the present work, we investigate possible origins of fluctuating potentials and estimate the amplitude of fluctuations and V oc losses in solar cells with various [Ga] in the CIGS absorber, with different buffer layers and with different durations of an RbF postdeposition treatment (PDT). Electron-beam-induced current measurements were employed to study the local difference in the width of the space-charge region (w SCR). It is shown that the amplitude of fluctuations in the w SCR depends significantly on the choice of buffer system and on the duration of the RbF PDT. In addition, energy-dispersive X-ray spectroscopy and cat-hodoluminescence measurements reveal that band-gap fluctuations do not have substantial impact on the device performance. Finally, some of the investigated cells were exposed to light soaking, which was found to be a means to reduce the detected electrostatic potential fluctuations and also to increase the effective electron diffusion length in the CIGS absorber for a part of the investigated cells.

The present work comprises a practical tutorial on the topic of correlative microscopy and its application to optoelectronic semiconductor materials and devices. For the assessment of microscopic structure–property relationships, correlative electron microscopy, combined also with scanning-probe and light microscopy, exhibits a collection of indispensable tools to analyze various material and device properties. This Tutorial describes not only the various microscopy methods but also the specimen preparation in detail. Moreover, it is shown that electron microscopy can serve to monitor phase segregation processes on various length scales in semiconductor nanoparticles and thin films. Algorithms used to extract phase information from high-resolution transmission electron micrographs are explained.

It is attractive to alloy Cu(In,Ga)Se2 solar-cell absorbers with Ag (ACIGSe), since they lead to similar device performances as the Ag-free absorber layers, while they can be synthesized at much lower deposition temperatures. However, a KF post-deposition treatment (PDT) of the ACIGSe absorber surface is necessary to achieve higher open-circuit voltages (Voc). The present work provides microscopic insights to the effects of this KF PDT, employing correlative scanning-electron microscope techniques on identical positions of cross-sectional specimens of the cell stacks. We found that the increase in Voc after the KF PDT can be explained by the removal of Cu-poor, Ag-poor, and Ga-rich regions near the ACIGSe/CdS interface. The KF PDT leads, when optimally doped, to a very thin K-Ag-Cu-Ga-In-Se layer between ACIGSe and CdS. If the KF dose is too large, we find that Cu-poor and K-rich regions form near the ACIGSe/CdS interface with enhanced nonradiative recombination which explains a decrease in the Voc. This effect occurs in addition to the presence of a (K,Ag,Cu)InSe2 intermediate layer, that might be responsible for limiting the short-current density of the solar cells due to a current blocking behavior. Title in Web of Science: Microscopic insight into the impact of the KF post-deposition treatment on optoelectronic properties of (Ag,Cu)(In,Ga)Se-2 solar cells

Transparent conductive materials based on indium oxide remain yet irreplaceable in various optoelectronic applications. Amorphous oxides appear especially attractive for technology as they are isotropic, demonstrate relatively high electron mobility and can be processed at low temperatures. Among them is indium zinc oxide IZO with a large zinc content that is crucial for keeping the amorphous state but redundant for the doping. In this work we investigated water free and water containing IZO films obtained by radio frequency sputtering. The correlation between temperature driven changes of the chemical state, the optical and electrical properties as well as the progression of crystallization was in focus. Such characterization methods as scanning electron microscopy, X ray diffraction, X ray photoelectron spectroscopy, Raman spectroscopy, temperature dependent Hall effect measurements and others were applied. Temperature dependent electrical properties of amorphous IZO and IZO H2O films were found to evolve similarly. Based on our experience in In2O3 H2O In2O3 H or IOH we proposed an explanation for the changes observed. Water admixture was found to decrease crystallization temperature of IZO significantly from amp; 8764; 550 C to amp; 8764; 280 C. Herewith, the presence and concentration of water and or hydroxyls was found to determine Zn distribution in the film. In particular, Zn enrichment was detected at the film s surface respective to the high water and or hydroxyl amount. Raman spectra revealed a two dimensional crystallization of w ZnO which precedes regardless water presence an extensive In2O3 crystallization. An abrupt loss of electron mobility as a result of crystallization was attributed to the formation of ZnO interlayer on grain boundaries

In recent years, inorganic cesium amp; 8722;lead amp; 8722;halide perovskites, CsPbX3 X I, Br, Cl , have attracted interest for optoelectronic applications such as highly efficient thin film light emitting diodes or wide gap absorber materials for photovoltaics. However, phase segregation and secondary phases in as deposited thin films are still considered to be limiting factors for devices based on CsPbX3. Here, we report a correlative electron microscopy and spectroscopy approach for the identification of secondary phases and their distributions in Cs amp; 8722;Pb amp; 8722;Br thin films, deposited by solutionbased and coevaporation methods on various substrates. We identified phases by their compositional, structural, and optoelectronic properties, using X ray diffraction, spectroscopy, and a variety of microscopy techniques. We found that the Cs amp; 8722;Pb amp; 8722;Br films contain ternary Cs4PbBr6 and CsPb2Br5 phases in addition to CsPbBr3, a finding consistent with calculations of formation enthalpies by means of the density functional theory showing that these values are very similar for the three ternary phases. We find that these phases can exhibit different spatial distributions inside the film and discuss the influence of the deposition method and synthesis parameters on the resulting phase composition of the Cs amp; 8722;Pb amp; 8722;Br layers

Highly (001)-textured tungsten diselenide WSe2 thin films are crystallized from X-ray amorphous WSex films with Pd-promotion in an H2Se atmosphere. During the crystallization process, the liquid promoter PdSex is driven to the grain boundaries due to the lateral growth of WSe2 platelets and their coalescence. The photoactivity of the WSe2 films is limited by the PdSex crystallites at the grain boundaries of WSe2 platelets. The presence of the PdSex crystallites leads to a metal like behavior of the conductivity versus temperature, whereas their etching leads to a semiconducting behavior of the WSe2 film. After selective etching of these crystallites, the more active WSe2 sites (edges, cavities) are exposed, enhancing the electron transfer to the electrolyte. A photocurrent density of 2 mA cm−2 at 0.35 V vs. reversible hydrogen electrode (RHE) is observed in sulfuric acid (0.5 M H2SO4) using Fe2+/Fe3+ as redox pair under 1 sun (Air Mass (AM) 1.5, 100 mW cm−2) illumination.

This paper reports on the electrical quality of liquid phase crystallized silicon (LPC-Si) on glass for thin-film solar cell applications. Spatially resolved methods such as light beam induced current (LBIC), microwave photoconductance decay (MWPCD) mapping, and electron backscatter diffraction were used to access the overall material quality, intra-grain quality, surface passivation, and grain boundary (GB) properties. LBIC line scans across GBs were fitted with a model to characterize the recombination behavior of GBs. According to MWPCD measurement, intra-grain bulk carrier lifetimes were estimated to be larger than 4.5 µs for n-type LPC-Si with a doping concentration in the order of 10$^{16}$ cm$^{−3}$. Low-angle GBs were found to be strongly recombination active and identified as highly defect-rich regions which spatially extend over a range of 40–60 µm and show a diffusion length of 0.4 µm. Based on absorber quality characterization, the influence of intra-grain quality, heterojunction interface, and GBs/dislocations on the cell performance were separately clarified based on two-dimensional (2-D)-device simulation and a diode model. High back surface recombination velocities of several 10$^5$ cm/s are needed to get the best match between simulated and measured open circuit voltage (V$_{o c}$), indicating back surface passivation problem. The results showed that V$_{o c}$ losses are not only because of poor back surface passivation but also because of crystal defects such as GBs and dislocation.

Erratum

The limited long-term stability of metal halide perovskite-based solar cells is a bottleneck in their drive toward widespread commercial adaptation. The organic hole-transport materials (HTMs) have been implicated in the degradation, and metal oxide layers are proposed as alternatives. One of the most prominent metal oxide HTM in organic photovoltaics is MoO

The limited long-term stability of metal halide perovskite-based solar cells is a bottleneck in their drive toward widespread commercial adaptation. The organic hole-transport materials (HTMs) have been implicated in the degradation, and metal oxide layers are proposed as alternatives. One of the most prominent metal oxide HTM in organic photovoltaics is MoO3. However, the use of MoO3 as HTM in metal halide perovskite-based devices causes a severe solar cell deterioration. Thus, the formation of the MoO3/CH3NH3PbI3-xClx (MAPbI3-xClx) heterojunction is systematically studied by synchrotron-based hard X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. Upon MoO3 deposition, significant chemical interaction is induced at the MoO3/MAPbI3-xClx interface: substoichiometric molybdenum oxide is present, and the perovskite decomposes in the proximity of the interface, leading to accumulation of PbI2 on the MoO3 cover layer. Furthermore, we find evidence for the formation of new compounds such as PbMoO4, PbN2O2, and PbO as a result of the MAPbI3-xClx decomposition and suggest chemical reaction pathways to describe the underlying mechanism. These findings suggest that the (direct) MoO3/MAPbI3-xClx interface may be inherently unstable. It provides an explanation for the low power conversion efficiencies of metal halide perovskite solar cells that use MoO3 as a hole-transport material and in which there is a direct contact between MoO3 and perovskite.

Recent advancements in perovskite solar cell performance were achieved by stabilizing the α-phase of FAPbI3 in nip-type architectures. However, these advancements could not be directly translated to pin-type devices. Here, we fabricated a high-quality double cation perovskite (MA0.07FA0.93PbI3) with low bandgap energy (1.54 eV) using a two-step approach on a standard polymer (PTAA). The perovskite films exhibit large grains (∼1 μm), high external photoluminescence quantum yields of 20%, and outstanding Shockley-Read-Hall carrier lifetimes of 18.2 μs without further passivation. The exceptional optoelectronic quality of the neat material was translated into efficient pin-type cells (up to 22.5%) with improved stability under illumination. The low-gap cells stand out by their high fill factor (∼83%) due to reduced charge transport losses and short-circuit currents >24 mA cm-2. Using intensity-dependent quasi-Fermi level splitting measurements, we quantify an implied efficiency of 28.4% in the neat material, which can be realized by minimizing interfacial recombination and optical losses.

Photovoltaic devices based on Cu(In,Ga)Se2 (CIGSe) absorbers are among the most attractive non-Si alternatives. The key to their steadily increasing efficiency is a post-deposition treatment (PDT) with alkali salts. For co-evaporated CIGSe, a RbF-PDT was demonstrated as the most efficient, however, the mechanism of the RbF influence on the CIGSe absorber is not completely understood. Here, we focus on the impact of RbF on the surface of co-evaporated CIGSe absorbers in dependence on their bulk composition. Surface-as well as bulk-sensitive methods with overlapping information depths are used to examine an overall depth profile of RbF-free and RbF-treated CIGSe samples with different Cu contents. We show a gradual depletion of copper towards the surface for the as-deposited CIGSe absorber layers. The following RbF-PDT sharpens this effect especially for the sample grown with the overall lower Cu content. Under the Cu-depleted surface layer, the composition of the CIGSe gradually changes until it reaches the respective bulk composition. As a result of the RbF-PDT, Ga diffuses towards the surface and Rb gets incorporated at the surface where GaF3 and RbInSe2 secondary phases are formed, respectively. A higher Cu content leads to less surface oriented Ga diffusion, less Rb incorporation and to a thinner RbInSe2 layer. A thinner RbInSe2 barrier layer, in turn, maintains the gain in open-circuit voltage and prevents the fill factor loss of the CIGSe device.

The presence of in-gap states, especially deep ones, that act as recombination centers in solar-cell absorbers influence the phototransport properties of the films, and thus, strongly affect the performance of the corresponding solar cells. The type and density of such defects is influenced by the deposition process. In particular, for $\mathrm{Cu}({\mathrm{In}}_{1\text{\ensuremath{-}}x}{\mathrm{Ga}}_{x}){\mathrm{Se}}_{2}$, it is well established that the presence of a small amount of alkali metal atoms (e.g., $\mathrm{Na}$) improves the performance of the solar cell. Furthermore, in a coevaporation process, a $\mathrm{Cu}$-rich [[$\mathrm{Cu}$]/([$\mathrm{In}$] + [$\mathrm{Ga}$]) g 1] intermediate step decreases the density of extended structural defects, such as stacking faults. Here, we apply temperature-dependent and intensity-dependent photoconductivity measurements, along with Shockley-Read-Hall model calculations, to study the phototransport properties of $\mathrm{Cu}({\mathrm{In}}_{1\text{\ensuremath{-}}x}{\mathrm{Ga}}_{x}){\mathrm{Se}}_{2}$ films with and without a $\mathrm{Cu}$-rich process step, as well as with and without $\mathrm{Na}$. Our experimental and theoretical results indicate a correlation between the presence of planar defects and the formation of a shallow recombination level. Our results further suggest that $\mathrm{Na}$ eliminates deep recombination centers, and thus, increases the lifetime of the photogenerated charge carriers.

Photoinduced phase separation, which limits the available band gap energies for photovoltaic applications, was reported for a range of mixed-halide perovskites. A microscopic understanding of the phase separation mechanism is still lacking but may be beneficial to rationalize limitations as well as enable the design of phase-stable perovskite semiconductors. In this letter, electron-beam-induced phase separations and transformations were investigated in a small crystallite of CsPb(Br0.8I0.2)3 by means of in situ high-resolution imaging in a transmission electron microscope. The acquired time series was evaluated using principal and independent component analysis to classify the structural change during the illumination by the electron beam. A more iodine-rich phase with the approximate composition of CsPb(Br0.6I0.4)3 was found to form at the edges of the particle, while a ternary pure bromide phase of CsPbBr3 remained at its center. These results provide an atomistic picture of in-grain phase segregation into iodide-rich phases at grain boundaries and bromide-rich phases in the interior of the grain.

Significant structural evolution occurs during the deposition of ${\mathrm{CuInSe}}_{2}$ solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to consume highly defected grains. Cu substitutes for In in the near grain boundary regions, turning them into a Cu-Se phase topotactic with the ${\mathrm{CuInSe}}_{2}$ grain interiors. Together with density functional theory and molecular dynamics calculations, we reveal how this Cu-Se phase makes the grain boundaries highly mobile.

Liquid-phase crystallization (LPC) of thin silicon layers on glass substrates is a technique to fabricate solar cells with low energy and material consumption and open-circuit voltages comparable to multicrystalline silicon wafer cells. We studied the impact of different passivation layers deposited with plasma-enhanced chemical vapor deposition (PECVD) on the cell quality. Silicon nitride (SiNx) and ultrathin silicon oxide (SiO x ) layers with varying thicknesses were used. In addition, we plasma-treated the SiN x surface to form a thin silicon oxynitride (SiO x N y ) passivation layer. Plasma oxidation is an attractive alternative to PECVD, since thicknesses of ultrathin layers can be controlled easier as compared with PECVD. We found that the cell performance is influenced by the passivation layer. Particularly, cells on the 9 nm PECVD SiO x passivation layer are worse than cells on the 11 nm SiO x N y layer. We modeled cell parameters employing ASPIN3 to estimate effective diffusion lengths. Using transmission electron microscopy as well as electron energy loss spectroscopy, we studied the effect of the plasma treatment on the morphology and elemental distribution at the interface between passivation layer and LPC-Si absorber. Our best interdigitated back contacted solar cell with an efficiency >14% is based on the SiO x N y layer.

Cu In,Ga Se2 CIGSe is a promising absorber material for thin film photovoltaic devices. A key procedure to achieve high efficiencies is the application of alkali fluoride postdeposition treatments PDT of the CIGSe surface. While the effects of the PDT on the directly impacted CIGSe front surface have been subject to extensive studies, less is known about the impact on the deeply buried CIGSe Mo interface. Exposing the CIGSe absorber backside by stripping it off the Mo back contact allows to use surface sensitive photoelectron spectroscopy to study the chemical and electronic structure of this interface in unprecedented detail. CIGSe Mo stacks prepared using NaF only and combined NaF RbF with optimal and excess amount of RbF PDT are studied. Rb is detected accumulating at the backside of the RbF treated CIGSe absorbers in conjunction with a depletion of Na. The exposed CIGSe backsides display a Cu deficient surface region, with increased presence of Rb correlating with a decreased Cu content. Rb appears to be incorporated into the Cu deficient absorber region as previously detected on the front surface. However, in contrast to the front surface, no distinct, secondary Rb amp; 63743;In amp; 63743;Se type phase is found at the back surface

A laser-based bottom-up technique for the fabrication of Cu(In,Ga)Se2 (CIGSe) micro solar cells is presented. We use femtosecond laser-induced forward transfer (LIFT) to transport a metallic precursor composed of copper, indium, and gallium onto a molybdenum back contact layer on a glass substrate. A CIGSe absorber forms by subsequent selenization. An array of micro absorbers with defined spacing is fabricated to solar cells and characterized under concentrated light illumination. The solar cell array exhibited a conversion efficiency of 1.4‰ at 1 sun as well as a significant efficiency enhancement of 68% rel. under 20-fold concentration. This work demonstrates the possibility of directly grown micrometer-sized solar cells based on chalcogenide absorber layers, enabling effective material usage.

The selenization of metallic Cu-Zn-Sn-Ge precursors is a promising route for the fabrication of low-cost and efficient kesterite thin film solar cells. Nowadays, efficiencies of kesterite solar cells are still below 13 %. For Cu(In,Ga)Se2 solar cells, the formation of compositional gradients along the depth of the absorber layer has been demonstrated to be a key requirement for producing thin film solar cells with conversion efficiencies above the 22 % level. No clear understanding has been reached so far about how to produce these gradients in an efficient manner for kesterite compounds, but among the possible candidates, Ge arises as one of the most promising ones. In the present work, we evaluate the potential of incorporating Ge in Cu2ZnSnSe4 to produce compositional gradients in kesterites. Synchrotron-based in-situ energy-dispersive X-ray diffraction and X-ray fluorescence has been used to study the selenization of Cu-Zn-Sn-Ge metallic precursors. We propose a reaction mechanism for the incorporation of Ge atoms into the kesterite lattice after the formation of Cu2ZnSnSe4. Electron microscopy reveals that the annealing process leads to Cu2Zn(Sn,Ge)Se4 absorber layers with an increase of Ge content towards the back contact with independence of the original location of Ge in the precursor layer. The effect of the Ge gradient on the optoelectronic properties of the absorber layer has been evaluated with room temperature cathodoluminescence. The implications of the results for the development of kesterite solar cells are discussed, with the aim of encouraging new synthesis routes for compositionally graded absorbers.

In the present work, a brief overview is given on how to apply transmission TEM as well as scanning electron microscopy SEM and their related techniques electron diffraction, energy dispersive X ray spectrometry, electron energy loss spectroscopy, electron holography; electron backscatter diffraction, electron beam induced current, cathodoluminescence for the analysis of interfaces between individual layers or extended structural defects in a thin amp; 64257;lm stack. All examples given in the present work were recorded on Cu In, Ga Se2 thin amp; 64257;lm solar cells, however, the shown experimental approaches may be used on any similar thin amp; 64257;lm semiconductor device. A particular aspect is the application of various techniques on the same identical specimen area, in order to enhance the insight into structural, com positional, and electrical properties. For aberration corrected TEM, the spatial resolutions of such measurements can be as low as on the subnanometer scale. However, when dealing with semiconductor devices, it is often necessary to characterize electrical and optoelectronic properties at larger scales, of few 10 nm up to even mm, for which SEM is more appropriate. At the same time, these larger scales provide also enhanced statistics of the analysis. In the present review, it is also outlined how to apply SEM techniques in combination with scanning probe and optical microscopy, on the same identical positions. Altogether, a multiscale toolbox is provided for the thorough analysis of structure property relationships in thin amp; 64257;lm solar cells using correlative microscopy approaches

The present contribution is a summary of an event that was organized as a special evening session in Symposium V Chalcogenide Thin Film Solar Cells at the E MRS 2016 Spring Meeting, Lille, France. The presentations in this session were given by the coauthors of this paper. These authors present retrospectives of key developments in the amp; 64257;eld of Cu In,Ga S,Se 2 solar cells as they themselves had witnessed in their laboratories or companies. Also, anecdotes are brought up, which captured interesting circumstances in that evolutionary phase of the amp; 64257;eld. Be cause the focus was on historical perspectives rather than a comprehensive review of the amp; 64257;eld, recent develop ments intentionally were not addressed

We study the Cu(In,Ga)Se2 absorber fabrication by fast atmospheric pressure selenization of metal precursor films utilizing elemental selenium vapor from independent sources. We find that a high Se supply during selenization leads to the generally observed Ga accumulation at the back contact, while a reduced Se supply leads to a more homogeneous Ga distribution within the absorber. By optimizing the precursor as well as the Ga in‐depth distribution in the CIGSe layer, a conversion efficiency of 15.5% was achieved.

The use of water amp; 8208;in amp; 8208;salt electrolyte WISE i. amp; 8201;e., a highly concentrated aqueous solution in rechargeable batteries has received increasing attention due to the significantly expanded electrochemical window compared to the limited voltage of conventional aqueous electrolytes. It enables the use of more positive negative electrode material couples in aqueous batteries, resulting in an enhanced output voltage. However, one of the challenges is to identify promising anode materials for the water amp; 8208;in amp; 8208;salt Li amp; 8208;ion batteries WIS amp; 8208;LIBs . Herein we for the first time demonstrate that MoS3, an amorphous chain amp; 8208;like structured transitional metal trichalcogenide, is promising as anode in the WIS amp; 8208;LIBs. In this work, hollow MoS3 nanospheres were synthesized via a scalable room amp; 8208;temperature acid precipitation method. When applied in WIS amp; 8208;LIBs, the prepared MoS3 achieved a high specific capacity of 127 amp; 8197;mAh g at the current density of 0.1 amp; 8197;A g and good stability over 1000 cycles. During operation, MoS3 underwent irreversible conversion to Li2MoO4 with H2S and H2 evolution during the initial Li ion uptake, and was then converted gradually to a more stable and reversible LixMoOy 2 amp; 8804;y amp; 8804;4 phase along cycling. Amorphous Li amp; 8208;deficient Lix amp; 8208;mMoOy MoOz was formed upon delithiation. Nevertheless, MoS3 outperformed MoO3 in WIS amp; 8208;LIBs, which could be accredited to its initial one amp; 8208;dimensional molecular structure and the amorphous nature of the delithiated product facilitating charge transport. These results demonstrated a novel routine for synthesizing metal sulfides with hollow structures using a template amp; 8208;based method and push forward the development of metal sulfides for aqueous energy storage applications

Thin-film solar cells based on polycrystalline absorbers have reached very high conversion efficiencies of up to 23-25%. In order to elucidate the limiting factors that need to be overcome for even higher efficiency levels, it is essential to investigate microscopic origins of loss mechanisms in these devices. In the present work, a high efficiency (21% without anti-reflection coating) copper indium gallium diselenide (CIGSe) solar cell is characterized by means of a correlative microscopy approach and corroborated by means of photoluminescence spectroscopy. The values obtained by the experimental characterization are used as input parameters for two-dimensional device simulations, for which a real microstructure was used. It can be shown that electrostatic potential and lifetime fluctuations exhibit no substantial impact on the device performance. In contrast, nonradiative recombination at random grain boundaries can be identified as a significant loss mechanism for CIGSe solar cells, even for devices at a very high performance level., Achieving higher efficiencies for thin-film solar cells always requires identification of the limiting factors. Here Krause et al. show that inhomogeneously distributed net doping or lifetime have little impact while recombination at grain boundaries is one of the main loss mechanisms for high performance Cu(In,Ga)Se2 solar cells.

Significant structural evolution occurs during the deposition of CuInSe2 solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to consume highly defected grains. Cu substitutes for In in the near grain boundary regions, turning them into a Cu-Se phase topotactic with the CuInSe2 grain interiors. Together with density functional theory and molecular dynamics calculations, we reveal how this Cu-Se phase makes the grain boundaries highly mobile.

Cuprous oxide (Cu2O) is a promising material for solar-driven water splitting to produce hydrogen. However, the relatively small accessible photovoltage limits the development of efficient Cu2O based photocathodes. Here, femtosecond time-resolved two-photon photoemission spectroscopy has been used to probe the electronic structure and dynamics of photoexcited charge carriers at the Cu2O surface as well as the interface between Cu2O and a platinum (Pt) adlayer. By referencing ultrafast energy-resolved surface sensitive spectroscopy to bulk data we identify the full bulk to surface transport dynamics for excited electrons rapidly localized within an intrinsic deep continuous defect band ranging from the whole crystal volume to the surface. No evidence of bulk electrons reaching the surface at the conduction band level is found resulting into a substantial loss of their energy through ultrafast trapping. Our results uncover main factors limiting the energy conversion processes in Cu2O and provide guidance for future material development.

International audience

High-efficiency Cu(In,Ga)Se2 (CIGS) thin-film solar cells are based on polycrystalline CIGS absorber layers, which contain grain boundaries, stacking faults, and dislocations. While planar defects in CIGS layers have been investigated extensively, little is still known about the impact of dislocations on optoelectronic properties of CIGS absorbers. Herein, evidence for an optoelectronic inactivity of dislocations in these thin films is given, in contrast to the situation at grain boundaries. This unique behavior is explained by the extensive elemental redistribution detected around dislocation cores, which is connected with the dislocation strain field, probably leading to a shift of defect states toward the band edges.

Interface recombination at the absorber buffer interface impedes the efficiency of a solar cell with an otherwise excellent absorber. The internal voltage or the quasi-Fermi level splitting (qFLs) measures the quality of the absorber. Interface recombination reduces the open circuit voltage (VOC) with respect to the qFLs. The present work explores a facile sulfur-based post-deposition treatment (S-PDT) to passivate the interface of CuInS2 thin films grown under Cu-rich conditions, which show excellent qFLs values, but much lower VOCs. The CuInS2 absorbers are treated in three different S-containing solutions at 80 oC. Absolute calibrated photoluminescence and current-voltage measurements demonstrate a reduction of the deficit between qFLs and VOC in the best S-PDT device by almost one third compared to the untreated device. Analysis of temperature dependence of the open-circuit voltage shows increased activation energy for the dominant recombination path, indicating less interface recombination. In addition, capacitance transient measurements reveal the presence of slow metastable defects in the untreated solar cell. The slow response is considerably reduced by the S-PDT, suggesting passivation of these slow metastable defects. The results demonstrate the effectiveness of solution based S-treatment in passivating defects, presenting a promising strategy to explore and reduce defect states near the interface of chalcogenide semiconductors.

Cu2SnS3 is investigated as a potential solar absorber material, which is known to exist in several polymorphs. In the present work, the transition to the most efficient monoclinic polymorph is investigated and an explanation is given why this one seems to be the best for solar cells. Cubic, mixed polymorphs and monoclinic polymorphs are synthesised with increasing temperature. Photoluminescence spectra of the mixed and cubic polymorphs show mainly defect emissions below the band-gap energy, while the monoclinic modification shows only one sharp peak, which is attributed to the conduction to valence band transition. The monoclinic polymorph also grows in combination with a secondary phase containing sodium, NaxCuSnS3, with x between 0.5 and 1. It exhibits a cubic (F43m) crystal structure like CuSn3.75S8 and a band-gap of around 1.6 eV. Devices with absorber layers of monoclinic Cu2SnS3, in which NaxCuSnS3 is either present or removed, gave similar power conversion efficiencies of above 1%.