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An essential step toward enabling the production of renewable and cost-efficient fuels is an improved understanding of the performance of energy conversion materials. In recent years, there has been growing interest in ternary metal oxides. Particularly, α-SnWO4exhibited promising properties for application to photoelectrochemical (PEC) water splitting. However, the number of corresponding studies remains limited, and a deeper understanding of the physical and chemical processes in α-SnWO4is necessary. To date, charge-carrier generation, separation, and transfer have not been exhaustively studied for SnWO4-based photoelectrodes. All of these processes depend on the phase composition, not only α-SnWO4but also on the related phases SnW3O9and WO3, as well as on their spatial distributions resulting from the coating synthesis. In the present work, these processes in different phases of tin tungstate films were investigated by transient surface photovoltage (TSPV) spectroscopy to complement the analysis of the applicability of α-SnWO4thin films for practical PEC oxygen evolution. Pure α-SnWO4films exhibit higher photoactivities than those of films containing secondary SnW3O9and WO3phases due to the higher recombination of charge carriers when these phases are present.

We investigated triple-halide perovskite (THP) absorber layers with 5 mol % MAPbCl3added to the double-halide perovskite (Cs0.22FA0.78)Pb(I0.85Br0.15)3. As a deposition method, a highly scalable printing technique, slot-die coating, with a subsequent annealing step was used. We found a strong power conversion efficiency (PCE) dependence of the corresponding solar cells on the annealing temperature. The device performance deteriorated when increasing the annealing temperature from 125 to 170 °C, mainly via losses in the open-circuit voltage (Voc) and in the fill factor (FF). To understand the mechanisms behind this performance loss, extensive characterizations were performed on both, the THP thin films and the completed solar-cell stacks, as a function of annealing temperature. Correlative scanning electron microscopy analyses, i.e., electron backscatter diffraction, energy-dispersive X-ray spectroscopy, and cathodoluminescence, in addition to X-ray diffraction and photoluminescence, confirmed the presence of PbI2platelets on the surface of the THP thin films. Moreover, the area fraction of the PbI2platelets on the film surface increased with increasing annealing temperature. The deteriorated device performance when the annealing temperature is increased from 125 to 170 °C is explained by the increased series resistance and increased interface recombination caused by the PbI2platelets, leading to decreased Vocand FF values of the solar-cell devices. Thus, the correlative analyses provided insight into microscopic origins of the efficiency losses.

The phase mixture CsPb2Br5/CsPbBr3has raised interest as a promising material system for light emission, light detection, and even for photovoltaic devices owing to its high luminescence yield and improved device performance when compared with pure CsPbBr3devices. Given that CsPb2Br5and CsPbBr3exhibit similar formation enthalpies, thermal treatment can induce phase transformations between them. The influence of that transformation on the optoelectronic properties is still unclear. In the present work, we report the effect of elevated-temperature (>580 K) postdeposition annealing on the luminescence of a mixed-phase CsPb2Br5/CsPbBr3thin film deposited by coevaporation. Using combined photoluminescence spectroscopy, X-ray diffraction, and scanning electron microscopy techniques, we found that deep defects at the CsPb2Br5/CsPbBr3interface contribute to quench the CsPbBr3green luminescence and that annealing increases the defect concentration in CsPb2Br5, leading to a strong decrease of the external photoluminescence quantum yield. Our results do not confirm any passivating effect of CsPb2Br5—as-deposited or induced by annealing—as reported by other authors.

In recent years, inorganic cesium–lead–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–Pb–Br thin films, deposited by solution-based 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–Pb–Br films contain ternary Cs4PbBr6and CsPb2Br5phases 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–Pb–Br layers.

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 1016 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 105 cm/s are needed to get the best match between simulated and measured open circuit voltage (Voc), indicating back surface passivation problem. The results showed that Voc losses are not only because of poor back surface passivation but also because of crystal defects such as GBs and dislocation.

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 (SiOx) layers with varying thicknesses were used. In addition, we plasma-treated the SiNx surface to form a thin silicon oxynitride (SiOxNy) 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 SiOx passivation layer are worse than cells on the 11 nm SiOxNy 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 SiOxNy layer.

A direct self-assembly of high-quality, uncoated ZnS nanodots on a given substrate was obtained using two techniques: the sequential and cyclic spray ion layer gas reaction (spray-ILGAR) as well as the simultaneous and continuous spray chemical vapor deposition (spray-CVD). The spray-ILGAR nanodots are homogeneous in size (3–6 nm), regular in shape, and uniform in composition, while the spray-CVD nanodots are larger and irregular in shape with inclusions of ZnO. By employing these two spray-based techniques, the synthesis of nanodots directly assembled on the substrate surface can be realized in a controlled manner, covering a certain range of compositions, tunable sizes, and controllable interparticle distances. In situmass spectrometry was implemented in the real-time process in order to achieve better understanding of the intrinsic chemistry involved. We systematically study the influence of the process parameters on the formation of the nanodots and compare the morphology, composition, and property of the obtained nanodots. Based on these investigations, the underlying mechanism that controls the special growth of the nanodots in spray-ILGAR and spray-CVD processes is proposed. It can account for the similarities and differences of these two kinds of nanodots. A passivation/point contact bilayer, composed of the spray-based ZnS nanodots covered by a homogeneous ILGAR In2S3layer, is used as the buffer in the chalcopyrite solar cells, resulting in the cell performance improvement compared to the pure ILGAR In2S3buffer.

Cu(In,Ga)Se$_2$ (CIGSe) absorber layers used in thin-film solar cells exhibit, when grown in a multistage process, compositional gradients of Ga and In. In this study, the correlations between the Ga gradient and the microstructure are studied by means of transmission electron microscopy (TEM) imaging combined with energy-dispersive X-ray spectroscopy (EDX), allowing the determination of structural defects and elemental distributions at identical sample positions. The occurrence of linear defects (dislocations) and planar defects (stacking faults and microtwins) of CIGSe layers was studied by means of TEM images. The Ga distributions obtained from EDX elemental distribution maps and structural parameters from the literature were used to calculate the lattice parameters c and a and the gradient dc/ dx perpendicular to the substrate. We found a correlation between the magnitude of dc/dx and the occurrence of dislocations within individual large grains. From the presented results, a threshold value of the Ga gradient of 12–13at.%/μm can be estimated for the formation of misfit dislocations.

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 MoO3as 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 MoO3deposition, significant chemical interaction is induced at the MoO3/MAPbI3–xClxinterface: substoichiometric molybdenum oxide is present, and the perovskite decomposes in the proximity of the interface, leading to accumulation of PbI2on the MoO3cover layer. Furthermore, we find evidence for the formation of new compounds such as PbMoO4, PbN2O2, and PbO as a result of the MAPbI3–xClxdecomposition and suggest chemical reaction pathways to describe the underlying mechanism. These findings suggest that the (direct) MoO3/MAPbI3–xClxinterface may be inherently unstable. It provides an explanation for the low power conversion efficiencies of metal halide perovskite solar cells that use MoO3as a hole-transport material and in which there is a direct contact between MoO3and perovskite.

Silicon nitride (SiNx) and silicon oxide (SiOx) grown with plasma‐enhanced chemical vapor deposition are used to passivate the front‐side of liquid‐phase crystallized silicon (LPC‐Si). The dielectric layer/LPC‐Si interface is smooth and layers are well‐defined as demonstrated with transmission electron microscopy. Using electron energy loss spectroscopy a thin silicon oxynitride is detected which is related to oxidation of the SiNxprior to the silicon deposition. The interface defect state density (Dit) and the effective fixed charge density (QIL,eff) are obtained from high‐frequency capacitance‐voltage measurements on developed metal‐insulator‐semiconductor structures based on SiOx/SiNx/LPC‐Si and SiOx/SiNx/SiOx/LPC‐Si sequences. Charge transfer across the SiNx/LPC‐Si interface is observed which does not occur with the thin SiOxbetween SiNxand LPC‐Si. The SiOx/SiNx/LPC‐Si interface is characterized by QIL,eff > 1012cm−2and Dit,MG>1012eV−1 cm−2. With SiOx/SiNx/SiOxstack, both parameters are around one order of magnitude lower. Based on obtained QIL,effand Dit(E) and capture cross sections for electrons and holes of σn= 10−14cm s−1and σp= 10−16cm s−1, respectively, a front‐side surface recombination velocity in the range of 10 cm s−1at both interfaces is determined using the extended Shockley‐Read‐Hall recombination model. Results indicate that field‐effect passivation is strong, especially with SiOx/SiNxstack. Liquid‐phase crystallized silicon is passivated using silicon nitride or a silicon nitride/silicon oxide stack prepared with plasma‐enhanced chemical vapor deposition. The origin of the passivation quality is examined through the determination of the defect state density and the fixed charge density with capacitance‐voltage measurements on developed metal‐insulator‐semiconductor structures. The surface recombination velocity is calculated using the Shockley‐Read‐Hall formalism.