No abstract

With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation.

Graphites, as well as other intercalation materials used in lithium-ion batteries, change their color upon electrochemical insertion of lithium ions. In this study, in situ colorimetry was developed as a straightforward technical method to measure the local state of charge of lithium-ion battery electrodes. A laboratory cell with a glass window was built for in situ characterization of intercalation materials. Calibration curves of red, green, and blue color values vs state of charge were acquired and used for mapping of lithium distribution in battery electrodes. The lithium distribution in anodes of aged lithium-ion batteries was found to be highly heterogeneous.

Partially amorphous La 0.6 Sr 0.4 CoO 3-δ (LSC) thin-fi lm cathodes are fabricated using pulsed laser deposition and are integrated in free-standing micro-solid oxide fuel cells (micro-SOFC) with a 3YSZ electrolyte and a Pt anode. A low degree of crystallinity of the LSC layers is achieved by taking advantage of the miniaturization of the cells, which permits low-temperature operation (300-450 °C). Thermomechanically stable micro-SOFC are obtained with strongly buckled electrolyte membranes. The nanoporous columnar microstructure of the LSC layers provides a large surface area for oxygen incorporation and is also believed to reduce the amount of stress at the cathode/ electrolyte interface. With a high rate of failure-free micro-SOFC membranes, it is possible to avoid gas cross-over and open-circuit voltages of 1.06 V are attained. First power densities as high as 200-262 mW cm −2 at 400-450 °C are achieved. The area-specifi c resistance of the oxygen reduction reaction is lower than 0.3 Ω cm 2 at 400 °C around the peak power density. These outstanding fi ndings demonstrate that partially amorphous oxides are promising electrode candidates for the next-generation of solid oxide fuel cells working at low-temperatures.

Indium tin oxide (ITO) is commonly used as the transparent bottom electrode for organic solar cells. However, it is known that the cost of the ITO is quite high due to the indium element, and in some studies ITO coated glass substrate is found to be the most expensive component of device fabrication. Moreover, indium migration from ITO can cause stability issues in organic solar cells. Nevertheless, the use of ITO as the bottom electrode is still dominating in the field. Here, we explore the possibility of using fluorine doped tin oxide (FTO) as an alternative to ITO for the bottom electrode of organic solar cells particularly on semi-transparent cells. We present side-by-side comparisons on their optical, morphological and device properties and suggest that FTO could be more suitable than ITO as the bottom electrode for glass substrate based organic photovoltaic devices.

Free‐standing electrolyte membranes for low‐temperature micro‐solid oxide fuel cells (micro‐SOFCs) are prepared by aerosol‐assisted chemical vapor deposition (AA‐CVD), a cost‐effective, non‐vacuum thin‐film deposition technique. Thin, yttria‐stabilized zirconia (YSZ) membranes (50–400 nm) as well as bilayer membranes of YSZ and gadolinia‐doped ceria are prepared at temperatures of 600 °C and below. AA‐CVD, which is a gas‐phase deposition method, allows for the synthesis of precursor‐free crystalline layers, thereby limiting the development of tensile stress. High membrane survival rates of around 90% are thus obtained. The columnar structure of the electrolyte ensures high oxygen‐ion conductivity and results in negligible ohmic losses. Using sputtered platinum electrodes, the demonstration of a micro‐SOFC based on AA‐CVD electrolyte is achieved and first power density data of 166 mW cm‐2 at 410 °C is obtained.

Micro-solid oxide fuel cells (micro-SOFC) are predicted to be of high energy density and are potential power sources for portable electronic devices. A micro-SOFC system consists of a fuel cell comprising a positive electrode-electrolyte-negative electrode (i.e. PEN) element, a gas-processing unit, and a thermal system where processing is based on micro-electro-mechanical-systems fabrication techniques. A possible system approach is presented. The critical properties of the thin film materials used in the PEN membrane are discussed, and the unsolved subtasks related to micro-SOFC membrane development are pointed out. Such a micro-SOFC system approach seems feasible and offers a promising alternative to stateof-the-art batteries in portable electronics.

The residual stress and buckling patterns of free‐standing 8 mol.% yttria‐stabilized‐zirconia (8YSZ) membranes prepared by pulsed laser deposition and microfabrication techniques on silicon substrates are investigated by wafer curvature, light microscopy, white light interferometry, and nanoindentation. The 300 nm thin 8YSZ membranes (390 μm × 390 μm) deposited at 25 °C are almost flat after free‐etching, whereas deposition at 700 °C yields strongly buckled membranes with a compressive stress of –1,100 ± 150 MPa and an out‐of‐plane‐displacement of 6.5 μm. These latter membranes are mechanically stable during thermal cycling up to 500 °C. Numerical simulations of the buckling shape using the Rayleigh–Ritz‐method and a Young's modulus of 200 GPa are in good agreement with the experimental data. The simulated buckling patterns are used to extract the local stress distribution within the free‐standing membrane which consists of tensile and compressive stress regions that are below the failure stresses. This is important regarding the application in, e.g., microsolid oxide fuel cell membranes which must be thermomechanically stable during microfabrication and device operation.