A5071261337- Perovskite Materials and Applications
- Chalcogenide Semiconductor Thin Films
- Ferroelectric and Piezoelectric Materials
- Quantum Dots Synthesis And Properties
- Acoustic Wave Resonator Technologies
- Mechanical and Optical Resonators
- Force Microscopy Techniques and Applications
- Advanced MEMS and NEMS Technologies
- Physics of Superconductivity and Magnetism
- Solid-state spectroscopy and crystallography
- Advanced Sensor and Energy Harvesting Materials
- Quantum and electron transport phenomena
- Conducting polymers and applications
- Photorefractive and Nonlinear Optics
- Semiconductor materials and interfaces
- Silicon and Solar Cell Technologies
- Optical measurement and interference techniques
- Advanced Electrical Measurement Techniques
- Advanced Thermoelectric Materials and Devices
- Advanced Adaptive Filtering Techniques
- Adhesion, Friction, and Surface Interactions
- Mechanical and Thermal Properties Analysis
- Magnetic properties of thin films
- Material Properties and Applications
- Thermal properties of materials
École Polytechnique Fédérale de Lausanne
2018-2023
Swiss Center for Electronics and Microtechnology (Switzerland)
2022
Infineon Technologies (Germany)
2021
Thinfilm (Sweden)
2019
Forschungszentrum Jülich
1993-2007
Siemens (Germany)
1995
Silicon solar cells are approaching their theoretical efficiency limit of 29%. This limitation can be exceeded with advanced device architectures, where two or more stacked to improve the harvesting energy. In this work, we devise a tandem perovskite layer conformally coated on silicon bottom cell featuring micrometric pyramids—the industry standard—to its photocurrent. Using an additive in processing sequence, regulate crystallization process and alleviate recombination losses occurring at...
We reveal an iodine vapor-induced degradation mechanism in formamidinium–lead-iodide-based perovskite solar cells stressed under combined heat and light illumination.
Cesium–formamidinium-based mixed-halide perovskite materials with optical band gaps ranging from 1.5 to 1.8 eV are investigated by variable-angle spectroscopic ellipsometry. The determined complex refractive indices shown depend on the fabrication procedure and environmental conditions during processing. This data is complemented additional structural characterization, as well demonstration of efficient solar cells. Finally, used in simulations provide guidelines for optimization...
The mechanisms controlling the degradation of p–i–n perovskite solar cells in reverse bias are identified using various optoelectronic and microstructural characterization techniques.
Abstract The current climate and energy crisis urgently needs solar cells with efficiencies above the 29% single junction efficiency bottleneck. Silicon/perovskite tandem are a solution, which is attracting much attention. While silicon/perovskite in 2‐terminal 4‐terminal configurations well documented, three‐terminal concept still its infancy. It has significant advantages under low light intensities as opposed to concentrated sunlight, critical factor designing for low‐cost terrestrial...
This work investigates halide segregation in methylammonium-free wide bandgap perovskites by photoluminescence quantum yield (PLQY) and advanced electron microscopy techniques. Our study reveals how the formation of nano-emitting low-energy domains embedded a matrix, located at surfaces grain boundaries, enables PLQY up to 25%. Intensity-dependent measurement PL excitation spectroscopy revealed efficient charge funnelling failure optical reciprocity between absorption emission, limiting use...
We report on the influence of a surface layer prevailing perovskites piezoelectricity measured by piezoresponse force microscopy. Surface sensitive measurements show that this consists chemisorbates and physisorbates. The can be removed to large extent heating sample under ultrahigh vacuum conditions. It is shown effect treatment material significant as potential difference applied no longer reduced voltage drop across adsorbate layer. As consequence internal electric field higher in...
Regular patterns of ferroelectric PbTiO3 nanostructures (see Figure) with lateral dimensions down to 30–60 nm have been grown onto platinized Si substrates by chemical solution deposition. The high registration the grains is achieved “top–down”-generated templates TiO2 dots as seeds for their Ferroelectricity was verified piezoresponse force microscopy.
The in-plane image of piezoresponse force microscopy (PFM) generally exhibits a higher resolution and less noise than the out-of-plane image. Geometrical considerations indicate that optical amplification is ≈40 times larger amplification. We experimentally confirm this explanation in dedicated setup.
Using BaTiO3 as a piezoelectric model system we compare finite element with experimental data to demonstrate the impact of grain topography on in-plane response at perimeter. Our findings emphasize need for careful consideration both electric field and tensor orientation. An analysis is given showing that piezoresponse function two directions field, whereas out-of-plane all three applied field. The effect an adsorbate layer quantified typical material parameters.
The correlation between rate of light-induced phase segregation and deep defect formation observed in mixed-halide perovskites. importance grain size determining the terminal was highlighted.
Piezoresponse force microscopy (PFM) provides valuable insight into the inverse lateral and vertical piezoelectric effects on nanoscale. Ideally, these contributions are separated detections of a deflected laser beam quadrupole diode. In contrast to known crosstalk by rotated diode that causes identical signals in both channels, we report due geometrical constraints cantilever is inherent PFM. For BaTiO3 (001) nanograin show response attributable 1∕8th response. From this value deduce actual...
We report on the integration of fully functional ferroelectric PbTiO3 nanostructures typically less than 100nm lateral extension into a low-k dielectric hydrogen silsesquioxane film. Chemical mechanical polishing layer down to an overall thickness below nanoparticles height exposes structures. After confirmation piezoelectricity individual embedded grains, gold electrode pads are deposited characterize several these grains in parallel. Evidence switching is observed and discussed within...
We report on the influence of system-immanent asymmetries interpretation in-plane piezoresponse force microscopy (PFM). As PFM is a surface scanning method, electromechanical interaction probe tip and sample key aspect all experiments. An initial characterization topography, state, conductivity mandatory to separate their signal from response due an polarization state. Our findings underline that any reduction radial symmetry in tip-sample system creates otherwise symmetry-prohibited signal.
Abstract We report on the reduction of piezoresponse in KNbO 3 originating from a surface layer. An analysis with sensitive measurements shows that this layer consists chemisorbates and physisorbates. Heating sample under ultra high vacuum conditions removes perovskite to large extend. This treatment has drastic effect as potential difference applied is no longer reduced by voltage drop across adsorbate layer, leading higher electric field compared case an Experiments simulations are...
Scanning thermal microscopy (SThM) enables conductivity (λ) measurements with a lateral resolution down to few tens of nanometers. The present work investigates ways improve SThM images recorded resistive probes. Probes based on resistance thermometry act both as thermometer and Joule heated nanoscale heat source. influence amplitude frequency the applied heating voltage image quality was systematically studied. To connect investigated parameters temperature change at apex probe,...
Tandem solar cells that feature a high-bandgap perovskite cell on top of lower bandgap silicon have the potential to reach efficiencies >30%. Here, we present versatile hybrid deposition method yields conformal directly textured bottom cells, prerequisite achieve highest photocurrents and hence efficiencies. Furthermore, this low-temperature evaporation/spin-coating 2-step produces high-quality materials with different bandgaps, here varied in range 1.5 eV 1.8 eV. This flexibility enables...
We demonstrate a double barrier long Josephson tunnel junction device of overlap geometry with an external electric contact to the middle electrode. The junctions were fabricated standard Nb/Al-AlO/sub x//Nb process. To exhibit fluxon coupling effects in stacked junctions, intermediate Nb layer thickness between two barriers has be order London penetration depth, i.e. 90 nm for sputtered films. By using planarization process, we able avoid steep steps on wafer and so reduce nm....
Highly textured Nb-films were grown by electron-beam evaporation on sapphire substrates. The crystalline quality was examined Rutherford-backscattering-channeling and X-ray diffraction methods. channeling minimum yield is 2%. On c-plane the evaluation of rocking curve measurements yielded 99.98% [111] Nb // (0001) 0.02% [110] sapphire. Measurements microbridges with widths ranging from 2 mu m to 100 (film thickness 500 nm) showed a residual resistivity ratio (R/sub 295K//R/sub 10K/) up 90...