Projects

The aim of the project 'PARASOL' is to integrate stable and efficient metal oxide passivation protection layers with multi-absorber photoelectrochemical (PEC) cells consisting of a combination of III-V semiconductors and Si by adapted energetic coupling. The III-V photoabsorbers are prepared by metal-organic chemical vapor deposition. The metal oxide protective layers are deposited by atomic layer deposition. Both methods are industrially scalable. The III-V semiconductor surface is precisely tuned by a combination of optical in situ spectroscopy and photoelectron spectroscopy (PES) to achieve a defect-free heterointerface. The surface preparation of the III-V semiconductor is modified and its influence on the nucleation of the metal oxide protective layer and the electronic tailoring of the heterointerface is investigated. Specific modifications of the sequence of the metal and oxygen precursors are introduced. The deposition of the first monolayers of the metal oxide layer is investigated in detail and the heterointerface is determined with PES. The passivation layers are analyzed with regard to composition, crystallinity and morphology.

The joint team from Yale University and Ilmenau University of Technology is researching the use of efficient semiconducting photoabsorbers for organic synthesis. Semiconductors are known to efficiently convert light into charge, and photocatalysts control the charge transfer processes to drive redox reactions to form stable products. Photocatalytic organic synthesis is similar to photoredox catalysis for the coevolution of reductive and oxidative reactions in situ, but produces surface-bound organic molecules during coevolution. However, the relationship between the energetics and kinetics of charge transfer and surface reactivity is less understood, limiting the design of synthetic pathways using photocatalysts. To address this gap, the team investigated a model reaction of photocatalytic para-xylene oxidation to produce terephthalic acid driven by TiO2-coated planar aluminum-gallium-indium-phosphide semiconductors. Theoretical calculations will correspond to the measured energetics and product selectivity and elucidate the reaction pathways at the surface. The joint research priorities include i.) the correlation between surface chemistry and hole transfer energetics, ii.) co-evolution to achieve product selectivity, and iii.) implementation of the vapor phase reactor. This cross-disciplinary investigation should involve future workers in the US and Germany. Simple reactor implementation fills the gap in public education for chemical The simple reactor implementation fills the gap in public education for chemical production and also enriches interdisciplinary education curricula in this newly initiated international outreach project.

The joint project "Development of future solar cell technologies and materials for space applications (SMART)" addresses the key technologies for the production of next-generation space solar cells, which can be used to meet the requirements of future satellite platforms in terms of increased performance, cost efficiency and application diversity. The planned technology and material development will focus in particular on metamorphic semiconductor materials for multi-junction solar cells with high radiation hardness as well as the processes for the realization of ultra-light solar cells and solar cell assemblies. The project consortium consists of AZUR SPACE Solar Power GmbH (project management), the academic partners TU Ilmenau and Philipps University Marburg as well as Fraunhofer ISE.

TU Ilmenau

The aim of the overall project is the development of demonstrators with an area of 1300 cm^2 for direct solar hydrogen production with an efficiency > 15 %. The focus of the subproject of TU lmenau in H2Demo is on the improvement of III-V-on-Si heteroepitaxy and the development and application of analytical methods. Specifically, the preparation and detection of III-V nucleation layers on Si(001) with significantly reduced defect density will be performed at TU Ilmenau and the effect of different defects arising at the interface on the electronic properties of the layers will be investigated. The developed processes will be transferred to Fraunhofer ISE. During the start-up of the high-throughput process in the 2nd phase, the TU Ilmenau will play a supporting role through process development and analysis. In analytics, the TU Ilmenau provides measurement technology in the field of charge carrier lifetime measurement and develops novel in situ and operando measurement technology for the analysis of surface properties and charge carrier dynamics as well as performance characteristics in the environment of the photoelectrochemical cell.

TU Ilmenau

The aim of the DEPECOR project is to combine highly efficient multi-absorber structures in a systemic approach, with structures that have already been established in photovoltaics, where their critical interfaces and photovoltages will be adapted for CO₂ reduction, with specific corrosion protection layers and efficient catalysts specifically selected according to their material and shape. For the non-assisted, direct, sunlight-induced CO₂ reduction, the photoelectrochemical (PEC) cells must generate a photovoltage of approximately 3 V. This is possible with multiple absorber structures based on III-V semiconductors. These PEC cells consist of several stacked semiconductor structures (sub-cells) that absorb the light in different spectral ranges. Thus, an effective exploitation of the sunlight spectrum is achieved and the energy losses are significantly reduced compared to single absorber systems. The total voltage is composed of the sum of the voltages of each sub-cell and therefore sufficient to drive the chemical reactions directly.

The TU Ilmenau (TU-IL) group will develop and test integrated III-V semiconductor, photoelectrocatalytic half-cells. In order to increase the stability of the cells and enhance the performance, metal oxide protective layers will be deposited by atomic layer deposition (ALD) at the TU Munich (TUM) and the heterointerfaces will be examined in cooperation with TU-IL. Highly active catalysts will be developed at the Helmholtz-Zentrum Berlin (HZB) and integrated into the cell structure. The interaction of the photocathode with the electrolyte and the quantitative development of the reaction products will be measured at the TUM, HZB, TU-IL and at the Joint Center of Artificial Photosynthesis (USA). The project partner AZUR SPACE Solar Power GmbH (AZUR) will deliver suitable industrially scalable multi-absorber structures on germanium and III-V substrates, while the Fraunhofer Institute for Solar Energy Systems (ISE) will develop the layer structures on silicon substrates. The associated partner École Polytechnique Fédérale de Lausanne (EPFL) will investigate the activity of specific Cu catalysts and will support the modeling of the prototype of CO2 reduction systems for non-assisted fuel production. The project partner AZUR as well as the associated partners BASF and Evonik will advise the prototype development regarding the technology transfer in order to develop the planned commercial product.

III-V multi-junction solar cells achieve by far the highest conversion efficiencies of up to 38% from sunlight to electricity. The use of III-V semiconductors in photovoltaic flat modules has so far appeared to be highly complex and therefore difficult due to high manufacturing and substrate costs, but the partners at Fraunhofer ISE, TU Ilmenau and the University of Marburg have recently been able to show that III-V compounds of high quality can also be directly deposited on silicon. Only a few over 30 % can be realized on Si.

The combination of established silicon solar technology with the advantages of III-V semiconductors opens new options for highly efficient solar cells and is the focus of the MehrSi project. By reducing defect densities and using optimized solar cell structures, GaInP/GaAs(P) multi-junction solar cells grown directly on Si with > 30 % efficiency are to be demonstrated for the first time.

Heteroepitaxial III-V semiconductor layer systems on silicon substrates promise high application potential both in the development of highly efficient multiple solar cells and in the integration of optoelectronic devices in silicon-based circuits. However, a breakthrough in the widespread implementation of such technologies has so far failed due to an excessive concentration of lattice defects in the heteroepitaxial III-V layers. In this project, different complementary microscopy techniques will be used to improve the crystalline quality of GaP films deposited on single-crystalline silicon substrates using industry-relevant metal-organic vapor-phase epitaxy by quantifying and characterizing such crystal defects and developing avoidance strategies such as substrate conditioning. The focus of the work is on the application of very surface-sensitive low-energy electron microscopy, with which it is possible through different contrast mechanisms to detect such defects in large sample areas on a microscopic length scale without further pretreatment of the samples, as well as to image dynamic processes with sufficient speed. In addition, sub-steps of substrate conditioning and layer preparation simulated in the microscope will be investigated, in particular with regard to the initial layer growth.

In the OptiSolar project, the researchers aim to increase the efficiency of thin-film solar cells with a-Si heteroemitters, to optimize the properties of a-SiNx antireflective layers and the interface to c-Si, as well as interface problems between glass substrate and intermediate layers in laser-crystallized silicon. At the end of their research the potential degradation mechanisms could be understood and avoided as well as the efficiency could be improved and thus costs could be reduced.