Paul Beutel’s research while affiliated with Protestant University of Applied Sciences Freiburg and other places

III-V compound semiconductors provide a high degree of flexibility in bandgap engineering and can be realized through epitaxial growth in high quality. This enables versatile spectral matching of photovoltaic absorber materials as well as the fabrication of complex layer structures of vertically stacked subcells and tunnel junctions. This work presents progress in two fields of applications of III-V photovoltaics: concentrator solar cells and photonic power converters. We present latest results in advancing solar energy conversion efficiencies to 47.6% based on a wafer-bonded four-junction concentrator solar cell. Furthermore, we provide an overview of the latest development results regarding photonic power converters, showcasing several record devices. We briefly introduce a new metallization technique using electro-plated silver for handling high currents and first 10-junction InGaAs devices for optical telecommunication wavelengths. Overall, this paper highlights the potential of III-V compound semiconductors in achieving high efficiencies and spectral matching, offering promising prospects for future applications.

Mandatory compliance with the most stringent exhaust emission limits is to be expected in the future, e.g. the new European exhaust emission limits for commercial vehicle diesel engines. The new, stringent NOx EURO VII commercial vehicle limits in particular, which are expected not before 2025, can only be achieved with very efficient heating technology for new, adapted exhaust aftertreatment systems. The highly dynamic Real Drive Emission (RDE) test cycles containing a high amount of cold starts that will be used in this context will confront the Euro VII commercial vehicle emission reduction systems with some challenges that are quite difficult to overcome. After the publication of the first promising results of component and initial engine test bench trials with the new heating measure for exhaust aftertreatment (EAT), a.k.a. the CatVap® system (see also previous publications, such as at the 15th MTZ/ATZ On-/Off- Highway Conference or MTZ 01/2021 et al.), more highly dynamic component and commercial vehicle engine test bench trials were carried out with an OEM medium duty and a heavy duty engine, each in conjunction with up-to-date combined exhaust gas aftertreatment systems of the EURO VI+ (e,f) generation, in conjunction with the newly established development consortium consisting of Fraunhofer ISE, Albonair GmbH, Vitesco Technologies Emitec GmbH and Thomas Magnete GmbH. This article shows the most relevant dynamic tests that were carried out (their basis being real world drive cycles, e.g. the special urban cycle), graphically visualized as well as in the form of corresponding test interpretations. Many of these tests were performed using dynamic test cycles, and their results are presented accordingly, including raw emission data in a percentage comparison with the effect on the tailpipe end emissions. It could be demonstrated that low NOx-levels can be achieved with a Euro VI+ EAT box and CatVap®. These tests have also shown strong fuel benefits with significantly lower NOx-emissions through CatVap® in comparison to internal heating measures. CatVap® can mitigate the trade-off between low NOx-emissions and low fuel consumption.Keywords:CatVapFast heatingHeat retentionExhaust Aftertreatment SystemReal Driving EmissionsEnabler Near Zero-Emission IC Engines

Multijunction solar cells (MJSCs) have attracted attention as next-generation solar cells. In particular, GaAs//Si-based MJSCs are highly efficient with low cost and are expected to gain new applications, such as on-vehicle integrations. In this article, we examined a highly efficient In _0.49 Ga _0.51 P/Al _0.06 Ga _0.94 As//Si three-junction solar cell. The bottom Si cell has a tunnel oxide passivated contact structure. The key technology used to fabricate this solar cell is a stacking method that uses Pd nanoparticles (Pd-NPs) and metal-assisted chemical etching (MacEtch) for the bonding interface, which is improved from our previous “smart stack” technology. The MacEtch method has a feature of selective etching for Si around a metal body. Pd-NPs selectively invade the Si cell through the surface of the Si oxide layer, thereby improving the bonding resistivity between the GaAs-based cell and Si cell. Further, this technology aids the management of the bonding gap width by controlling the Pd-NP invasion depth. As a result, an efficiency of 27.6% for the aperture area was attained. The proposed technology is useful for the connection of Si-based cells, enhancing the development of GaAs//Si-based tandem solar cells.

Multijunction (MJ) solar cells achieve high efficiencies by effectively utilizing the solar spectrum. Previously, we have developed III‐V MJ solar cells using smart stack technology, a mechanical stacking technology that uses a Pd nanoparticle array. In this study, we fabricated an InGaP/AlGaAs//CuxIn1−yGaySe2 three‐junction solar cell by applying modified smart stack technology with a Pd nanoparticle array and adhesive material. Using adhesive material (silicone adhesive), the bonding stability was improved conspicuously. The total efficiency achieved was 27.2% under AM 1.5 G solar spectrum illumination, which is a better performance compared to our previous result (24.2%) for a two‐terminal solar cell. The performance was achieved by optimizing the structure of the upper GaAs‐based cell and by using a CuxIn1−yGaySe2 solar cell with a specialized performance for an MJ configuration. In addition, we assessed the reliability of the InGaP/AlGaAs//CuxIn1−yGaySe2 three‐junction solar cell through a heat cycle test (from −40°C to +85°C; 50 cycles) and were able to confirm that our solar cells show high resistivity under severe conditions. The results demonstrate the potential of III‐V//CuxIn1−yGaySe2 MJ solar cells as next‐generation photovoltaic cells for applications such as vehicle‐integrated photovoltaics; they also demonstrate the effectiveness of modified smart stack technology in fabricating MJ cells.

Today’s challenge is to almost comply with the emission limits 100% in Real Drive Emission (RDE) behavior, especially in the cold season, the so-called “cold city rides”, which are characterized by the fact that during the stop and go rides in the city at no time a sufficient temperature for an efficient exhaust aftertreatment is reached. The future Euro6+ or certainly the expected new Euro7 limit values will therefore only be achieved with suitable effective thermal heating, heat retention as well as regeneration measures for the exhaust aftertreatment (EAT) system. CatVap® is an easily scalable system for both diesel and gasoline engines that provides highly efficient thermal energy, simply from fuel (diesel, gasoline, synthetic fuels), coupled into the exhaust system and thus provides the thermal energy required for exhaust gas conversion. It is fast, highly dynamically controllable, can be used as a catalytic burner for rapid heating during a cold start of the engine system. Furthermore, CatVap® can then be used as a light-off accelerator (by fuel tailoring to synthesis gas (syngas) and shorter alkenes) for the Diesel Oxidation Catalyst (DOC) and the Selective Catalytic Reduction (SCR) catalyst. CatVap can also be used for the diesel particulate filter, for its effective active regeneration or temperature control for continuous regeneration. The CatVap system is an important key enabler for near zero-emission internal combustion (IC) engines that can be demonstrated in the near future.

The terrestrial photovoltaic market is dominated by single–junction silicon solar cell technology. However there is a fundamental efficiency limit at 29.4%. This is overcome by multi‐junction devices. Recently, a GaInP/GaAs//Si wafer bonded triple‐junction two–terminal device was presented with a 33.3% (AM1.5g) efficiency. Here it is analyzed how this device is improved to reach a conversion efficiency of 34.1%. By improving the current matching an efficiency of 35% (2 terminals, AM1.5g) is expected. This article is protected by copyright. All rights reserved.