Antonin Faes

Realization of GaInP/Si Dual-Junction Solar Cells With 29.8% 1-Sun Efficiency

Combining a Si solar cell with a high-bandgap top cell reduces the thermalization losses in the short wavelength and enables theoretical 1-sun efficiencies far over 30%. We have investigated the fabrication and optimization of Si-based tandem solar cells with 1.8-eV rear-heterojunction GaInP top cells. The III–V and Si heterojunction subcells were fabricated separately and joined by mechanical stacking using electrically insulating optically transparent interlayers. Our GaInP/Si dual-junction solar cells have achieved a certified cumulative 1-sun efficiency of 29.8% ± 0.6% (AM1.5g) in four-terminal operation conditions, which exceeds the record 1-sun efficiencies achieved with both III–V and Si single-junction solar cells. The effect of luminescent coupling between the subcells has been investigated, and optical losses in the solar cell structure have been addressed.

Silicon Heterojunction Solar Cells With Copper-Plated Grid Electrodes: Status and Comparison With Silver Thick-Film Techniques

Copper electroplating is investigated and compared with common silver printing techniques for the front metallization of silicon heterojunction solar cells. We achieve smaller feature sizes by electroplating, significantly reducing optical shadowing losses and improving cell efficiency by 0.4% absolute. A detailed investigation of series resistance contributions reveals that, at maximum power point, a significant part of the lateral charge-carrier transport occurs inside the crystalline bulk, rather than exclusively in the front transparent conductive oxide. This impacts optimization for the front-grid design. Using advanced electron microscopy, we study the inner structure of copper-plated fingers and their interfaces. Finally, a cell efficiency of 22.4% is demonstrated with copper-plated front metallization.

High-performance hetero-junction crystalline silicon photovoltaic technology

Silicon heterojunction solar cell technology (HJT) takes advantage of ultra-thin amorphous silicon layers deposited on both sides of monocrystalline silicon wafers, enabling excellent silicon wafer surface passivation resulting in high device power output and in addition to efficient use of thin wafers. A full cell processing platform was developed in our laboratory, enabling to achieve > 22 % cell efficiency. Advanced concepts for metallization and interconnection are under study, from fine-line printing combined with SmartWire interconnection to Copper plating. Importantly, we show that the HJT technology intrinsically enables high bifaciality of the cells (> 95 %), and further demonstrates a low thermal coefficient (<; 0.2 - 0.3 %/°C). The high performance of heterojunction cells and SmartWire interconnection based modules allow for very low cost of electricity for Heterojunction based solar systems, with a potential below 6 Euro cents per kWh in Europe, bringing photovoltaics as a very competitive electricity source. It further provides upgrade potential towards 24 % cell efficiency.

Metal-free crystalline silicon solar cells in module

Solar cells interconnection with multiple wires enables the module integration of metal-free silicon heterojunction (SHJ) solar cells. The electrical contact occurs between the transparent conductive oxide (TCO) of the SHJ cell and the low melting point alloy coated on the wires. First proof-of-concept bifacial modules are presented. The module efficiency drop between standard SHJ silver screen-printed cells and metal-free SHJ cell is only 0.5% abs. This drop is related to the high contact resistance at the non-yet optimized TCO/wire interface, higher than typical TCO/silver finger contact resistance.

Solar-hydrogen generation and solar concentration (Conference Presentation)

We successfully demonstrated and reported the highest solar-to-hydrogen efficiency with crystalline silicon cells and Earth-abundant electrocatalysts under unconcentrated solar radiation. The combination of hetero-junction silicon cells and a 3D printed Platinum/Iridium-Oxide electrolyzer has been proven to work continuously for more than 24 hours in neutral environment, with a stable 13.5% solar-to-fuel efficiency. Since the hydrogen economy is expected to expand to a global scale, we demonstrated the same efficiency with an Earth-abundant electrolyzer based on Nickel in a basic medium. In both cases, electrolyzer and photovoltaic cells have been specifically sized for their characteristic curves to intersect at a stable operating point. This is foreseen to guarantee constant operation over the device lifetime without performance degradation. The next step is to lower the production cost of hydrogen by making use of medium range solar concentration. It permits to limit the photoabsorbing area, shown to be the cost-driver component. We have recently modeled a self-tracking solar concentrator, able to capture sunlight within the acceptance angle range +/-45°, implementing 3 custom lenses. The design allows a fully static device, avoiding the external tracker that was necessary in a previously demonstrated +/-16° angular range concentrator. We will show two self-tracking methods. The first one relies on thermal expansion whereas the second method relies on microfluidics.

Silicon heterojunction solar cells with plated contacts for low to medium concentration photovoltaics

Silicon heterojunction (SHJ) technology enables high performance photovoltaics at acceptable cost. In this article, we show that this technology is also well suited for low to medium concentration applications. For this purpose, SHJ cells have been optimized and tested at different illumination levels and temperatures. An interesting increase of the efficiency temperature coefficient is observed with increasing illumination level. This behavior translates in improved performances of the tested SHJ devices under low to medium concentration applications, when operated at temperature above 25°C. This is linked to the behavior of the FF, exhibiting an improvement with increasing temperature while the cell is operated under high illumination level. This phenomenon suggests thermally assisted carrier transport through a barrier probably located at the TCO/p+ a-Si:H interface.