Influence of Periodic Surface Nanopatterning Profiles on Series Resistance in Thin-Film Crystalline Silicon Heterojunction Solar Cells

In the frame of the development of thin crystalline silicon solar cell technologies, surface nanopatterning of silicon is gaining importance. Its impact on the material quality is, however, not yet fully controlled.We investigate here the influence of surface nanotexturing on the series resistance of a contacting scheme relevant for thin-film crystalline silicon heterojunction solar cells. Two dimensional periodic nanotextures are fabricated using a combination of nanoimprint lithography and either dry or wet etching, while random pyramid texturing is used for benchmarking. We compare these texturing techniques in terms of their effect on the series resistance of a solar cell through a study of the sheet resistance (Rsh ) and contact resistance (Rc) of its front layers, i.e., a sputtered transparent conductive oxide and evaporated metal contacts. We have found by four-point probe and the transfer length methods that dry-etched nanopatterns render the highest Rsh and Rc values. Wet-etched nanopatterns, on the other hand, have less impact on Rc and render Rsh similar to that obtained from the nontextured case.Comment: Authors' post-print version in Abdo et al., IEEE Journal of Photovoltaics, July 201

Porous multi-junction thin-film silicon solar cells for scalable solar water splitting

© 2018 Elsevier B.V. Monolithic solar water splitting devices implemented in an integrated design approach, i.e. submerged in the electrolyte, pose a significant limitation when it comes to up-scaling. The ion transport distances around the monolith are long and consequently, the ionic Ohmic losses become high. This fact turns out to be a bottleneck for reaching high device efficiency and maintaining optimum performance upon up-scaling. In this paper, we propose a new device design for integrated monolithic solar water splitting based on porous multi-junction silicon solar cells. Simulation results highlight that porous monoliths can benefit from lower ionic Ohmic losses compared to dense monoliths for various pore geometries and monolith thicknesses. In particular, we show how micrometer scale pore dimensions could greatly reduce Ohmic losses, thereby minimizing overpotentials. A square array of holes with a diameter of 20 µm and a period of 100 µm was fabricated on single-junction and multi-junction amorphous and microcrystalline silicon solar cells. A small impact on the open circuit voltage (Voc) and short circuit current density (Jsc) was obtained, with porous triple junction solar cells reaching Voc values up to 1.98 V. A novel device design is proposed based on porous triple-junction silicon-based solar cells.status: publishe

Influence of the pattern shape on the photonic efficiency of front-side periodically patterned ultrathin crystalline silicon solar cells

Patterning the front side of an ultra-thin crystalline silicon (c Si) solar cell helps keeping the energy conversion efficiency high by compensating for the light absorption losses. A super-Gaussian mathematical expression was used in order to encompass a large variety of nanopattern shapes and to study their influence on the photonic performance. We prove that the enhancement in the maximum achievable photo-current is due to both impedance matching condition at short wavelengths and to the wave nature of light at longer wavelengths. We show that the optimal mathematical shape and parameters of the pattern depend on the c Si thickness. An optimal shape comes with a broad optimal parameter zone where fabricating errors would have much less influence on the efficiency. We prove that cylinders are not the best suited shape. To compare our model with a real slab, we fabricated a nanopatterned c Si slab via Nano Imprint Lithography.Comment: 21 pages, 7 figure