Duplicated-Junction Solar Cells: An Innovative Approach for Energy Harvesting at Ultra-High Concentrations
New architecture of solar cells called duplicated junction cells.
The concept constitutes an innovative alternative to conventional III-V multi-junction cells and consists in duplicating each sub-cell in several p-n junctions of the same material.
The architecture makes it possible to considerably reduce resistive losses and therefore to operate efficiently at very high concentration factors (> 1000 suns).
Silicon and germanium are semiconductors of interest for energy applications. Electrochemical etching allows to nanostructurated semiconductors with nanoscale size and tunable morphology.
Chemical vapor infiltration with acetylene and controled steps as well as temperature control conduct to graphene deposition into the mesoporous structure (all the surface is covered). Then advanced material characterizations using Raman, SEM, TEM, XPS for understanding the structure and nature of the deposition are performed.
Finally, thermoelectric properties are studied on this new kind of nanomaterial.
Author : Stephanie Sauze
Nanostructured Si pillars as a compliant substrate for defect-free heteroepitaxy
A perfectly compliant substrate would allow the monolithic integration of high-quality semiconductor materials such as Ge and III-V on Silicon (Si) substrate, enabling novel functionalities on the well-established low-cost Si technology platform.
Here, we demonstrate a compliant Si substrate allowing defect-free epitaxial growth of lattice mismatched materials. The method is based on the deep patterning of the Si substrate to form micrometer-scale pillars and subsequent electrochemical porosification.
The investigation of the epitaxial Ge crystalline quality by X-ray diffraction, transmission electron microscopy and etch-pits counting demonstrates the full elastic relaxation of defect-free microcrystals. The achievement of dislocation free heteroepitaxy relies
on the interplay between elastic deformation of the porous micropillars, set under stress by the lattice mismatch between Ge and Si, and on the diffusion of Ge into the mesoporous patterned substrate attenuating the mismatch strain at the Ge/Si interface.
Defects in Ge/Si substrate for integration of III-V materials
Electrochemical etching of a virtual Ge/Si dislocated substrate through the dislocations.
Thermal annealing induces coalescence of porous material to form voids
The voids allow dislocations to be deflected or annihilated to prevent them from reaching the surface
Reduction of threading dislocations density up to 104/cm2
A promising approach for integration of III-V materials for high efficiency solar cells.
Y. A. Bioud et al., ‘Uprooting defects to enable high-performance III–V optoelectronic devices on silicon’, Nat. Commun., vol. 10, no. 1, p. 4322, Dec. 2019, doi: 10.1038/s41467-019-12353-9.
The use of high performance anodic materials such as silicon or germanium is made difficult by the physical and chemical degradations undergone by them once put in batteries, i.e. the volumic expansion and the formation of solid electrolyte interface (SEI).
Nanostructuring these materials makes it possible to increase their life cycle and their mechanical behaviour.
In addition, the carbon functionalization has been demonstrated to be effective in reducing the formation of SEI and so the irreversible capacity.
Based on these knowledges, we developped nanocomposites based on mesoporous germanium and graphene, using mature and scalable processes, the electrochemical etching and chemical vapor deposition.
Theses nanocomposites have demonstrated superior electrochemical performance, in high energy density as well as high power density applications.
Highlights
Integration of mesoporous semiconductor as on-chip anode.
Semiconductor nanostructuration and graphene-like coating for enhanced life cycle.
First demonstration of these anodes for high-energy and high-power density regimes.
The method paves the way to inexpensive mass production of microbatteries and solid-state batteries.
