Contract type : Fixed-term contract
Level of qualifications required : Graduate degree or equivalent
Fonction : PhD Position
The Inria Sophia Antipolis - Méditerranée center counts 34 research teams as well as 8 support departments. The center's staff (about 500 people including 320 Inria employees) is made up of scientists of different nationalities (250 foreigners of 50 nationalities), engineers, technicians and administrative staff. 1/3 of the staff are civil servants, the others are contractual agents. The majority of the center’s research teams are located in Sophia Antipolis and Nice in the Alpes-Maritimes. Four teams are based in Montpellier and two teams are hosted in Bologna in Italy and Athens. The Center is a founding member of Université Côte d'Azur and partner of the I-site MUSE supported by the University of Montpellier.
This doctoral project will be conducted in the Atlantis project-team, in close collaboration with researchers in physics from the Sunlit team at C2N (Center for Nanoscience and Nanotechnology) in Palaiseau.
Atlantis is a joint project-team between Inria and the Jean-Alexandre Dieudonné Mathematics Laboratory at University Nice Sophia Antipolis. The team gathers applied mathematicians and computational scientists who are collaboratively undertaking research activities aiming at the design, analysis, development and application of innovative numerical methods for systems of partial differential equations (PDEs) modeling nanoscale light-matter interaction problems. In this context, we develop the DIOGENeS software suite [https://diogenes.inria.fr/], which implements several Discontinuous Galerkin (DG) type methods tailored to the systems of time- and frequency-domain Maxwell equations possibly coupled to differential equations modeling the behavior of propagation media at optical frequencies. DIOGENeS is a unique numerical framework leveraging the capabilities of DG techniques for the simulation of multiscale problems relevant to nanophotonics and nanoplasmonics.
The research activities of the Sunlit team [http://sunlit-team.eu] are concerned with different aspects of the development of photovoltaic (PV) solar cell devices, from the study of semiconductor material properties to the design of solar cell structures that exhibit outstanding sunlight absorption and conversion performances. The team conducts both experimental studies (from the nano-imprinting of material layers that constitute a solar cell, to the characterization of solar cell devices) and modeling studies using third-party numerical tools such as the RCWA (modal type method) and the FDTD (finite difference type method).
The ultimate success of photovoltaic (PV) cell technology requires substantial progress in both cost reduction and efficiency improvement. An actively studied approach to simultaneously achieve these two objectives is to leverage light-trapping schemes. Light trapping allows solar cells to absorb sunlight using an active material layer that is much thinner than the material’s intrinsic absorption length. This then reduces the amount of materials used in PV cells, which cuts cell cost in general, and moreover facilitates mass production of PV cells that are based on less abundant materials. In addition, light trapping can improve cell efficiency, since thinner cells provide better collection of photo-generated charge carriers. Enhancing the light absorption in ultrathin film silicon solar cells is thus of paramount importance for improving efficiency and reducing cost.
The theory of light trapping was initially developed for conventional solar cells where the light-absorbing film is typically many wavelengths thick. From a ray optics perspective, conventional light trapping exploits the effect of total internal reflection between the semiconductor material (such as silicon) and the surrounding medium (usually assumed to be air). By roughening the semiconductor-air interface, one randomizes the light propagation directions inside the material. The effect of total internal reflection then results in a much longer propagation distance inside the material and hence a substantial absorption enhancement. For such light trapping schemes, the standard theory, first developed by E. Yablonovitch, shows that the absorption enhancement factor has an upper limit of 4n2/sin2 θ, where θ is the angle of the emission cone in the medium surrounding the cell. This limit is referred to as the Yablonovitch limit or the 4n2 limit, since one is primarily concerned with structures with θ = π/2 which has a near-isotropic emission cone. For nanophotonic films with thicknesses comparable or even smaller than wavelength scale, the ray optics picture and some of the basic assumptions in the conventional theory are no longer applicable. In that case, it can be shown that the absorption enhancement factor can go far beyond the 4n2 limit with proper design. In this context, there is significant recent interest in designing ultrathin crystalline silicon solar cells with active layer thickness of a few micrometers . Efficient light absorption in such thin films requires both broadband antireflection coatings and effective light trapping techniques, which often have different design considerations.
The general objective of this Ph.D. project is to develop several numerical strategies for the design of ultrathin solar cells with improved light trapping properties. The focus will be on the optimization (or inverse design) of the nanostructuring of the material layers (metallic and semiconductor layers) that constitute the solar cell device. In order to do so, one will combine the use of a high order DGTD solver  from the DIOGENeS software suite for the optical characterization of a solar cell device, with statistical learning-based global optimization strategies  namely, CMA-ES (Covariance Matrix Adaptation Evolution Strategy) and metamodeling-based EGO (Efficient Global Optimization) methods, which are offered by the DiceOptim library [http://dice.emse.fr/]. This research will address several specific topics related to (1) the time-domain numerical modeling of light absorption in semiconductor materials used in the PV field, (2) the development of efficient optimization strategies for wideband propagation problems exhibiting multiple resonances and, (3) exploring advanced light trapping schemes yielding novel nanostructuring patterns. In the context of this joint Ph.D. project, the candidate will be mainly localized at Inria with several visits at C2N. Moreover, this Ph.D. project will also be conducted in collaboration with research engineers at Total Gas, Renewables & Power and Total R&D Computational Science and Engineering.
 H.L. Chen, A. Cattoni, R. De Lépinau, A.W. Walker, O. Höhn, D. Lackner, G. Siefer, M. Faustini, N. Vandamme, J. Goffard, B. Behaghel, C. Dupuis, N. Bardou, F. Dimroth and S. Collin, A 19.9%-efficient ultrathin solar cell based on a 205-nm-thick GaAs absorber and a silver nanostructured back mirror, Nat. Energy, Vol. 4, pp. 761-767, 2019.
 S. Lanteri, C. Scheid and J. Viquerat, Analysis of a generalized dispersive model coupled to a DGTD method with application to nanophotonics, SIAM J. Sci. Comp., Vol. 39, No. 3, pp. 831-859, 2017.
 R. Duvigneau and P. Chandrashekar, Kriging-based optimization applied to flow control, Int. J. Num. Meth. Fluids, Vol. 69, pp. 1701–1714, 2011.
Master in computational science and engineering, scientific computing or electrical engineering.
Required knowledge and skills are a sound knowledge of finite element type methods for solving PDEs and numerical optimization techniques; a concrete experience in numerical modeling for computational electromagnetics; strong software development skills, preferably in Fortran 95/2008.
Previous research experience in applied nanophotonics will clearly be an asset for this position.
Duration: 36 months
Location: Sophia Antipolis, France
Gross Salary per month: 1982€brut per month (year 1 & 2) and 2085€ brut/month (year 3)
Inria is the French national research institute dedicated to digital science and technology. It employs 2,600 people. Its 200 agile project teams, generally run jointly with academic partners, include more than 3,500 scientists and engineers working to meet the challenges of digital technology, often at the interface with other disciplines. The Institute also employs numerous talents in over forty different professions. 900 research support staff contribute to the preparation and development of scientific and entrepreneurial projects that have a worldwide impact.
Defence Security :
This position is likely to be situated in a restricted area (ZRR), as defined in Decree No. 2011-1425 relating to the protection of national scientific and technical potential (PPST).Authorisation to enter an area is granted by the director of the unit, following a favourable Ministerial decision, as defined in the decree of 3 July 2012 relating to the PPST. An unfavourable Ministerial decision in respect of a position situated in a ZRR would result in the cancellation of the appointment.
Recruitment Policy :
As part of its diversity policy, all Inria positions are accessible to people with disabilities.
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|Titel||2020-02344 - PhD Position F/M Numerical optimization of ultrathin solar cells|
|Job location||2004 route des Lucioles, BP 93 06902 Sophia Antipolis|
|Gepubliceerd||juli 22, 2020|
|Sluitingsdatum||september 30, 2020|
|Vakgebieden||Electromagnetisme,   Optica,   Berekeningstheorie,   Toegepaste wiskunde,   Getaltheorie,   Computationele fysica,   Elektrotechniek,   Computationele wiskunde,   Computationale techniek,    and 1 more. Fotonica  |