2020-02344 - PhD Position F/M Numerical optimization of ultrathin solar cells
Le descriptif de l’offre ci-dessous est en Anglais

Type de contrat : CDD

Niveau de diplôme exigé : Bac + 5 ou équivalent

Fonction : Doctorant

A propos du centre ou de la direction fonctionnelle

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.

Contexte et atouts du poste

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 behaviour  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).

Mission confiée

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 [1]. Efficient  light absorption in such  thin films requires both broadband  antireflection coatings  and effective  light trapping techniques,   which  often   have  different   design  considerations.

Principales activités

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  [2]  from the DIOGENeS software suite for the optical characterization of a solar cell device, with statistical learning-based global optimization strategies [3] 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.

[1] 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.

[2] 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.

[3] 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.


  • Subsidized meals
  • Partial reimbursement of public transport costs
  • Leave: 7 weeks of annual leave + 10 extra days off due to RTT (statutory reduction in working hours) + possibility of exceptional leave (sick children, moving home, etc.)
  • Possibility of teleworking (after 6 months of employment) and flexible organization of working hours
  • Professional equipment available (videoconferencing, loan of computer equipment, etc.)
  • Social, cultural and sports events and activities
  • Access to vocational training
  • Social security coverage


Duration: 36 months
Location: Sophia Antipolis, France
Gross Salary per month: 1982€brut per month (year 1 & 2) and 2085€ brut/month (year 3)