IPVF Postdoc: Multi-functional bonding for two-terminal III-V/Si tandem solar cells with 30% efficiency


Function: Postdoc

Contract type: COD

Starting date: ASAP

Working place: Palaiseau, Paris area

Duration: 36 months

Education: PhD in Materials science, physics of semiconductor or related field.

Salary: profile dependent.

IPVF in brief

Become an actor of the Energy Transition by joining a team driven by innovation and impact to address today’s most decisive challenges.

IPVF – Institut Photovoltaïque d’Île-de-France, is a global Research, Innovation and Education center, which mission is to accelerate energy transition through science & technology.

Gathering industrial PV leaders (EDF, Total, Air Liquide, Horiba and Riber) and world-renowned academic research teams (CNRS, Ecole Polytechnique), multi-disciplinary and international IPVF teams conduct research for clean energy technologies. Supported by the French State, IPVF is labelled Institute for Energy Transition (ITE).

IPVF at a glance:

  • An ambitious Scientific and Technological Program: from tandem solar cell technologies to economy & market assessment, state-of-the art characterization, photocatalysis and concepts breakthrough.
  • A state-of-the-art technological platform: more than 100 tools, located in cleanrooms (advanced characterization, materials deposition, prototypes for fabrication, modelling…).
  • A high-standard Education program (M.S. and PhD students).

Job context

IPVF and C2N are seeking a postdoctoral researcher to work on new 2-terminals III-V on Si tandem architecture based on an original and scalable wafer bonding method integrating light trapping. The project will be carried out in close collaboration with the Laboratoire Chimie de la Matiere Condensée de Paris at the Sorbonne University / College de France (Dr. M. Faustini) and the Fraunhofer Institute for Solar Energy Systems (ISE).

‍More information about the research program and IPVF here:

IPVF Research Program involving this postdoc position: https://www.ipvf.fr/fr/stephane-collin-introducing-ipvf-programme-3-low-cost-tandem-iii-v-cell-on-silicon/

Website: https://www.ipvf.fr

Main missions

The candidate will directly report to the Programs Deputy Director of IPVF and will integrate a dynamic and talented team driven by innovation and results.

Her/his main missions will consist in:

1) Wafer bonding – IPVF, C2N, EDF and Sorbonne University developed and patented a scalable wafer bonding method for the fabrication of a 2-terminals III-V on Si tandem solar cell. The method avoids the use of dedicated wafer bonder equipments, expensive wafer cleaning and it can actually accomodate a certain wafer rougness (for example it is compatible with TOPCon technology). At present the method makes use of hybrid organic-inorganic bonding layer. The aim of this task will be to test the long-term stability of tandem solar cells fabricated with such wafer bonding method and – if necessary – to modify the bonding process/materials to avoid the use of any organic components for improved stability. Some of these strategies are already detailed in mentioned patent and need to be experimentally validated.

2) Sol-gel derived materials development – The patented wafer bonding architecture filled by IPVF, C2N, EDF and Sorbonne University make use of a multi-layer stack of materials sandwitched in between the top and the bottom cells.  These layers are transparent, conductive and with an opportune refractive index to ensure: the photon recycling for the top-cell, the transmission of red photons destined to the Si bottom cell and – when nanostructured – efficient light trapping to increase the short-circuit current for the two solar cells. Absorption and tension losses in this multi-layer stack are already extremely limited (< 0.5 mA/cm2 and < 20 mV) but they could be further reduced. There is also a margin to further increase the positive photon recycling effect. The aim of this task is to develop new sol-gel derived materials to address these issues and to make them compatible with the bonding process. Moreover, these materials will be compatible with the Nanoimprint process used to fabricate the light-trapping structures and/or compatible with a nanostructured front surface (i.e. inverted pyramids) of the Si solar cell.

3) Light trapping integration – C2N and Fraunhofer recently demonstrated a ultrathin (200 nm) GaAs solar cell with record efficiency of 20% using efficient light trapping that compensates the minor absorption due to the reduced absorber thickness. C2N and IPVF shown by electromagnetic simulations that a similar approach can be applied to a 2-terminals III-V on Si tandem: it will allow reducing III-V top cell thickness of a factor 5 without short-circuit losses. Moreover, C2N and IPVF proposed and patented a III-V on Si tandem design to obtain photon recycling in the III-V top cell thus increasing the Tandem Voc and efficiency (up to 1% absolute). The aim of this task is to integrate light-trapping strategy to: i) reduce the III-V solar cell thickness and exploit photon recycling to increase the Voc and efficiency of the Tandem on Si.



  • Materials science,
  • Physics of semiconductors,
  • Thin films.


  • Hands-on experience in a fablab,
  • Knowledge of nanophotonics,
  • Demonstrated experience in nanofabrication and sol-gel chemistry is an asset,
  • Previous experience in photovoltaics device fabrication and characterization is a plus.

Self-management skills

  • Curious, entreprising and creative,
  • Autonomous,
  • Good communication skills.


Cover letter and résumé to be sent to: andrea.cattoni@c2n.upsaclay.fr, stephane.collin@c2n.upsaclay.fr and rh@ipvf.fr

Need a direct line?

Feel free to contact us for more information about our offers.

  • +33(0)1 69 86 58 60
  • contact@ipvf.fr
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